Refraction and muscular imbalance

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Title: Refraction and muscular imbalance
Author: Woolf, Daniel
Language: English
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Copyright Status: Not copyrighted in the United States. If you live elsewhere check the laws of your country before downloading this ebook. See comments about copyright issues at end of book.

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[Illustration: =SKI-OPTOMETER MASTER MODEL 215=

Embodying in a Single Instrument, in Convenient Form,
Cylindrical and Spherical Lenses, in Combination
with Appliances for Testing and Correcting
Muscular Imbalance.]

Refraction and
Muscular Imbalance

_As Simplified Through the Use
of the Ski-optometer_

By
DANIEL WOOLF

WOOLF INSTRUMENT CORPORATION
NEW YORK: 516 FIFTH AVENUE

Published by
THEODORE S. HOLBROOK
NEW YORK

CONTENTS

CHAPTER I Page
SKI-OPTOMETER CONSTRUCTION 1
Convex Spherical Lenses 2
Operates and Indicates Automatically 6
Concave Spherical Lenses 7

CHAPTER II
CYLINDRICAL LENSES 10
Obtaining Correct Focus 11
Why Concave Cylinders Are Used Exclusively 14
Transposition of Lenses 14

CHAPTER III
HOW THE SKI-OPTOMETER ASSISTS IN REFRACTION 17
The Use of the Ski-optometer in Skioscopy 17
A Simplified Skioscopic Method 20
Employing Spheres and Cylinders in Skioscopy 22
Use of the Ski-optometer in Subjective Testing 23
A Simplified Subjective Method 24
Procedure for Using Minus Cylinders Exclusively 26
Constant Attention Not Required 29

CHAPTER IV
IMPORTANT POINTS IN CONNECTION WITH THE
USE OF THE SKI-OPTOMETER 30
Elimination of Trial-Frame Discomfort 30
Rigidity of Construction 31
How to Place the Ski-optometer in Position 32
Cleaning the Lenses 33
Accuracy Assured in Every Test 34
Built to Last a Lifetime 35

CHAPTER V
CONDENSED PROCEDURE FOR MAKING SPHERE AND
CYLINDER TEST WITH THE SKI-OPTOMETER 37
Subjective Distance Test 37
Subjective Reading Test 40

CHAPTER VI
MUSCULAR IMBALANCE 41
The Action of Prisms 42
The Phorometer 43
The Maddox Rod 44
Procedure for Making the Muscle Test 45
Binocular and Monocular Test 47

CHAPTER VII
THE BINOCULAR MUSCLE TEST 48
Made with the Maddox Rod and Phorometer 48
Esophoria and Exophoria 50
Making Muscle Test Before and After
Optical Correction 52
When to Consider Correction of Muscular Imbalance 53
Four Methods for Correction of Muscular Imbalance 54
The Rotary Prism 54
Use of the Rotary Prism in Binocular Muscle Tests 56

CHAPTER VIII
THE MONOCULAR DUCTION MUSCLE TEST 58
Made with Both Rotary Prisms 58
Locating the Faulty Muscle 58
Adduction 59
Abduction 61
Superduction 62
Subduction 63
Procedure for Monocular Muscle Testing 64
Diagnosing a Specific Muscle Case 65

CHAPTER IX
FIRST METHOD OF TREATMENT—OPTICAL CORRECTION 70
Esophoria 70
Treatment for Correcting Esophoria in Children 72
How Optical Correction Tends to Decrease 6°
Esophoria in a Child 74

CHAPTER X
SECOND METHOD OF TREATMENT—MUSCULAR EXERCISE 75
Made with Two Rotary Prisms and Red Maddox Rod 75
Exophoria 75
An Assumed Case 78
Effect of Muscular Exercise 80
Home Treatment for Muscular Exercise—Square Prism
Set Used in Conjunction with the Ski-optometer 82

CHAPTER XI
THIRD METHOD OF TREATMENT—PRISM LENSES 84
When and How Employed 84
Prism Reduction Method 85

CHAPTER XII
A CONDENSATION OF PREVIOUS CHAPTERS ON THE PROCEDURE
FOR MUSCLE TESTING WITH THE SKI-OPTOMETER 87
Four Methods of Treating an Imbalance Case
when the Preceding One Fails 90
Prisms 92
Cyclophoria 92

CHAPTER XIII
CYCLOPHORIA 93
Made with Maddox Rods and Rotary Prisms 93

CHAPTER XIV
CYCLODUCTION TEST 99
Made with the Combined Use of the Two Maddox Rods 99
Treatment for Cyclophoria 102

CHAPTER XV
MOVEMENTS OF THE EYEBALLS AND THEIR ANOMALIES 105
Monocular Fixation 105
Binocular Fixation 106
Orthophoria 107
Heterophoria 107
Squint 108
Varieties of Heterophoria and Squint 109

CHAPTER XVI
LAW OF PROJECTION 114
Suppression of Image 115
Monocular Diplopia 115
Table of Diplopia 116
Movement of Each Eye Singly 117
Subsidiary Actions 118
Field of Action of Muscles 120
Direction of the Gaze 120
Primary Position—Field of Fixation 121
Binocular Movements 121
Parallel Movements 122
Lateral Rotators 123
Eye Associates 124
Movements of Convergence 125
Movements of Divergence 125
Vertical Divergence 126
Orthophoria 126
Heterophoria 126
Subdivisions 126

CHAPTER XVII
SYMPTOMS OF HETEROPHORIA 128
Treatment 130
Destrophoria and Laevophoria 132

The demands of the day for maximum efficiency in the refracting world
are largely accountable for the inception, continuous improvement and
ultimate development of the master model Ski-optometer.

The present volume, dealing with the instrument’s distinctive operative
features, has been prepared not only for Ski-optometer users, but also
for those interested in the simplification of refraction and muscular
imbalance.

The author is indebted for invaluable counsel, to

Louis J. Ameno, M.D., New York.
E. LeRoy Ryer, O.D., New York.
Jos. D. Heitger, M.D., Louisville, Ky.
W. B. Needles, N.D., Kansas City, Mo.

INTRODUCTORY

While in a measure the conventional trial-case still serves its
purpose, so much of the refractionist’s time is consumed through the
mechanical process of individually transferring the trial-case spheres
and cylinder lenses, that far too little thought is given to _muscular
imbalance_, notwithstanding its _importance_ in all refraction cases.

Dr. Samuel Theibold, of Johns Hopkins University, in a recent address
before the American Medical Association, stated that the average
refractionist was inclined to devote an excess of time to general
refraction, completely overlooking the important test and correction of
muscular imbalance. If the latter is to be at all considered, general
refraction must be simplified—without impairing its accuracy—a result
that is greatly facilitated through the use of the Ski-optometer.

One must admit that tediously selecting the required trial-case
lens—whether sphere, cylinder or prism—watching the stamped number on
the handle—continual wiping and inserting each individual lens in a
trial-frame is a time-consuming practise. This is readily overcome,
however, through the employment of the Ski-optometer.

In a word, the Ski-optometer is practically an automatic trial-case,
bearing the same relation to the refracting room as the accepted labor
and time-saving devices of the day bear to the commercial world.

The present volume has accordingly been published, not alone in the
interest of those possessing a Ski-optometer, but also for those
interested in attaining _the highest point of efficiency_ in the work
of refraction and muscular imbalance.

[Illustration:

_Ski-optometer Lens Battery (almost actual size) showing how sphere and
cylinder lenses are procured._

_After obtaining FINAL results, your prescription is automatically
registered, ALL READY for you to transcribe._

Fig. 1—The three time-saving moves necessary in the operation of the
Ski-optometer.]

CHAPTER I

SKI-OPTOMETER CONSTRUCTION

A far better understanding of the instrument will be secured if the
refractionist possessing a Ski-optometer will place it before him,
working out each operation and experiment step by step in its proper
routine.

The three moves as outlined in Fig. 1 should first be thoughtfully
studied and the method of obtaining the spheres and cylinders carefully
observed.

[Illustration: Fig. 2—To Obtain Plano.]

1—Set spherical indicator at “000” as illustrated above.
2—Set cylinder indicator to “0”.
3—Set pointer of supplementary disk at “open”.

The instrument should then be set at zero or “plano,” a position
indicated by the appearance of the three “0 0 0” at the spherical
register, in conjunction with one “0” or zero, for the cylinder at its
register, marked “CC Cyl.”

After this move, the supplementary disk’s pointer should be set at
“open” (Fig. 2).

[Illustration: Fig. 3—To obtain sphericals, turn this Single Reel as
shown by dotted finger. This assures an automatic and simultaneous
registration at sphere indicator of focus of lens appearing at sight
opening.]

CONVEX SPHERICAL LENSES

A careful study will show that the Ski-optometer’s spherical lenses
are obtained by merely turning the smaller reel (Fig. 3). The
first _outward_ turn of this reel, toward the temporal side of the
instrument, draws into position in regular order the spherical lenses
+.25, +.50, +.75, and +1.D., as shown in Fig. 3a.

[Illustration: 3-A—Outer spherical reel containing Cx. sphericals from
.025 to 1.00D and a blank.]

[Illustration: 3-B—Inner spherical disk containing Cx. sphericals,
automatically turns within 3-A.]

[Illustration: 3-C—Supplementary spherical disk.]

By means of a concealed tooth gear, an inner disk is automatically
picked up, placing its first lens +1.25D in position (Fig. 3b). This
+1.25D spherical lens remains stationary while the outer disk again
revolves, adding to it the original +.25, +.50, +.75 and +1.D.,
the latter totalling +2.25D. At this point, the instrument again
automatically picks up its inner disk, thereby placing its second lens,
+2.50D, in position.

[Illustration: Fig. 4—With the reappearance of “00” at sphere
indicator, a rapid increase or decrease of +1.25 is accurately and
speedily attained.]

Instead of using intermediate strengths in making an examination, it is
frequently desirable to make such extended changes as 1.25D to 2.50D.
With the Ski-optometer, the refractionist will note that two white
zeros appeared at the spherical register in connection with +1.25, and
again with +2.50. A rapid outward turn of the spherical reel toward the
temporal side to the point of the reappearance of the two zeros will
show +3.75D; or, if increased power is still desired, a rapid turn will
draw +5.D. into position (Fig. 4).

Turning the reel inward toward the nasal side will likewise decrease
its convex power. In brief, each one of these lenses, showing their
foci in conjunction with the two white zeros, are signals indicating
the rapid increase or decrease of one and one-quarter diopter. After
continuing to +6D., the next turn automatically shows zero (or
“plano”), the original starting point, which is again indicated by the
three white zeros.

Through the turn of the single reel—an exclusive Ski-optometer
feature—all convex spherical lenses have now been attained in quarters
up to +6.D, practically covering ninety percent of all refraction cases.

[Illustration: Fig. 5—With supplementary disk pointer set at +6 Sph.,
this places an additional +6.D spherical lens at sight opening,
extending instrument’s total convex spherical power to +12.D.]

Should still greater power be desired, the small pointer at the outer
edge of the instrument should be set at +6 sphere (Fig. 5). This
controls a supplementary disk (Fig. 3c) which places an additional
+6D. lens before the original range of lenses previously referred to,
thus increasing the maximum power to +12D. If still greater strength
is required, any additional trial-case lens may be added, a cell being
provided for that purpose on the forward plate of the instrument.

OPERATES AND INDICATES AUTOMATICALLY

As previously explained, in using the Ski-optometer, it is only
necessary to remember that each outward turn of the single reel toward
the temporal side of the patient _increases_ the plus power, while the
reverse turn toward the patient’s nose _decreases_ it. In fact, no
attention need ever be given the register until the required sum-total
is secured, it only being necessary to turn the single reel in order to
be assured of the unvarying and accurate operation of the instrument.

For convenience, the contour or upper edge of the plate covering the
spherical reel has been made to fit the index finger (Fig. 3). Hence
the operator should note that it requires but one complete turn from
extreme side to side, rather than a number of short turns, in order
to bring each individual lens into position, thus obtaining the full
advantage of the automatic spring-stop. This likewise permits the
refractionist to operate the Ski-optometer even though the room is in
total darkness.

CONCAVE SPHERICAL LENSES

Another simple and exclusive Ski-optometer advantage worthy of note is
the method employed in obtaining concave, spherical lenses. Instead of
employing a battery of concave lenses similar to the convex battery
previously described, the instrument’s operation is greatly simplified
through the use of a neutralizing process.

In short, the Ski-optometer only contains two concave lenses to obtain
its entire series—namely, a -6.D and a -12.D sphere (Fig. 3c)—first
setting the pointer of the supplementary disk at -6. sphere, then
setting the indicator of the spherical battery at +6.

Thus zero (or plano) is obtained, the plus neutralizing the minus.

By merely turning the plus or convex spherical reel inward, or toward
the patient’s nose, the convex power is then decreased, naturally
increasing the concave value or total minus lens power. For example,
if the spherical indicator shows +5.D, when the -6D. lens is placed
behind it, the lens value at the sight opening will be -1D (Fig. 6). If
required, the refractionist may continue on this plan until only the
-6D. lens remains.

[Illustration: Fig. 6—With this indicator of supplementary disk, set at
-6.D. Sph. and spherical indicator at +5.D—lens value at sight opening
is -1.D. Sph. This simple arrangement makes it possible to operate the
Ski-optometer with but Single Reel for both plus and minus sphericals.]

Should concave power stronger than -6D. be desired, by placing the
pointer of the supplementary disk at -12D. Sph. and proceeding to
neutralize as before, all the concave powers up to -12D. in quarters
are similarly obtained. For the convenience of the operator, all minus
or concave spherical powers are indicated in _red_; while plus, or
convex powers, are indicated in _white_.

The instrument is also provided with an opaque or blank disk which is
brought into position before the sight opening by setting the pointer
of the supplementary disk at “shut” (Fig. 3c.)

Summing up, all plus and minus spherical powers have been attained from
zero to 12D. in quarters, practically through the turn of the single
reel—_a simplicity of operation largely responsible for Ski-optometer
supremacy_.

CHAPTER II

CYLINDRICAL LENSES

It is commonly admitted that setting each trial-case cylindrical lens
at a common axis is the most tedious part of refraction.

The automatic cylinder, one of the Ski-optometer’s latest and
distinctly exclusive features, not only overcomes this annoyance but
also avoids the need of individually transferring each cylindrical lens
according to the varying strengths.

[Illustration: Fig. 7—Once you set the axis indicator as shown by
dotted fingers, each cylindrical lens in the instrument automatically
positions itself exactly at that axis, as indicated by the arrow.]

By merely setting the Ski-optometer’s axis indicator (Fig. 7), each
cylindrical lens in the instrument automatically positions itself, so
that it will appear at the opening at the _exact axis_ indicated.

This is readily accomplished by placing the thumb on the small knob, or
handle of the axis indicator, drawing it outward so as to release it
from spring tension. The indicator may then be set at any desired axis;
and, on releasing the handle, every cylinder in the instrument becomes
locked, making it _impossible_ for any lens to appear at an axis other
than the one specified by the indicator.

This insures the _absolute accuracy_ of the axis of every cylinder
as it appears before the patient’s eye. Subsequent shifting of the
axis even to a single degree is impossible, although it is a common
occurrence where trial-case lenses are employed.

OBTAINING CORRECT FOCUS

After setting the axis indicator, the only remaining move is to
obtain the correct cylindrical strength or focus. This is readily
accomplished by merely turning the Ski-optometer’s larger or extreme
outer single reel, which contains concave cylindrical lenses from .25D
to 2D in quarters (Fig. 8a). It should again be borne in mind that
a downward turn _increases_ concave cylinder power, while an upward
turn _decreases_ it. The operation of the cylinder reel is greatly
facilitated by carefully noting position of thumb and index finger
(Fig. 8). Thus accuracy of result, simplicity of operation and the
saving of much valuable time is invariably assured.

[Illustration: Fig. 8A—Inner cog-wheel construction, showing
arrangement of Ski-optometer cylinders. This simple construction
assures accuracy and avoidance of the slightest shifting of axes.]

As each cylinder appears before the patient’s eye, it simultaneously
registers its focus at the indicator marked “CC CYL” shown in Fig. 8.
Examinations of greater accuracy could not possibly be made than those
obtained through the Ski-optometer, hence no refractionist should
hesitate to employ it throughout an _entire_ examination—wherever
trial-case lenses are used.

The range of the Ski-optometer’s cylinder lens battery includes up to
2D. in quarters. An axis scale and a cell is located at the back of
the instrument for insertion of an additional trial-case cylinder
lens, when stronger cylindrical power is required. For example, if
an additional -2D. cylinder is added, it will increase the range up
to 4D. cylinder; or if twelfths are desired, a 0.12D. cylinder lens
may be inserted. In this connection, it is interesting to note that
considerable experimenting with _twelfths_ in the Ski-optometer proved
them to be needless, inasmuch as the instrument’s cylindrical lenses
set directly next to the patient’s eyes overcome all possible loss of
refraction, as explained in a later paragraph.

[Illustration: Fig. 8—Turn this Single Reel as shown by dotted finger
to obtain cylindrical lenses, which simultaneously register their focus
as they appear. Each lens also automatically positions itself at axis
designated].

WHY CONCAVE CYLINDERS ARE USED EXCLUSIVELY

The Ski-optometer contains only concave cylinders, as it is universally
admitted that convex cylinders are not essential for testing purposes.

In fact, concave cylinders should alone be used in making an
examination, even where a complete trial-case is employed. To repeat
one of the first rules of refraction: “As _much_ plus or as _little_
minus spherical power as patients will accept, combined with weakest
minus cylinder, simplifies the work of refraction and insures accuracy
without time-waste.”

After an examination with the Ski-optometer is completed, the total
result of plus sphere and minus cylinder may be transposed if desired,
though in most instances it is preferable to prescribe the exact
findings indicated by the instrument. This will also avoid every
possibility of error, eliminating responsibility where one is not
familiar with transposition—since, after all, it is the duty of the
optician to thoroughly understand that part of the work.

TRANSPOSITION OF LENSES

It is commonly understood that transposition of lenses is merely change
of form, but not of value.

For example, a lens +1.00 sph. = -.50 cyl. axis 180° may be transposed
to its equivalent, which is +.50 sph. = +.50 cyl. axis 90°. The
accepted formula in this special instance is as follows: Algebraically
add the two quantities for the new sphere, retain the power of the
original cylinder, but change its sign and reverse its axis 90 degrees.
Applying this rule, a lens +.75 sph. = -.25 cyl. axis 180°, is
equivalent to +.50 sph. = +.25 cyl. axis 90°.

Similarly, a lens +1.00 sph. = -1.00 cyl. axis 180° is equivalent to
+1.00 cyl. axis 90°.

One of the difficulties in transposing is in reversing the axis. In
such cases, it is well to memorize the following simple rule:

To reverse the axis of any cylindrical lens containing three
numerals—add the first two together and carry the last. For example,
from 105 to 180 degrees, etc.:

105° Add—one and “0” equals 1 Then carry the 5 = 15°
120° Add—one and two equals 3 Then carry the 0 = 30°
130° Add—three and one equals 4 Then carry the 0 = 40°
150° Add—five and one equals 6 Then carry the 0 = 60°
165° Add—six and one equals 7 Then carry the 5 = 75°
180° Add—eight and one equals 9 Then carry the 0 = 90°

To transpose where there are but _two_ numerals,
90° should be added.

In using the Ski-optometer, it is absolutely unnecessary to transpose
the final result of an examination; merely write the prescription
as instrument indicates. The idea that plus sphere combined with
minus cylinder, or the reverse, is an incorrect method of writing a
prescription, has long since been disproved.

CHAPTER III

HOW THE SKI-OPTOMETER ASSISTS IN REFRACTION

The construction of the Ski-optometer has now been fully explained, and
the reader realizes that since the instrument contains all the lenses
necessary in making an examination, greater operative facility is
afforded through its use than where the trial-case lenses are employed.

The Ski-optometer is “an automatic trial-case” in the broadest sense
of the term, wholly superseding the conventional trial-case. It should
therefore be employed throughout an entire examination, wherever
trial-case lenses were formerly used. To fully realize its labor saving
value in obtaining accurate examination results, it is only necessary
to recall the tedious method of individually handling and transferring
each lens from the trial-case to the trial-frame, watching the stamped
number on each lens handle, wiping each lens and in the case of
cylindrical lenses setting each one at a designated axis—all being
needless steps where the Ski-optometer is employed.

THE USE OF THE SKI-OPTOMETER IN SKIOSCOPY

In skioscopy, the Ski-optometer offers the refractionist assistance of
the most valuable character.

For example, assuming that extreme motion in the opposite direction
with plane or concave mirror is obtained with a +1.25D. spherical
lens before the patient’s eye; by quickly turning the Ski-optometer’s
single reel until the two white zeros again appear, +2.50D is secured,
as explained in the previous chapter. If this continues to give too
much “against motion,” the lens power should be quickly increased to
+3.75 or +5.00D if necessary (Fig. 4). Should the latter reveal a
shadow in the reversed direction, the refractionist is assured that it
is the weakest lens that will cause its neutralization. Practically
but few lenses have been used to obtain the final result proving
the instrument’s importance and time-saving value in skioscopy, and
demonstrating the simplicity with which tedious transference of
trial-case lenses is avoided.

Furthermore, it should be noted that where the Ski-optometer is used
in skioscopy, it is not necessary to remove the retinoscope from the
eye or to constantly locate a new reflex with each lens change. This
permits a direct comparison of the final lens and eliminates the usual
difficulty in mastering skioscopy. The chief cause of this difficulty
is due to the fact that the transferring of the trial-case lenses makes
it practically impossible for the student to determine whether the
previous lens caused more “with” or “against” motion.

[Illustration: Fig. 9—The Woolf ophthalmic bracket. A convenient and
portable accessory in skioscopy and muscle testing; can be used with or
without Greek cross.]

Where the indirect method is employed in skioscopy, best results
are secured through the use of the Woolf ophthalmic bracket and
concentrated filament lamp, together with an iris diaphragm chimney.
The latter permits the reduction or increase of the amount of light
entering the eye, as it is agreed that a large pupil requires _less_
light, a small pupil requiring _more_ light. The bracket referred to
permits the operator to swing the light into any desired position
(Fig. 9), while the iris diaphragm chimney serves as a shutter. This
apparatus may also be employed for muscle testing, as described in a
subsequent paragraph.

A SIMPLIFIED SKIOSCOPIC METHOD

In using the Ski-optometer, instead of working forty inches away from
the patient in skioscopy and deducting 1.D., the refractionist will
find it more convenient to work at a twenty inch distance, deducting
2.D. This working distance may be accurately measured and maintained by
using the reading rod accompanying the instrument. Instead of deducting
2.D. from the total findings, however, it is preferable to insert a
+2.D. trial-case lens in the rear cell of the instrument directly next
to the patient’s eye. After determining the weakest lens required to
neutralize the shadow in both meridians, the additional +2.D. lens
should be removed and the total result of the examination read from the
instrument’s register.

To illustrate a case in skioscopy where spherical lenses are employed
to correct both meridians, assume that the vertical shadow requires
a +1.25D lens to cause its reversal, while the horizontal requires
+2.00D. Employment of the customary diagram, illustrated in Fig. 10,
would show the patient required +1.25 sph. = +.75 cyl. axis 90°, which
when transposed is equivalent to +2.00 sph. = -.75 cyl. axis 180°.

[Illustration: Fig. 10—Where spherical lenses are employed in
skioscopy, above indicates patient requires]

+1.25 Sph. = +.75 Cyl. Axis 90°
or +2 Sph. = -.75 Cyl. Axis 180°

It should be noted that the total spherical power is +2.00D, as the
Ski-optometer’s register shows, while the difference between the two
meridians is 75, which is the required strength of the cylinder. By
then turning the cylinder reel to .75, and setting the axis indicator
at 180° (because by using minus cylinders, the axis must be reversed)
the patient should read the test-type with ease if the skioscopic
findings are correct. Thus with the Ski-optometer, it is not even
necessary to learn transposition, since the instrument automatically
accomplishes the work, avoiding all possibility of error.

EMPLOYING SPHERES AND CYLINDERS IN SKIOSCOPY

Another commonly used objective method may be employed with even
greater facility through the combined use of both the Ski-optometer’s
spherical and cylindrical lenses. As previously suggested, insert the
+2.00 spherical trial-case lens in the rear of the instrument, working
at a twenty inch distance, then proceed to correct the strongest
meridian first.

It was assumed that it required a +2.00 spherical to neutralize
the strongest, or horizontal meridian, as shown in Fig. 10. The
refractionist should then set the axis indicator therewith, which is
the axis of the cylinder, or 180°.

It is then merely a matter of increasing the Ski-optometer’s
cylindrical lens power until the reversal of the shadow in the weakest
meridian is determined. Assuming this proves to be -.75 cylinder, axis
180°, the patient’s complete prescription +2.00 sph. = -.75 cyl. axis
180°, would be registered in the Ski-optometer without any further lens
change other than the removal of the +2.00 working distance lens.

However, regardless of the method employed, the Ski-optometer greatly
simplifies skioscopy. In fact, the instrument was originally intended
to simplify retinoscopy or skioscopy, as the subject should be termed,
the name “Ski-optometer” having been derived from the latter.

USE OF THE SKI-OPTOMETER IN SUBJECTIVE TESTING

In subjective refraction, especially where the “better or worse”
query must be decided by the patient, it is commonly understood that
the refractionist is compelled to first increase and then decrease
a quarter of a diopter before the final lens is decided. With the
Ski-optometer, the usual three final changes are made in far less
time than it takes to make even _one_ lens change from trial-case to
trial-frame.

For example:

Assuming, with a +1.25D spherical lens before the patient’s right
eye, he remarks that he “sees better” with a +1.D. while +.75D is not
as satisfactory. The refractionist can then quickly return to +1.D.,
simply turning the Ski-optometer’s single reel _outward_ to increase,
or _backward_ to decrease, the lens strength. So rapidly have these
lens changes been made, that the patient quickly sees the difference of
even a _quarter_ diopter, and quickly replies, “better” or “worse.”

This is made possible because the eye does not “accommodate” as quickly
as the lens change made with the Ski-optometer. It should also be noted
that the eye receives an image on its retina within one-sixteenth of
a second; otherwise, the patient is forced to accommodate, making it
difficult to see the difference of even a quarter diopter. On the
other hand, in transferring trial-case lenses, with its slow, tedious
procedure, the patient, being unable to detect the slight difference of
only a quarter diopter, unhesitatingly replies, “no difference,” merely
because they are compelled _to accommodate_.

A SIMPLIFIED SUBJECTIVE METHOD

The following simplified method of procedure is suggested for
subjective testing with the Ski-optometer, although as previously
explained, the refractionist may employ his customary method,
overcoming the annoyance of transferring trial-case lenses and the
setting of each cylinder individually. The Ski-optometer has been
constructed and based upon the golden rule of refraction: “As much plus
or as little minus spherical, combined with as little minus cylinder
power as the patient accepts.”

By applying this rule as in the above method and starting with +5.D.
spherical, watching the two zeros (Fig. 4) and rapidly reducing +1.25D
each time, we will assume that +1.25D gives 20/30 vision; as a final
result +1.D. will possibly give 20/25 vision.

The patient’s attention should next be directed to the most visible
line of type, preferably concentrating on the letter “E” or the clock
dial chart—either of which will assist in determining any possible
astigmatism. Since the Ski-optometer contains concave cylinders
exclusively, the next move should be the setting of its axis indicator
at 180°, commonly understood as “with the rule.” One should then
proceed to determine the cylinder lens strength by turning the reel
containing the cylindrical lenses (Fig. 8). Should the patient’s vision
fail to improve after the -.50D. cylinder axis 180° has been employed,
the refractionist, in seeking an improvement, should then slowly move
the axis indicator through its entire arc.

With the cylinder added, regardless of axis, poor vision might indicate
the absence of astigmatism. If astigmatism exists, vision will usually
show signs of improvement at some point, indicating the approximate
axis. Once the latter is ascertained, the refractionist may readily
turn the Ski-optometer’s cylinder reel and obtain the correct cylinder
lens strength, after which the axis indicator should be moved in either
direction in order to obtain the best possible vision for the patient.

The refractionist should always aim to obtain normal (or 20/20) vision
with the weakest concave cylinder, combined with the strongest plus
sphere, or weakest minus sphere.

PROCEDURE FOR USING MINUS CYLINDERS EXCLUSIVELY

For the benefit of those who have never used minus cylinders
exclusively in making their examinations, we will assume that the
patient requires O.U. +1.D sph. = -1D cyl. axis 180° for final
correction; the latter, in its transposed form, being equivalent to
+1.D. cylinder axis 90°. Unquestionably the best method is the one that
requires the least number of lens changes to secure the final result.

To obtain this, the following order of lens change should be made:
First, +1.D. sphere is finally determined and allowed to remain in
place. Concave cylinders are then employed in quarters until the final
results of +1.D. spherical, combined with -1.D. cylinder axis 180° is
secured. This necessitates the change of but _four_ cylindrical lenses
as shown in routine “A” as follows:

ROUTINE “A” ROUTINE “B”
(Made with _minus_ cylinder) (Made with _plus_ cylinder)

Sph. +1.D. Cyl. Axis Sph. +1.D. Cyl. Axis
Step 1 +1.D. = -.25 ax. 180° equal to +.75 = +.25 ax. 90°
Step 2 +1.D. = -.50 ax. 180° equal to +.50 = +.50 ax. 90°
Step 3 +1.D. = -.75 ax. 180° equal to +.25 = +.75 ax. 90°
Step 4 +1.D. = -1 ax. 180° equal to 0 +1 ax. 90°

In brief the method of using minus cylinders exclusively in an
examination, as explained in routine “A”, necessitates the change of
the cylinder lenses only after the _strongest_ plus sphere is secured.

On the other hand, notwithstanding innumerable other methods where plus
cylinders are used, routine “B” shows that the best spherical lens
strength the patient will accept, is also first determined. Then both
spheres and cylinders are changed in their regular order by gradually
building up in routine, by increasing plus cylinder and next decreasing
sphere, a quarter diopter each time, until the final result is secured.

While it is conceded that both routine “A” and “B” are of themselves
simplified methods, by comparing routine “A” where minus cylinders
are used with routine “B” where plus cylinders are used in their
corresponding steps, the refractionist will note by comparison that
one is the exact equivalent and transposition of the other. Where
_plus_ cylinders are employed, eight lens changes are made before final
results are secured; while but four lens changes are necessary where
_minus_ cylinders are used.

The refractionist should also note by comparison that the use of minus
cylinders reduces focus of the plus sphere, but only in the meridian
of the axis. It has not made the patient myopic. Furthermore, a plus
cylinder will bring the focal rays forward, while minus cylinders throw
them backward toward the retina.

This is but another reason for the exclusive use of minus cylinders in
refraction.

The method of using _minus cylinders_ exclusively in an examination,
necessitates the change of the cylinder lenses _only_. On the other
hand, the method of using plus cylinders makes it necessary to change
spheres and cylinders in routine.

In brief, since using the minus cylinder is merely a matter of
mathematical optics, their use even in a trial-case examination is
strongly urged.

The maximum value of the Ski-optometer is fully realized only when the
advantages of using minus cylinders exclusively in every examination is
clearly understood.

CONSTANT ATTENTION NOT REQUIRED

With the Ski-optometer, when the examination is completed, the
sum-total of final results—whether spherical, cylinder, axis, or all
combined—are automatically indicated or registered ready to write the
prescription. _Until then_, the foci of the various lenses that may be
employed are of no importance.

In short, in using the Ski-optometer, it is not necessary to constantly
watch the registrations during examinations. The automatic operation
of the instrument is an exclusive feature, so that the refractionist
should unhesitatingly employ it. Hence, by eliminating the perpetual
watch on the lenses in use, the refractionist is enabled to give his
undivided attention to the patient rather than to the trial lenses.

Where a special dark-room is used for skioscopic work, an additional
wall bracket or floor stand will necessitate only the removal of
the instrument itself. This enables the refractionist to use the
Ski-optometer for subjective or objective work, without disturbing the
patient’s correction.

CHAPTER IV

IMPORTANT POINTS IN CONNECTION WITH THE USE OF THE SKI-OPTOMETER

The Ski-optometer is equipped with an adjustable head-rest, permitting
its lenses to be brought as close as possible to the eye without
touching the patient’s lashes, a matter of importance in every
examination.

[Illustration: Fig. 11—The nasal lines of the Ski-optometer fit the
contour of face with mask-like perfection, patient remaining in
comfortable position.]

ELIMINATION OF TRIAL-FRAME DISCOMFORT

Where the Ski-optometer is correctly fitted to the face, the patient
invariably remains in a comfortable position (Fig. 11). The instrument
is shaped to fit the face like a mask, so that even with a pupillary
distance of but 50 m/m (that of a child) there still remains, without
pinching, ample room for the widest nose of an adult.

Before making an examination, the correct pupillary distance should
always be obtained by drawing an imaginary vertical line downward
through the center of each eye from the 90° point on the Ski-optometer
axis scale. The pupillary distance will then register in millimeters on
the scale of measurements for each eye separately. If the Ski-optometer
is correctly adjusted, the patient is securely held in position, the
cumbersome trial-frame being entirely eliminated.

RIGIDITY OF CONSTRUCTION

Illustration on following page (Fig. 11a) shows the reinforced double
bearing arms which hold the Ski-optometer lens batteries at two points.
This eliminates possibility of the instrument getting out of alignment,
and prevents wabbling or loose working parts.

The broad horizontal slides shown in the cut, move in and out
independently so that the pupillary distance is obtained for each
eye separately by turning the pinioned handle on either side of the
instrument. The scale denotes in millimeters the P.D. from the median
line of the nose outward, the total of both scales being the patient’s
pupillary distance.

Fig. 11a also serves to show the staunch construction of the base of
the Ski-optometer.

[Illustration: Fig. 11a—Showing staunch construction of Ski-optometer
base.]

HOW TO PLACE THE SKI-OPTOMETER IN POSITION

The patient should be placed in a comfortable position with “chin up,”
as though looking at a distant object. The instrument should then be
raised or lowered by the adjustable ratchet wheel of the bracket. The
wall bracket gives best results when suspended from the wall, back
of the patient, as shown on page 135. This bracket should be placed
about ten inches above the head of the average patient. When the
Ski-optometer is placed in position for use, its lower edge will barely
touch the patient’s cheeks. It is sometimes advisable to request the
patient to lightly press toward the face the horizontal bar supporting
the instrument. Particularly good results are secured where a chair
with a head-rest is employed in conjunction with the Ski-optometer.
(See illustration of Model Refraction Room, Page 112).

CLEANING THE LENSES

The time-waste of perpetually cleaning lenses is overcome where the
Ski-optometer is employed. For the convenience of the operator and
protection of Ski-optometer lenses, the latter are concealed in a
dust-proof cell, overcoming all dust and finger-print annoyances. When
not in use, the instrument should be covered with the standardized hood
forming part of the equipment.

The instrument should not be taken apart under any circumstances. To
clean its lenses, not a single screw need be removed, as the lenses of
each disk may be cleaned individually through the opening of the other
disks. These openings are conveniently indicated by the white zeros
(Fig. 2). The Ski-optometer contains but eleven spherical and eight
cylindrical lenses on each side, so that the actual work of cleaning
should not require over ten minutes at the most, cleaning the lenses
every other week proving quite sufficient.

ACCURACY ASSURED IN EVERY TEST

Loss of refraction is completely eliminated through the use of the
Ski-optometer. The most casual examination of the trial-frame or
any other instrument shows that the construction necessitates the
placing of the spherical lens next to the eye with the cylinder lens
outermost—a serious fault wholly overcome in the Ski-optometer.

Not only do the cylindrical lenses of the Ski-optometer set directly
next to the patient’s eye, thus overcoming any possible loss of
refraction, but the strong spherical lenses of the supplementary disk
are set directly next to the cylinder. There is apparently but a hair’s
distance between these lenses; the two disks containing the spherical
lenses of the Ski-optometer likewise setting close together.

In a word, the Ski-optometer’s cylinder lenses set directly next to the
patient’s eye, followed by the stronger sphericals, so that the weakest
spherical or +.25 (the lens of least importance) sets farthest away.
This is 3½ m/m closer than any trial-frame manufactured, however, and
at least 10 m/m closer than any other instrument—another reason for
implicitly relying on the Ski-optometer for uniformly accurate results.

BUILT TO LAST A LIFETIME

[Illustration: Fig. 12—(A. and B.)—This unique, patented split-spring
device of screwless construction, securely holds all movable parts. In
case of repair, they may be removed with the blade of a knife.]

The Ski-optometer is built on the plan of ¹/₁₀₀₀″, insuring absolute
rigidity and accuracy and a lifetime of endurance. Particular and
detailed attention has been given to the novel means of eliminating
screws which either bind, create friction or continually work loose,
causing false indications of findings on scales of measurements; hence
correct and accurate indications are insured in the Ski-optometer by
means of a split-spring washer construction similar to that of an
automobile tire’s detachable rim (Fig. 12).

This patented spring washer construction securely holds the phorometer
lenses, the rotary prism and the revolving cylinder lens cells.

Whenever necessary, or in case of repair, these parts may be readily
removed with the blade of a knife.

CHAPTER V

CONDENSED PROCEDURE FOR MAKING SPHERE AND CYLINDER TEST WITH THE
SKI-OPTOMETER

Notwithstanding various methods employed, for both subjective and
objective refraction, the following synopsis of the previous chapters
will unquestionably prove most valuable to the busy refractionist,
enabling him to make error-proof examinations in practically every case
without resorting to the transference of trial-case sphere or cylinder
lenses. A careful reading of chapters one and two should be made
however, so that one may gain an understanding as to how spheres and
cylinders are obtained with the Ski-optometer.

SUBJECTIVE DISTANCE TEST

1st—Place Ski-optometer in position, employing spirit level, thus
maintaining instrument’s horizontal balance.

2nd—Adjust the pupillary distance for each eye individually, by drawing
an imaginary vertical line downward through the center of each eye from
the 90° point on the Ski-optometer’s axis scale. The opaque disk should
be placed before the patient’s left eye by setting the supplementary
disk handle at “shut.”

3rd—The Ski-optometer lens battery before the patient’s right eye
should be set at “open” (figure 2), whereupon the first turn of
spherical lens battery toward the nasal side places a +6.D sphere in
position. This should blur vision of average patient.

4th—It is now only necessary to remember that an outward turn toward
temporal side of the instrument increases plus sphere power, while
a nasal turn decreases it. Therefore continue to reduce convex
spherical lens power until the large letter “E” on the distant test
card is clear. Then request patient to read as far down as possible,—a
rapid turn of a quarter diopter being readily accomplished with the
Ski-optometer (Fig. 4).

5th—In the event of working down to “zero” with spheres, the
supplementary disk handle or indicator should next be set at -6.D
sphere, while the spherical reel should be turned toward the nasal
side—thus building up on minus spheres (Fig. 6). In short, the
strongest plus sphere or weakest minus sphere should always be
determined before employing cylinders.

6th—With the best spherical lens that the patient will accept left in
place, direct attention to the letter E or F in the lowest line of
type the patient can see on the distant test letter chart. Then set
axis indicator at 180° (Fig. 7).

7th—Next increase concave cylinder power until vision is improved. If
vision is not improved after increasing cylinder strength to -.50 axis
180°, merely reverse the axis to 90°. If vision is improved, cylinder
lens strength should be increased. If not, it should be decreased (Fig.
8).

8th—Slowly move axis indicator through entire arc of axis, thus
locating best possible axis (Fig. 7).

9th—After sphere and cylinder test of right eye has been made, place
supplementary disk handle at “shut.” Then repeat procedure in testing
left eye.

10th—After completing examination for each eye separately, then, with
both of the patient’s eyes open, direct attention to lowest line of
type he can see, concentrating on the E or F, simultaneously increasing
or decreasing spherical power before both eyes. The refractionist
merely recalls that by turning the Ski-optometer’s single reel toward
the temporal side, convex spherical power is increased, by turning
toward the nasal side for either eye, spherical power is decreased.
Cylinder lens strength may be changed in a like manner before both eyes
simultaneously.

11th—After making the distance test, then only is it necessary to copy
the result of the examination as recorded by the Ski-optometer.

SUBJECTIVE READING TEST

Tilt Ski-optometer forward in making reading test. The wide groove in
the horizontal bar supporting the instrument, permits it to be slightly
tilted.

12th—Place Ski-optometer reading rod in position with card at about
14 inches. Close off one eye. Direct patient’s attention to the name
“Benjamin” printed at top of card.

13th—Leave cylinder lens in place. Proceed as in distance test with
+6.D sphere, fogging down until the first word “laugh” on the reading
card, in line 75M, is perfectly clear, this being slightly smaller than
the average newspaper type.

14th—After completion of examination for each eye separately, then with
both eyes direct patient’s attention to word “laugh.” Move reading card
in or out a few inches either side of 14 inch mark. This will determine
any possibility of an over-correction. Then record prescription just as
Ski-optometer indicates. For a detailed description of above, as well
as for objective testing with the Ski-optometer, read chapter three.

CHAPTER VI

MUSCULAR IMBALANCE

The purpose of the present chapter is to acquaint the refractionist
with the operation of the Ski-optometer as “a scientific instrument
for muscle testing”—the subject being treated as briefly and
comprehensively as is practicable.

As the reader progresses in the subject of muscular anomalies, he
may carry his work to as high a plane as desired, increasing his
professional usefulness to an enviable degree.

Through the use of the Ski-optometer, muscle testing may be accurately
accomplished in less time than a description of the operation requires.
Furthermore, tedious examinations may be wholly overcome through the
discontinuance of the consecutive transference of the various degrees
of prisms from the trial-case. In fact, the latter method has long been
quite obsolete, owing to the possibility of inaccuracy. The muscle
action of the eye is usually quicker than the result sought through the
use of trial-case prisms; hence muscle testing with the Ski-optometer
is accomplished with far greater rapidity and accuracy, thus making the
instrument an invaluable appliance in every examination.

THE ACTION OF PRISMS

Students in refraction—and one may still be a student after years of
refracting—are sometimes puzzled as to just what a prism does when
placed before an eye. They refer to every available volume and are
often confused between ductions and phorias, finally dropping the
subject as an unsolvable problem. In view of this fact, it is suggested
that the refractionist should read the present volume with the actual
instrument before him.

Before proceeding, one should first understand the effect of a prism
and what it accomplishes. To determine this, close one eye, looking at
some small, fixed object; at the same time, hold a ten degree prism
base in before the open eye, noting displacement of the object. This
will clearly show that the eye behind the prism turns toward the prism
apex.

To carry the experiment further, the following test may be employed on
a patient. Covering one eye, direct his attention to a fixed object,
placing the ten degree prism before the eye, but far enough away to
see the patient’s eye behind it. As the prism is brought in to the
line of vision, it will be seen that the eye turns towards the apex of
the prism. When the prism is removed, the eye returns to its normal
position.

Similar experiments enable the refractionist to make the most practical
use of treating phorias and ductions, as well as to comprehend all
other technical work.

[Illustration: Fig. 13—An important part of the equipment for muscular
work.]

THE PHOROMETER

As previously stated, it is practically impossible to accurately
diagnose a case of muscular imbalance with trial-case prisms. For this
reason the phorometer forms an important part of the equipment for
muscle testing in the Ski-optometer, having proven both rapid and
accurate. It consists of two five-degree prisms with bases opposite,
each reflecting an object toward the apex or thin edge. The patient
whose attention is directed to the usual muscle-testing spot of light,
will see _two_ spots.

Aside from the instrument itself, and in further explanation of the
phorometer’s principle and construction, when two five-degree prisms
are placed together so that their bases are directly opposite, they
naturally neutralize; when their bases are together, their strength is
doubled. Thus while the prisms of the phorometer are rotating, they
give prism values from plano to ten degrees, the same being indicated
by the pointer on the phorometer’s scale of measurements.

As a guide in dark-room testing, it should be noted that the handle
of the phorometer in a vertical position is an indication that the
vertical muscles are being tested; if horizontal, the horizontal
muscles are undergoing the test.

THE MADDOX ROD

The Maddox rod (Fig. 14) consists of a number of red or white rods,
which cause a corresponding colored streak to be seen by the patient.
This rod is placed most conveniently on the instrument, being provided
with independent stops for accurately setting the rods at 90 or 180
degree positions. The Maddox rod has proven of valuable assistance in
detecting muscular defects, particularly when used in conjunction with
the phorometer. Thus employed, it enables the patient to determine
when the streak seen with one eye crosses through the muscle-testing
spot-light observable by the other eye, as hereafter described.

[Illustration: Fig. 14—The Maddox Rod, a valuable aid in making
muscular tests.]

PROCEDURE FOR MAKING THE MUSCLE TEST

The Ski-optometer should be equipped with _two_ Maddox rods, one red
and one white. Their combined use is of the utmost importance since
they assist in accurately determining cyclophoria and its degree of
tortion as designated on the degree scale, and fully described in a
later chapter.

When the Maddox rods are placed in a vertical position, it is an
indication that the vertical muscles are being tested; when placed
horizontally, the horizontal muscles are being tested. It should be
particularly noted that the streaks of light observable through the
Maddox rods always appear at right angles to the position in which they
lie.

The Ski-optometer should be placed in a comfortable position before
the patient’s face with the brow-rest and pupillary distance adjusted
to their respective requirements. The instrument should be levelled so
that the bubble of the spirit level lies evenly between its two lines,
thus insuring horizontal balance. The muscle test light should be
employed at an approximate distance of twenty feet on a plane with the
patient’s head. Best results in muscle testing are secured through the
use of the Woolf ophthalmic bracket, with iris diaphragm chimney and a
specially adapted concentrated filament electric lamp (Fig. 9). This
gives a brilliant illumination which is particularly essential. The
test for error of refraction should be made in the usual manner, using
the spherical and cylindrical lenses contained in the Ski-optometer,
thus obviating the transference of trial-case lenses and the use of
a cumbersome trial-frame. The time-saving thus effected enables the
refractionist to include a muscle test in every examination and without
tiring the patient—a consideration of the utmost importance.

BINOCULAR AND MONOCULAR TEST

The test for muscular imbalance may be divided in two parts. First,
binocular test, or combined muscle test of the two eyes; second,
monocular test, or muscle test of each eye separately. The latter does
not signify the shutting out of vision or closing off of either eye,
since muscular imbalance can only be determined when both eyes are
open. These two tests are fully explained in the following chapter.

CHAPTER VII

THE BINOCULAR MUSCLE TEST

MADE WITH THE MADDOX ROD AND PHOROMETER

Directing the patient’s attention to the usual muscle testing spot of
light, the _red_ Maddox rod should be placed in operative position
before the eye, with the single _white_ line or indicator on red zero
(Fig. 15). The rods now lie in a vertical position.

[Illustration: Fig. 15—The Maddox rods placed vertically denote test
for right or left hyperphoria, causing a horizontal streak to be seen
by patient.]

The pointer of the phorometer should likewise be set on the neutral
line of the red scale, causing the handle to point upward (Fig. 16).
A distance point of light and a red streak laying in a horizontal
position should now be seen by the patient.

[Illustration: Fig. 16—The phorometer handle placed vertically, denotes
vertical muscles are undergoing test for right or left hyperphoria—as
indicated by “R. H.” or “L. H.”]

Instead of memorizing a vast number of rules essential where trial
case prisms are employed for testing ocular muscles, the pointer of
the phorometer indicates not only the degree on the red scale, but the
presence of right hyperphoria (R. H.) or left hyperphoria (L. H.).

[Illustration: Fig. 17—The horizontal streak caused by Maddox rod
bisecting muscle testing spot-light for vertical imbalance, as patient
should see it.]

Assuming that the patient finds that the streak _cuts through_ the
point of light, the refractionist instantly notes the absence of
hyperphoria. Should the point of light and the red streak _not_ bisect,
prism power must be added by rotating the phorometer’s handle to a
position that will cause the streak to cut through the light (Fig. 17).
While testing for hyperphoria, the red scale should alone be employed,
the white scale being totally ignored.

[Illustration: Fig. 18—The Maddox rods placed horizontally test
esophoria or exophoria, causing a vertical streak to be seen by the
patient.]

ESOPHORIA AND EXOPHORIA

The next step is to set the white lines of the red Maddox rod either
at white zero, or 180° line, with the rods in a horizontal position
(Fig. 18) and the phorometer on the white neutral line, with handle
horizontal (Fig. 19), thus making the test for esophoria or exophoria,
technically known as lateral deviations.

The red streak will now be seen in a vertical position. Should it
bisect the spot of light, it would show that no lateral imbalance
exists. Should it not bisect, the existence of either esophoria or
exophoria is proven, necessitating the turning of the phorometer
handle. Should the refractionist rotate the handle in a direction
opposing that of the existing imbalance, the light will be taken
further away from the streak, indicating that the rotation of the
prisms should be reversed.

[Illustration: Fig. 19—The phorometer handle placed horizontally
denotes horizontal muscles are undergoing test for esophoria or
exophoria indicated by “Es.” or “Ex.”]

At the point of bisection (Fig. 20), the phorometer will indicate on
the white scale whether the case is esophoria or exophoria and to what
amount. In testing esophoria (ES) or exophoria (EX), the white scale is
alone employed, no attention being given to the red scale.

[Illustration: Fig. 20—The vertical streak bisecting muscle testing
spot-light for horizontal imbalance, as patient should see it.]

MAKING MUSCLE TEST BEFORE AND AFTER OPTICAL CORRECTION

It is considered best to make the binocular test _before_ regular
refraction is made, making note of the findings; and again repeating
the test after the full optical correction has been placed before the
patient’s eye. This enables the refractionist to definitely determine
whether the correction has benefited or aggravated the muscles.
Furthermore, by making the muscle test before and after the optical
correction, a starting point in an examination is frequently attained.
For example, where the phorometer indicates esophoria it is usually
associated with hyperopia, whereas exophoria is usually associated with
myopia, thus serving as a clue for the optical correction.

Assuming for example that the binocular muscle test shows six degrees
of esophoria without the optical correction, and with it but four
degrees, it is readily seen that the imbalance has been benefited by
the optical correction. Under such conditions it is safe to believe
that the optical correction will continue to benefit as the patient
advances in years, tending to overcome muscular defect.

WHEN TO CONSIDER CORRECTION OF MUSCULAR IMBALANCE

In correcting an imbalance, it is also a good plan to adhere to the
following rule: In case of hyperphoria, either right or left, consider
for further correction only those cases that show one degree or more.
In exophoria, those showing three degrees or more. In esophoria,
correct those showing five degrees or more, except in children,
where correction should be made in cases showing an excess of 3° of
esophoria. These rules are naturally subject to variation according to
the patient’s refraction and age, but they are generally accepted as
safe.

FOUR METHODS FOR CORRECTION OF MUSCULAR IMBALANCE

There are four distinct methods for correcting muscular imbalance, each
of which should be carried out in the following routine:

1. _Optical correction_ made with spheres or cylinders, or a
combination of both.

2. _Muscular exercising_ or “ocular gymnastics.” This is accomplished
on the same principle as the employment of other forms of exercises, or
calisthenics.

3. _The use of Prisms_: When the second method fails, prisms are
supplied, with base of prism before the weak muscle, for rest only.

4. _Operation_: If the above three methods, as outlined in the
following chapters, have been carefully investigated, nothing remains
but a tetonomy or advancement, or other operative means for relief and
satisfaction to the patient.

THE ROTARY PRISM

The rotary prism of the Ski-optometer, (Fig. 21) consists of a prism
unit, having a total equivalent of thirty degrees. It is composed of
two fifteen-degree prisms, back to back, so that the turn of its pinion
or handle causes each of its lenses to revolve, one on the other. When
its bases are opposite, they neutralize; when directly together, they
give a total value of thirty degrees. While revolving from zero to
maximum strength, they give prism values which are indicated on the
scale of measurements, the red line denoting the total prism equivalent.

[Illustration: Fig. 21—Turning rotary prism’s pinioned handle gives
prism value from zero to 30° as indicated by prism’s red line
indicator.]

It is obviously essential to know where the base of the rotary prism is
located. Therefore if prism in or out is desired, the zero graduations
should be placed vertically and the red line or indicator set at the
upper zero (Fig. 21).

A rotation inward to 10 would give a prism equivalent of ten degrees,
base _in_. A rotation from zero to 10 outward would give a prism
equivalent of ten degrees, base _out_, etc. With zero graduations
horizontal and the red line or indicator set therewith, a rotation
upward to ten on the scale would give a prism equivalent of ten
degrees, base _up_. A rotation from zero downward to 10 would give a
prism equivalent of ten degrees, base _down_.

An understanding of the foregoing will show that a rotation of the red
line, or indicator, will give prism value from zero to 30, with base
up, down, in or out.

USE OF THE ROTARY PRISM IN BINOCULAR MUSCLE TESTS

Should a case be one of esophoria, exceeding the ten degree range of
the phorometer, the rotary prism should be brought into operative
position with cypher (0) graduations vertical (Fig. 21), while the red
line or indicator should be set at 10 on the outer or temporal scale.
The phorometer’s indicator should again be set on the center or neutral
line on the white scale. The rotary prism will then add ten degrees to
the esophoria reading indicated on the phorometer.

Should the case be one of exophoria, exceeding ten degrees, the
indicator should be set at ten degrees upon the inner or nasal scale
and the indicator of the phorometer should then be set at the white
center or neutral line, as in the previous test. Should prism power
ever be required to supplement the phorometer in hyperphoria, the
rotary prism should be employed with zero graduations horizontal, and
the red line or indicator set at ten degrees on upper or lower scale,
as required.

CHAPTER VIII

THE MONOCULAR DUCTION MUSCLE TEST

MADE WITH BOTH ROTARY PRISMS

While the previously described binocular muscle test made with the
phorometer and Maddox rod, only determines the existence and amount
of esophoria, exophoria, and hyperphoria, neither the faulty nor
the deviating muscle is located, hence a _monocular muscle test_ is
essential in order to determine whether the muscles of the right or
left eye are faulty. Furthermore, an imbalance may possibly be due to
either a faulty muscular poise, or lack of nerve force in one or both
eyes. A “duction test” should accordingly be made of each muscle of
each eye separately, followed by a comparison of the muscular pull of
both eyes collectively.

These tests are commonly termed adduction, abduction, superduction and
subduction, and are defined in the order named. They include tests of
the vertical and horizontal muscles of each eye, made individually by
means of the rotary prisms, each being placed before the eye undergoing
the test.

LOCATING THE FAULTY MUSCLE

The phorometer and the Maddox rod should be removed from operative
position, discontinuing the use of the muscle-testing spot-light,
employed in the previously described binocular test. The optical
correction, if one is required, should be left in place, while the
patient’s attention should be directed, with both eyes open, to the
largest letter on the distant test chart; or if preferable, the Greek
cross in the Woolf ophthalmic, chimney may be used. Either one,
however, should be located on a plane with the patient’s head. As a
guide for the operator, it might be well to remember that when the
handle of the rotary prism is in a horizontal position, the lateral or
horizontal muscles are being tested. On the other hand, when the handle
is in a vertical position, the vertical muscles are undergoing the test.

ADDUCTION

Adduction, or relative convergence, is the power of the internal
muscles to turn the eyes inward; prism power base out and apex in, is
employed.

[Illustration: Fig. 22—To test adduction, base out is required. Rotary
prism’s line or indicator should be rotated from zero outwardly. To
test abduction, base in is required. Indicator should be rotated
inwardly from zero.]

To test adduction of the patient’s right eye, the rotary prism should
be placed in position before the right eye, the red line or prism
indicator being registered at zero upon the prism upper scale. The two
cyphers (0) should be placed in a vertical position with the handle
pointed horizontally (Fig. 21). The rotary prism should then be rotated
so that its red line or indicator is rotated outward from zero until
the large letter—preferably the largest letter, which is usually “E”—on
the distance test-type or the Greek cross previously referred to, first
appears to double in the horizontal plane. The reading on the scale of
measurements should accordingly be noted. This test should be repeated
several times, constantly striving for the highest prism power that the
patient will accept without producing diplopia. The prism equivalent
thus obtained will indicate the right adduction and should be so
recorded, as designated in Fig. 24. The amount of adduction ranges from
6 to 28, prism diopters, the normal average being 24.

ABDUCTION

Abduction is the relative power of the external muscles to turn
the eyes outward. Prism power base in and apex out is employed. To
determine abduction, or the amount of divergence of the external rectus
muscle of the right eye, prism power with base in or toward the nasal
side should be employed. The rotary prism will therefore remain in the
same relative position as in making the adduction test (Fig. 22), with
the two cyphers (0) or zero graduations vertical, but the indicator or
red line should be rotated _inward_ from zero, or towards the patient’s
nose.

With the patient’s attention again directed to the large letter “E,”
or the Greek cross, this inward rotation should be continued until
diplopia or double vision occurs. Like the former, this test should
be repeated several times, the refractionist continuing to strive for
the highest prism power which the eye will accept. This will indicate
abduction of the right eye and should be so recorded as designated in
Fig. 24. The amount of abduction ranges from 3 to 10 prism diopters.
The normal average is 8.

The ratio of adduction to abduction is normally rated at about three
to one. In other words, it is conceded that the power of the eye to
converge is normally three times as great as its power to diverge,
the usual measurements being eight to twenty-four respectively. While
applicable in most instances, this may vary in different cases.

SUPERDUCTION

Superduction, sometimes termed sursumduction, is the relative power of
the superior recti to turn the eyes upward. Prism power base down and
apex up is employed. To test superduction, the rotary prism should be
placed in position with the two cyphers lying horizontally, with the
handle pointed vertically (Fig. 23). The patient’s attention should
again be directed to the large letter “E”, and the indicator or red
line should be rotated downward from zero. The highest prism power that
the patient will accept before the object appears to double in the
vertical plane will indicate the degree of right superduction. This
should be recorded accordingly. Conditions of this kind do not usually
exceed two or three degrees. The test, however, should be repeated
several times before the final result is recorded, as indicated in Fig.
24. The amount of superduction ranges from 1 to 4 prism diopters. The
normal average is 2.

[Illustration: Fig. 23—To test superduction, base down is required.
Rotary prism’s line or indicator should be rotated downward from zero.
To test subduction, base up is required. Indicator should be rotated
upward from zero.]

SUBDUCTION

Subduction, sometimes termed infraduction or deorsumduction, is the
relative power of the inferior recti to turn the eyes downward.
Prism power base up and apex down is employed. To test subduction,
the rotary prism should be operated with zero graduations placed
horizontally, as in the superduction test (Fig. 23), but the indicator
should be slowly rotated in the reverse direction, or upward from zero.
With the patient’s attention again directed to the large letter “E,”
or the Greek cross, the strongest degree prism thus secured without
diplopia will indicate the right subduction. The amount of subduction
ranges from 1 to 4 prism diopters. The normal average is 2.

Any difference between superduction and subduction, usually denoting
the existence of hyperphoria, should be given careful consideration.

PROCEDURE FOR MONOCULAR MUSCLE TESTING

As previously explained, after a duction test of each of the four
muscles of the right eye, the rotary prism before that eye should be
placed out of position and the procedure for adduction, abduction,
superduction and subduction repeated by means of the rotary prism
before the left eye. In case of an existing imbalance, after testing
the muscle of both right and left eyes, the refractionist can quickly
determine which muscle or muscles may be lacking in strength (Fig. 24).
In practically every instance muscle exercises or correcting prisms
may then be prescribed with definite knowledge of requirements, as
further described in the following paragraphs.

A binocular muscle test made with the phorometer, Maddox rod and
distant muscle-testing point of light might quickly indicate six
degrees of exophoria, both before and after the optical correction is
made. While this would doubtless be the correct amount of the manifest
imbalance, it would be a difficult matter to ascertain which muscles
caused the disturbance. To determine this important question, the
monocular or duction test should be invariably employed.

DIAGNOSING A SPECIFIC MUSCLE CASE

Assuming, for example, a specific case where six degrees of exophoria
was determined in the binocular test that the muscle findings in
the duction test show right adduction of twenty-four degrees, with
an accompanying abduction of eight degrees; likewise a superduction
and subduction of two degrees for each eye. With the aid of a chart
or diagram—which should be made in every case—a comparison of these
figures would indicate an exophoria of approximately six degrees, with
a corresponding weak left internus (Fig. 24). This not only shows the
muscle pull of each eye individually, but a comparison of the two eyes
as indicated by the dotted lines. Thus the relationship of the two
eyes, and their corresponding muscles is quickly indicated.

[Illustration: Fig. 24—Duction chart should be made in every case.
Above readily shows existence of muscular imbalance and proves
subduction and superduction for both eyes are equal; otherwise
hyperphoria would be disclosed. Also note abduction for both right and
left eye are equal, otherwise esophoria would be disclosed. Also note
adduction for right eye is 24° while left is but 18°, proving a case of
6° of exophoria with a left weak internus.]

A glance at the above diagram discloses the following three important
facts, all of which should be known to the refractionist before a
single thought can be devoted to the correcting of the case:

1. 6° exophoria is the amount of the insufficiency.

2. 18° adduction (which should be 24°).

3. Left weak internus.

As previously stated, the power to converge is normally rated 3 to 1,
or 8 to 24, as shown above, while the power of the eye to look upward,
is equal to the power to look downward. The diagram accordingly proves
that the muscles of the right eye are in perfect balance, having equal
muscular energy.

A comparison of the left eye shows adduction of 18 degrees with an
abduction of 8 degrees, proving a lateral insufficiency because the
ratio is less than 3 to 1; and the muscles of the left eye are at
fault. The power of 2 degrees superduction and 2 degrees subduction,
proves that no weakness exists in the vertical muscles.

After making the duction test for each eye individually, a comparison
of both eyes in relationship to each other may be more readily
determined by following the dotted lines (Fig. 24).

As previously stated, it is the inability of the two eyes to work
together that causes the imbalance, so that if both eyes were normal,
the adduction, abduction, superduction and subduction of the two eyes
would agree.

The duction chart (Fig. 24.) also shows that the corresponding muscles
of each eye agree—with the exception of the adduction of the right eye
and the left eye. This proves that the left internus is weak, measuring
only 18 degrees instead of 24 degrees; it further proves the 6 degrees
of exophoria in the monocular test, as was quickly and more readily
determined in the binocular test.

Likewise, in cases of esophoria, hyperphoria, or cataphoria, the making
of definite muscle measurements independently through the prescribed
method would show through the merest glance at a similar diagram which
muscle or muscles were relatively out of balance. Heterphoria of almost
any type, or tendencies other than normal, may be fully investigated by
making a thorough and separate test of each muscle.

Where an imbalance exists, a rapid test may be employed to distinguish
a pseudo or false condition from a true condition. This is accomplished
by first placing the two Maddox rods (both the red and white) so that
the rods lie in a vertical position. If the two lines fuse, we have
determined the existence of a false condition caused by a possible
error of refraction or nerve strain. If the lines separate, we have
determined a true muscular condition, and then only should the second
method of muscular treatment follow.

[Illustration: _Same as Model 215 but Automatic Cylinder Arrangement
omitted._

SKI-OPTOMETER MODEL 205

Embodying Spherical Lenses Combined with Appliances for Testing and
Correcting Muscular Imbalance.]

CHAPTER IX

FIRST METHOD OF TREATMENT OPTICAL CORRECTION

The mere determination of the degree of an imbalance, or even the
diagnosis of a patient’s trouble, is not sufficient. If relief is to be
secured, something more must be accomplished.

As previously stated, muscular imbalance may be corrected through
one of the four following rules or methods, each explained in their
relative order:

1—Optical Correction
2—Muscular Exercise
3—Use of Prism Lenses
4—Operative Methods

ESOPHORIA

To correct a case of muscular imbalance, where six degrees of esophoria
has been determined, the first rule of making the test for optical
correction with the Ski-optometer’s spherical and cylindrical lenses,
would be in the line of routine. The binocular test made with the
phorometer and combined use of the red Maddox rod would have determined
the six degrees of esophoria.

The reason for making the binocular muscle test before and after the
optical correction is because an imbalance is often aggravated or
benefited by the correcting lenses. The optical correction frequently
eliminates the need for further muscular treatment.

For example, we will assume that the optical correction tends to
decrease the degree of esophoria from six degrees to four degrees.
According to the previously mentioned rule for correcting cases
exceeding one degree in hyperphoria, three degrees in exophoria and
five degrees in esophoria, the condition would indicate that of being
“left alone.” Just what is taking place should be fully understood—its
cause as well as its effect.

[Illustration: Fig. 25—Comparative diagram showing how a decentered
lens before a centered eye has the same effect as a centered lens
before a decentered eye.]

When not otherwise specified, accurately centered lenses are of primary
importance. The pupil of the eye should be directly behind the center
of each lens (Fig. 25).

Figure “A” of the latter sketch illustrates a perfectly centered
lens—its center indicated by a cross, the circle representing an eye
directly behind it. Figure “B” illustrates a perfectly centered pupil
behind a prism, with its center designated by a cross. To ascertain
how the centered spherical lens takes the place of a prism, Figure “C”
should be compared with Figure “B”; this will show that the eye is
decentered, while the lens is centered. A further comparison will prove
that the results in Figures “B” and “C” are identical, the correcting
lenses having practically the same effect through the decentration
of the eye as if a prism were prescribed, nature supplying its own
decentration.

TREATMENT FOR CORRECTING ESOPHORIA IN CHILDREN

In case of esophoria, regardless of amount, slightly increased
spherical power is frequently prescribed for children. This will
naturally blur or fog the patient’s vision, but in their effort to
overcome the blur, accommodation is relaxed, usually tending to correct
the muscular defect.

In such cases, as a rule, a quarter diopter increased spherical
strength may frequently be added for each degree of esophoria as
determined before the optical correction was made. In a case of 6
degrees of esophoria, the refractionist may prescribe +1.50 diopter
spherical added to the optical correction, which, let us assume, is
+1.00 sph. = -1.00 cyl. ax. 180°, so that the treatment glasses would
be +2.50 sph. = -1.00 ax. 180° (See Procedure on Page 74).

At the end of each three months’ period, the patient should be
requested to return, when the binocular and the duction test should
again be made, comparing results with the work previously accomplished.
An improvement tending to build up the left weak externus will
possibly permit of a decrease of the excessive spherical power, so
that excessive spherical power is reduced until completely removed, in
all probability overcoming the muscular defect. Esophoria is almost
invariably a false condition and frequently is outgrown under this
treatment as the child advances in years. On the other hand, esophoria
uncared for in the child may tend to produce exophoria in the adult.

HOW OPTICAL CORRECTION TENDS TO DECREASE 6° ESOPHORIA IN A CHILD

[Illustration: Assume binocular muscle test made before optical
correction shows

6° Esophoria.

+1. Sph. = -1. Cyl. Ax. 180.]

Next, locate faulty muscle by making a duction test, which
shows how abduction of left eye is made to equal that of
right eye, change being made quarterly with treatment
lenses in accordance with following rule. Note as abduction
is increased, esophoria is reduced.

Rule—prescribe a quarter diopter increased sphere for each
degree of imbalance or 0.25 × 6 equals:

+1.50 added to optical correction.

1/1/19 (assumed date) prescribed treatment lenses equal:

+2.50 = -1. × 180°.

4/1/19 (3 months later) assuming abduction has increased from
2° to 3° showing difference of 5 Es. or 0.25 × 5. equals
+1.25 added to optical correction, prescribed treatment
lenses equal:

+2.25 = -1. × 180.

7/1/19 (3 months later), assuming abduction has increased
from 3° to 4° showing difference of 4° Es. or 0.25 × 4
equals +1.00 which added to optical correction would make
prescribed treatment lenses equal:

+2.00 = -1. × 180.

And so on, every three months treatment lenses are prescribed
until both right and left eye show 8° of abduction. In this
way the treatment lenses are reduced to original correction
of +1.00 = -100 × 180. This would have required six changes
of lenses, three months apart—thus consuming 18 months time.

CHAPTER X

SECOND METHOD OF TREATMENT—MUSCULAR EXERCISE

MADE WITH TWO ROTARY PRISMS AND RED MADDOX ROD

EXOPHORIA

If a case is one of exophoria of six degrees, where the second method
of treatment or muscular exercise is in line of routine, it is
essential to first determine through a duction test and the preparation
of the diagram exactly which one of the four muscles are faulty (Fig.
24).

Having determined, with the aid of the diagram, first, the existence of
6 degrees of exophoria; second, 18 degrees of adduction; third, a weak
left internus—the next procedure is to determine what degree of prism
will enable the patient to obtain single binocular vision, with both
eyes looking “straight.”

To determine this, place both of the Ski-optometer’s rotary prisms in
position with the handle of each pointing outward horizontally. The red
line or indicator of each prism should then be placed at 30° of the
outer scale (Fig. 26).

The red Maddox rod should be horizontally positioned before the eye,
the white line on indicator pointing to 180° of the scale (Fig.
27). The strength of the rotary prism before the right eye should
thereupon be reduced by rotating the prism indicator or red line toward
the upper zero (0) to a point where the patient first sees the red
streak—assuming that the red line appears at 42 degrees, that is 30
degrees before the left eye and 12 degrees before the right.

[Illustration: Fig. 26 (A and B)—First position of rotary prisms to
determine amount of prism exercise to be employed for building up the
weak muscle.]

The prism should then be still further reduced until the vertical
streak produced by the Maddox rod directly bisects the muscle testing
spot of light. Assuming that this point be thirty-eight degrees, which
is four degrees less, _single binocular vision is produced_.

[Illustration: Fig. 27—Position of red Maddox rod used in conjunction
with Fig. 26 for prism exercising.]

For example, sixty degrees of prism power (the combined power of the
two rotary prisms) will usually cause complete distortion. Therefore,
as outlined in Figure 28, the patient, seeing only out of the _right_
eye, will detect nothing but a white light. By gradually reducing the
strength of the prism before the right, which is the good eye, the
patient will eventually see a red streak off to the left. A continued
and gradual reduction to a point where the red streak bisects the white
light, will determine how much prism power is required for the patient
to obtain single binocular vision, thus establishing the same image at
the same time on each fovea or retina (Fig. 20).

This has taught the patient to do that which he has never before
accomplished. Therefore, after having been taught how to make the two
eyes work in relation to each other, the natural tendency thereafter
will be to strive for the same relationship of vision with both eyes.
The refractionist should then aim to reduce the excessive amount of
prism required to give binocular vision, which can be accomplished by
muscular exercise.

It must always be remembered before the refractionist is ready to
employ the muscular exercise or second method, that the degree of prism
required to give the patient single binocular vision must be determined
with the optical correction in place. The exercise must be practised
daily in routine, a daily record being essential.

AN ASSUMED CASE

We will assume a case where 42 degrees is required to enable the
patient to first see the red streak as produced by the Maddox rod to
the extreme left. Through a continued gradual reduction of 4 degrees
(or to 38 degrees), we next learn that the streak was carried over
until it bisected the white spot of light, giving single binocular
vision and producing a position of rest.

[Illustration: Fig. 28—Simplified chart showing the prism action
employed in developing a weak ocular muscle through alternating prism
exercise. Either side of 38° in excess of 4° causing diplopia.]

The patient has now established the limitation of the exercise, which
is four degrees, this limitation being determined by the difference
between the point where the streak was first seen to the extreme side
and where it bisected the spot. The same amount of four degrees should
then be used for the opposite side, thus reducing the prism strength to
34 degrees.

This again produces diplopia, because of the lesser amount of prism
power employed to give single binocular vision. The refractionist
should then return to 38 degrees, where single binocular vision had
originally been determined (Fig. 28), alternating back to 42, returning
to 38, over to 34, back to 38, and so on. This procedure should be
employed once a day just after meals for about five minutes, and
repeated ten times, constantly striving for a slight reduction of prism
power from day to day.

EFFECT OF MUSCULAR EXERCISE

This muscular treatment, or constructive exercising, should enable the
patient to overcome his amount of four degrees in either direction in
about a week. Hence in the case showing 38 degrees for single binocular
vision, results may be looked for in about nine weeks—four degrees
divided into 38 degrees. While the patient is undergoing the treatment,
which is nothing more than the strengthening of the interni muscles
or developing adduction, it is natural to believe that the amount of
imbalance is likewise being conquered. This, however, is readily
determined from time to time by making the binocular muscle test with
the phorometer and Maddox rod, as well as the duction chart test (Fig.
24), as previously outlined.

To fully appreciate the effect of this muscular treatment, the reader
need only hold his head in a stationary position, casting his eyes
several times from the extreme right to the extreme left, not failing
to note the apparent muscular strain. On the other hand, with the
aid of the Ski-optometer’s rotating prisms, the refractionist not
only has complete control of the patient’s muscles at all times, but
scientifically accomplishes muscular exercise without any tiresome
strain, overcoming all possible exertion.

After the case in question has been reduced to 30 degrees, having no
further use for the rotary prism, it may be removed from before the
right eye and the same exercising procedure continued as before with
the remaining left side rotary prism by reducing its power, until it is
likewise down to zero.

Having reduced both prisms to zero, each prism should again be placed
in position with zero graduations vertical and the prism indicator on
upper zero. Both prisms should then be turned simultaneously about
four degrees toward the nasal side of the patient, thus tending to
jointly force corresponding muscles of both eyes.

HOME TREATMENT FOR MUSCULAR EXERCISE—SQUARE PRISM SET USED IN
CONJUNCTION WITH THE SKI-OPTOMETER

Where a patient is unable to call each day for this muscular treatment
or exercise, the work will be greatly facilitated by employing a
specially designed set of square prisms ranging in strength from ½ to
20 degrees for home treatment. As in the case previously cited, it is
necessary to carefully instruct the patient that the interni muscles
_must_ be developed, hence prism base _out_ with apex in must be
employed. Attention should then be directed to a candle light, serving
as a muscle testing spot of light and stationed in a semi-dark room at
an approximate distance of twenty feet.

Having determined through the Ski-optometer the strength of the prism
required after each office treatment, its equivalent should then be
placed in a special square prism trial-frame which permits rotation of
the prism, although the patient is frequently taught to twirl the lens
before the eye. This exercise may be continued for about five minutes
each day.

The patient should also be instructed to call at the end of each week,
when the work may be checked by means of the Ski-optometer’s rotary
prisms, making the duction test as previously explained and outlined in
Fig. 24. It is then possible to determine whether or not satisfactory
results are being obtained. Otherwise the exercise should be abandoned.

Should the second method employed in the work of muscular imbalance not
prove effective, the third method requiring the use of prisms would be
next in routine.

CHAPTER XI

THIRD METHOD OF TREATMENT—PRISM LENSES

WHEN AND HOW EMPLOYED

As stated in the preceding chapter, on ascertaining the failure of the
second muscular treatment or method, prisms are employed for constant
wear. When prism lenses are used, whether the case is exophoria or
esophoria, or right or left hyperphoria, it is always safe to prescribe
one-quarter degree prism for each degree of prism imbalance for each
eye. For example, in a case of 6 degrees of esophoria, a prism of 1½
degree base out should be prescribed for each eye; or in 6 degrees
of exophoria, employ the same amount of prism, but base in. In right
hyperphoria, place the prism base down before the right eye and up
before the left, and vice versa for left hyperphoria.

It is not always advisable, however, to allow the patient to wear the
same degree of prism for any length of time. Many authorities suggest
a constant change with the idea that a prism is nothing more than a
crutch. Should the same degree be constantly worn, even though it
afforded temporary relief, the eye would become accustomed to it and
the purpose of the prism entirely lost. Prisms should be prescribed
with extreme care, their use being identical with that of dumb-bells,
where weight is first increased to maximum and subsequently reduced,
viz.:

PRISM REDUCTION METHOD

Where prisms are prescribed, it is considered good practice to make a
binocular muscle test and the duction test (Fig. 24) at the end of each
three months’ period, employing the phorometer, Maddox rod, and rotary
prisms, as already explained.

If the condition shows any decrease, the prism degree should be
proportionately decreased. For example, in the case originally showing
6 degrees of exophoria, one-quarter degree prism for each degree of
imbalance was prescribed, or 1½ degree for each eye. If the same case
subsequently indicated 4 degrees, only one degree for each eye should
be prescribed—and so on, a gradual reduction of prism value being
constantly sought.

Except in rare cases, prisms should not be prescribed with the base
or apex at oblique angles, as the eye is rarely at rest with such a
correction. An imbalance may be caused by a false condition in one
rectus and a true imbalance in the other, giving one the impression
that cyclophoria exists, as explained in a following chapter.

Having now employed the three methods, the refractionist can readily
understand that a marked percentage of muscular imbalance cases may be
directly benefited through the aid of the Ski-optometer. If these three
methods of procedure fail, there is nothing left but the fourth and
last method—that of operative procedure.

CHAPTER XII

A CONDENSATION OF PREVIOUS CHAPTERS ON THE PROCEDURE FOR MUSCLE TESTING
WITH THE SKI-OPTOMETER

The present chapter, intended for those desiring a synopsis or
condensed summary of muscular imbalance work, should prove of the
utmost assistance to the busy refractionist. Muscular imbalance work
can be successfully conducted if the following routine is studied and
memorized, with the Ski-optometer _constantly before the reader_.
The chapters containing the corresponding figures and diagrams or
illustrations will then be readily comprehended. It is also important
to carefully note the captions under each diagram.

1. Without any testing lenses before patient’s eyes, direct attention
to a 20-foot distant muscle testing spot of light (Fig. 9).

2. Place phorometer handle vertically (Fig. 16).

Place red Maddox rod vertically (Fig. 15). Patient should see a white
spot of light, and a red horizontal streak (Fig. 17).

Simply turn phorometer handle until horizontal streak bisects white
spot of light. Pointer then indicates amount of deviation on red
scale. Ignore cases less than 1° hyperphoria, whether right or left
designated by (R. H.—L. H.).

3. Place phorometer handle horizontally (Fig. 19).

Place red Maddox rod horizontally (Fig. 18). Patient should see a white
spot of light and a vertical red streak (Fig. 20).

Simply turn phorometer handle until red streak bisects spot of light.
Pointer indicates amount of deviation on white scale, whether esophoria
or exophoria designated by (Es—Ex).

4. Ignore all exophoria cases, less than 3°.

Ignore all esophoria cases, less than 5°—except in children, ignore
less than 3° of esophoria.

5. Always make the above or binocular muscle test—with phorometer
and red Maddox before optical correction or (test for spheres and
cylinders) and again after optical correction where case shows more
than 1-3-5 rule, to determine whether muscles are aggravated or
benefited.

6. In cases showing more than the 1-3-5 rule, shown in above No. 4,
make monocular duction test first with rotary prism before patient’s
right eye,—then with rotary prism before left eye to find faulty muscle
and determine which eye is affected.

7. To test adduction, prism base out is required. Rotary prism’s red
line or indicator should be rotated from zero outwardly. To test
abduction, base in is required. Indicator should be rotated inwardly
from zero (Fig. 22). Power of adduction as compared with abduction, is
normally 3 to 1—usually rated 24 to 8.

8. To test superduction, base down is required. Rotary prism’s line or
indicator should be rotated downward from zero. To test subduction,
base up is required. Indicator should be rotated upward from zero.
Power of superduction as compared with subduction, is normally
equal—usually rated 2 for each (Fig. 23).

9. Direct patient’s attention to largest letter on distant chart,
usually letter “E,” rotating red line indicator of rotary prism
outlined in above No. 7 and No. 8, until diplopia is first procured.

10. The use of a duction chart on a record card, quickly designates
pull for each of four muscles (Fig. 24), illustrating an assumed case
of—

1st—6D of Exophoria.
2nd—18° adduction (which must be developed to 24°).
3rd—Patient has a left weak internus.

11. Employ First Method—Optical Correction—to effect treatment.

12. Assuming a case of a child with 6° of esophoria—8° of right
abduction and 2° left abduction indicating a left weak externus,
prescribe a quarter diopter increased plus spherical power for
each degree of imbalance, thus adding +1.50D spherical to optical
correction. This is the _first_ method of treatment. This requires a
thorough reading of Chapter IX on Treatment for Correcting Esophoria in
Children and a careful study of the formula. For synopsis see Page 74.

FOUR METHODS OF TREATING AN IMBALANCE CASE WHEN THE PRECEDING ONE FAILS

1st—Optical correction;

2nd—Muscular exercise or treatment;

75% ARE CURABLE WITH FIRST AND SECOND METHODS.

3rd—Prisms;

5% ARE CURABLE WITH THIRD METHOD.

4th—Operation;

20% ARE CURABLE WITH FOURTH METHOD.

13. When first method of treatment fails, EMPLOY SECOND METHOD—Muscular
Exercise—to effect treatment.

1st—Find degree of prism patient will accept to produce single
binocular vision with optical correction on, placing both rotary prisms
in position, handles horizontal, red line on 30° of temporal scale of
each, giving total value to 60° (Fig. 26a and b).

2nd—Also place red Maddox rod before patient’s eye (rods horizontal)
(Fig. 18), calling patient’s attention to usual muscle testing spot of
light.

3rd—Reduce prism before good eye until red streak appears, noting
degree (which we assume shows 42° the combined total value of both
prisms) slowly continue to decrease prism until streak bisects spot.
Assume this shows total of 38°. Either side of 38° in excess of 4° (38
to 42) produces diplopia. Prisms must only be rotated from 38° to 42°
back to 38° over to 34°—back to 38° over to 42°—back again to 38° and
so on—exercise to be continued daily ten times for five minutes (Fig.
28).

4th—At end of each week, duction test should again be made. Duction
chart should show a tendency to reduce exophoria by a gradual building
up of adduction, approximately one week is usually sufficient to teach
patient to hold streak within the spot (between 38° and 42°). Exercise
to be continued until both prisms are worked down to zero. Exercise
tends to teach patient how to establish same image on each fovea or
retina at same time.

5th—If patient is unable to call daily for treatment, employ home
treatment. (Read “Home Treatment for Muscular Exercising,” Page 82).

Employ THIRD METHOD—Use of Prisms for Constant Wear to effect treatment.

PRISMS

1st. Where a case cannot be reduced through use of first two methods,
as for example in a case of 6° of exophoria, prescribe ¼ of amount of
imbalance (¼ × 6 = 1½°) for each eye—base in—or esophoria base out,
hyperphoria base up on eye affected.

2nd. Advise patient to call every three months and make duction test
(Fig. 24). If no improvement in condition, after wearing prisms six
months, operative means is suggested.

Assume a case is benefited, reduce prism power according to rule; ¼D
prism for each degree of imbalance.

CYCLOPHORIA

This work being of a technical nature, it is deemed best for the reader
to study Chapter XIII and XIV.

CHAPTER XIII

CYCLOPHORIA

MADE WITH MADDOX RODS AND ROTARY PRISMS

Cyclophoria, a condition affecting the oblique muscles of the eye, is
caused by its rotation. It is detected in the following manner by the
combined use of the red and white Maddox rods and the rotary prism.

[Illustration: Fig. 29—Position of rotary prism for producing diplopia
in testing cyclophoria with prism placed at 8° base up.]

Darken the room and direct the patient’s attention to the usual
muscle-testing spot of light, located approximately twenty feet away
and on a direct plane with the patient’s eye. The optical correction,
if one is required, should always be left in place—just as in making
other previously described muscle tests.

The rotary prism should then be brought before the patient’s right eye
with the handle-pointing upward and with zero graduations horizontal.
The indicator or red line should then be rotated upward from zero to
eight upon the prism scale, creating the equivalent of a prism of
8 diopters with base up (Fig. 29). This normally caused diplopia,
although in some cases it may be necessary to place the prism at 10 or
12 degrees before diplopia is produced.

[Illustration: Fig. 30—(A. and B.)—First position of both Maddox rods
used in conjunction with Fig. 29 for determining cyclophoria.]

The red Maddox rod should then be brought into operative position
before the patient’s left eye (Fig. 30a) and the white Maddox rod
before the patient’s right eye, (Fig. 30b) setting each one so that
the rods lie in a vertical position with their white line on the large
red zero (0).

The patient should now see two separate and distinct streaks of light,
one appearing below the other.

[Illustration: _DETERMINING CYCLOPHORIA_

_RIGHT EYE_ _LEFT EYE_

_Fig. 31_ _Fig. 34_

_NO CYCLOPHORIA_ _NO CYCLOPHORIA_]

[Illustration: _Fig. 32_ _Fig. 35_

_+ CYCLOPHORIA_ _+ CYCLOPHORIA_]

[Illustration: _Fig. 33_ _Fig. 36_

_- CYCLOPHORIA_ _- CYCLOPHORIA_

Figs. 31-36—Diagram showing how streaks appear to patient, as produced
by the Maddox rods in testing for cyclophoria.]

Should there be no cyclophoria of the right eye, the streaks will
appear in a horizontal plane parallel to each other (Fig. 31).

Should the red streak appear horizontally to the left eye, and the
white streak seen by the right eye appear at an angle therewith,
cyclophoria of the right eye would be indicated (Fig. 32).

In brief, should the white streak dip towards the patient’s left side,
the case would be one of right _plus_ cyclophoria (Fig. 32); whereas
right _minus_ cyclophoria would be indicated should the white streak
dip to the patient’s _right_ side (Fig. 33).

Next, setting the rotary prism of 8 degrees, placed base up before the
patient’s left eye, the _red_ streak should appear below the _white_
one. Should the two streaks appear horizontally, parallel with each
other, there would be _no_ cyclophoria of the left eye (Fig. 34).

If, however, the upper or white streak should appear horizontal, and
the lower or red streak at an angle therewith dipping toward the
patient’s _right_ side, the left eye would be cyclophoric and the case
would be one of left _plus_ cyclophoria, as the chart indicates (Fig.
35).

Should the red streak dip in toward the patient’s _left_ side, left
_minus_ cyclophoria would be designated (Fig. 36).

The patient would instinctively describe, with pointed finger and hand
motion, the position of the “dipping” line just as one would describe a
spiral staircase. Should this test determine that no cyclophoria exists
in either eye, there would be no necessity for further tests.

Some authorities claim that both Maddox rods should be of the same
color, so as to more readily assist the patient to fuse the two
objects. If the reader so desires, he can readily place a red lens from
the trial-case in the forward cell of the instrument.

The characters _plus_ and _minus_ in cyclophoria merely refer to _plus_
as signifying a tendency toward the _temporal_ side; _minus_ indicating
a tendency toward the _nasal_ side. This has no bearing on “convex” and
“concave,” which are frequently designated as “plus” and “minus.”

The test for cyclophoria is particularly essential, proving of utmost
importance where the patient requires an astigmatic correction with the
cylinder axis in oblique meridian. The case should then be investigated
in every instance by making a thorough and separate test of each eye
for cyclophoria.

In a case where cyclophoria is determined, the trouble may be caused by
the functioning of _other_ muscles, through the drain of nerve force,
thus disturbing the harmony of _every_ muscle action.

Cyclophoria is frequently caused by an imbalance of two recti, giving
an oblique pull. In most cases, it is merely necessary to release the
torsion, as described in the following chapter.

CHAPTER XIV

CYCLODUCTION TEST

MADE WITH THE COMBINED USE OF THE TWO MADDOX RODS

Having determined that cyclophoria exists, as previously outlined,
the next step would be to make a cycloduction test, or a test of the
oblique muscles individually. Maddox rods, both red and white, should
be placed in position with the rods horizontal—the plus and minus sign
at 90 degrees on the scale (Fig. 37). The patient’s attention should
be directed to the usual muscle-testing spot of light, when a vertical
band of light will appear to the patient, as shown in Fig. 38.

[Illustration: Fig. 37—(A. and B.)—Primary position of combined use of
both Maddox rods for determining cycloduction test.]

[Illustration: _FIG. 38_

_NORMAL_]

[Illustration: _FIG. 39_

_RIGHT +CYCLODUCTION_

_LEFT -CYCLODUCTION_]

[Illustration: _FIG. 40_

_RIGHT -CYCLODUCTION_

_LEFT +CYCLODUCTION_

Figs. 38-40—Diagram showing position of streaks produced by Maddox rods
as they appear to patients in making cycloduction tests.]

To measure the duction range of the inferior oblique of the right eye,
it is merely necessary to slowly rotate the Maddox rod before the right
eye upward at its nasal end to the point where the band of light breaks
so as to resemble a letter “X”. This gives in degrees the amount of
right plus cycloduction, as indicated on the temporal scale, when it
will appear to the patient, as shown in Fig. 39.

The Maddox rod should then be restored to its original position, with
the plus and minus on the 90 degree line of the scale (Fig. 37), and
rotated upward at the temporal end until it again takes the form of the
letter “X”. (Fig. 40.) The position of the indicator will now denote
the amount of right minus cycloduction, or duction range of the right
superior oblique muscles. Having determined the duction range of the
oblique muscles of the patient’s right eye, both Maddox rods should be
placed in original position with rods horizontal and plus and minus
sign on 90° of scale, as shown in Fig. 37.

The Maddox rod before the left eye is then employed exactly in the
same manner as before when the test for the right eye was made. A plus
cycloduction of the left eye would be indicated, as shown in Fig. 40,
while a minus cycloduction of the left eye would appear to the patient,
as shown in Fig. 39.

By recording a comparison of each eye, as explained, it will be found
that the range of duction usually averages five to twenty degrees
on either side of the 90 degree line, as indicated on the scale
surrounding the Maddox rods.

It will be recalled that cyclophoria was only to be looked for in
oblique astigmatic cases. It is frequently possible to correct the
patient’s trouble, by changing the axis of the cylinder, before one or
both eyes, a minus cycloduction signifying a change of axis towards
180° while a plus toward 90°, according to the amount lacking in full
duction power. It is also well to exercise the oblique muscles through
a rotation of the Maddox rod before the affected eye, whether it be
one or both that is lacking in full duction power, until the required
amount is reached to equal its fellow member.

For a more exhaustive treatise the author suggests a reading of Dr.
Savage’s work on the subject.

TREATMENT FOR CYCLOPHORIA

As previously stated, it often proves of great benefit to employ a
muscular exercise where a patient has an existing cyclophoria of either
one or both eyes, results derivable through the exercise of the recti
muscles having been previously detailed.

To exercise the oblique muscles of the right eye, _both_ Maddox
rods should be placed in the original position employed for making
cycloduction test, as previously explained (Fig. 37). This causes the
patient to see but _one_ band or vertical streak (Fig. 38).

The Maddox rod, placed before the right eye, should be slowly rotated
inward from ninety degrees to a point on the scale where the single
streak of light breaks, when it should again be returned to ninety
degrees. This causes a contraction and relaxation of the muscles in
the form of an exercise and should be repeated ten times—about five
minutes each day. By employing the Maddox rod before the left eye in
precisely the same manner, its oblique muscles will be exercised.

To determine whether or not this form of exercise is beneficial to the
patient, the weekly cycloduction test, as previously described, should
be made and compared with the original findings.

[Illustration: _A Compact Phorometer and Trial-Frame._

SKI-OPTOMETER MODEL 235

For Testing and Correcting Muscular Imbalance—Providing a Comfortable
Form of Trial-Frame.]

CHAPTER XV

MOVEMENTS OF THE EYEBALLS AND THEIR ANOMALIES

After a careful study of the foregoing chapters, the refractionist may
desire _further_ knowledge concerning muscular imbalance—a matter in
which the Ski-optometer plays an exceptionally important part.

It should be remembered that it is only the general utility of the
instrument, _plus_ one’s knowledge of refraction and individual
diagnosis that enables the refractionist to attain maximum efficiency
in every examination, a fact which largely accounts for the following
chapter.

MONOCULAR FIXATION

When we view an object _directly_, so that it appears to be more
distinct than surrounding objects, we are said to “fix” or “fixate” it.

As the fovea is normally the most sensitive part of the retina,
affording by far the most distinct vision, “fixation,” in the great
majority of cases, is so performed that the image of the object that
is “fixated” falls upon the fovea of the eye that is “fixing.” This is
known as central or muscular “fixation.”

When central vision is absent, however, the patient is compelled to
see with a portion of the retina _outside_ of the fovea. The eye must
then be so directed as to cause the image of the object to fall on this
outlying portion of the retina. This is termed “eccentric fixation,”
and usually denotes that vision is exceptionally poor.

The ability to “fix” is apparently acquired in early infancy by
constant practice in looking at objects. Any marked interference with
vision, particularly with central vision—present at birth or soon
thereafter—will tend to prevent the acquisition of this ability, and in
_extreme_ cases the eye does not learn to “fix” at all, but aimlessly
wanders in all directions.

BINOCULAR FIXATION

We habitually use the eyes together, fixating with both at once; that
is, we direct the eyes in such a way that the image of the object to
which the attention is directed falls on the fovea of each eye.

Where both eyes are accurately directed to an object at which one or
both are looking, the condition is known as “binocular fixation,” which
is commonly understood to mean that _both eyes are straight_.

The ability to produce and maintain binocular fixation—to keep both
eyes directly straight—is acquired early in life. The impulse to
maintain it grows with exercise, and soon becomes so strong that after
the age of infancy binocular fixation is present in the great majority
of persons, and in most of them is present all the time.

Binocular fixation must be distinguished through three
conditions—_orthophoria_, _heterophoria_ and _squint_.

ORTHOPHORIA

This is the condition in which both eyes look straight at the same
object, whether both see it or not. There is not the slightest tendency
of deviation.

HETEROPHORIA

This is the condition in which both eyes keep looking straight at
the same object so long as both _see_ it; but as soon as one eye
is excluded from vision (as by a screen) that eye deviates. This
is then a tendency of deviation which is strong enough to become
manifest when either eye is covered, but which is abolished or
overcome by the compelling impulse of binocular fixation as soon as
both eyes are used for seeing. A heterophoria thus produces a maximum
deviation. The deviation is also said to be _latent_, since it is
absent under ordinary conditions and is brought to light only under
special conditions. A common though improper term for heterophoria is
“insufficiency.”

SQUINT

Squint is the condition in which there is so great a tendency to
deviation that even when both eyes are uncovered, one deviates and
only one “fixes.” It differs, therefore, from heterophoria in that the
deviation it produces is obvious under ordinary conditions.

Squint is also called strabismus, or heterotropia. In other words, in
orthophoria there is binocular fixation _all the time_ and under all
conditions; in heterophoria it is present only when the two eyes are
uncovered, so that both see the object looked at; while in squint it is
not present at all.

Or, in still plainer terms, in orthophoria both eyes are straight
all the time; in heterophoria both are straight, but only so long as
both are uncovered; and in squint only one eye is straight, no matter
whether both eyes are uncovered or not.

In squint, while binocular fixation is altogether absent, the ability
to perform monocular fixation is almost always preserved; i.e., the
squinting eye will “fix” at once if the other eye is covered. It is
only when there is marked amblyopia, particularly as the result of a
central scotoma (or spot on the cornea in the line of vision) that the
squinting eye loses its power to fix at all, and wanders uncertainly
about, receiving impressions now on one, now on another portion of the
retina.

The term imbalance is often used to denote the two conditions opposed
to orthophoria; i.e., to denote collectively heterophoria and squint.

VARIETIES OF HETEROPHORIA AND SQUINT

1. _Classification According to Direction of Deviating Eye_:
Heterophoria and squint may be classified according to the direction
assumed by the deviating eye. Thus we have the following varieties of
heterophoria:

HETEROPHORIA
LATERAL DEVIATIONS

Either eye deviates
In, or toward the nose Esophoria
Out, or toward the temple Exophoria

VERTICAL DEVIATIONS
The right eye goes up and the left down Right Hyperphoria
The left eye goes up and the right down Left Hyperphoria

In rare cases of vertical heterophoria, each eye has either an upward
tendency (anophoria) or a downward tendency (cataphoria). These cases
must not be confused with anatropia and catatropia. In anaphoria and
cataphoria, there is binocular fixation when both eyes are uncovered,
while in anatropia and catatropia _one_ of the eyes squints. This shows
the following squint condition:

SQUINT

LATERAL SQUINT
The deviating eye turns in, or toward the nose:
Esotropia (Strabismus convergens—Convergent Squint)

The deviating eye turns out or toward the temple:
Exotropia (Strabismus divergens—Divergent Squint)

VERTICAL SQUINT
The deviating eye turns up:
Hypertropia (Strabismus sursumvergens) (Right or left)

The deviating eye turns down:
Hypotropia (Strabismus deorsumvergens) (Right or left)

In addition to these lateral and vertical deviations, conditions exist
in which the vertical meridian of one eye, instead of maintaining its
parallelism with the vertical meridian of the other, either forms (or
tends to form) an angle with it (cyclotropia), but is kept in position
through muscular effort (cyclophoria.)

Cyclotropia is usually due to paralysis of one of the ocular muscles,
causing the vertical meridian of the affected eye to be tilted out
or toward the temple (extorsion) or in toward the nose (intorsion).
A tilting of the vertical meridian toward the right is also called
dextrotorsion (or positive declination); and to the left, levotorsion
or negative declination.

2. _Constant, Intermittent and Periodic Deviations_: A deviation,
whether squint or heterophoria, may be present at all times (constant),
or occasionally present and occasionally absent (intermittent). In
this case we may have heterophoria alternating with orthophoria, or
heterophoria alternating with squint; or squint alternating with
orthophoria. We also find variations such as a squint for near and
a heterophoria or orthophoria for distance; or a heterophoria for
near and orthophoria for distance; or a constant squint for near and
an intermittent squint for distance, etc. Again, a deviation may be
periodic, in that its amount for distance may greatly exceed that for
near, or vice versa.

Opposed to a periodic deviation is one which is present, and in about
equal amount, both for distance and near. Such a deviation, whether
squint or heterophoria, is called “continuous.”

3. _Alternating and Uniocular Squint_: An alternating squint is one
in which when both eyes are uncovered, so that both have a chance to
“fix”; sometimes the right eye will deviate, sometimes the left. In
uniocular (less properly monocular) squint, under the same conditions,
one eye, either the right or the left, always “fixes” and the other
always deviates. A uniocular squint is denoted as right or left,
according to whether it is the right or left eye which deviates.

[Illustration: A TYPICAL REFRACTION ROOM—THE WOOLF SANITARY ALL-METAL
EQUIPMENT

Installation comprising: Ophthalmic Chair, complete with Ski-optometer,
Test Letter Cabinet, Asceptic Trial-Case Cabinet, Muscle Testing
and Skioscopic Lamp, Ophthalmometer, Perimeter, Adjustable Tables,
Adjustable Stool.]

4. _Comitant and Non-Comitant Deviations_: In some varieties of
heterophoria and squint, the amount of deviation is the same in all
directions of the gaze, so that the angle between the visual line of
one eye and that of the other remains the same, no matter which way the
eyes are turned. Such deviations are called comitant or non-comitant,
because one eye accompanies and keeps pace with the other in all its
movements. In other cases, the deviation changes as the eyes are moved
in different directions, so that the angle between the two visual lines
constantly varies. Such deviations are termed concomitant. Usually in a
non-comitant squint the angle of deviation increases in a regular way
as the eyes are moved in one direction and decreases as they move in
the direction opposite.

In cases of long standing, however, the squinting eye, particularly
when very amblyopic, wanders in an uncertain way and apparently quite
without reference to the movements of the other eye.

CHAPTER XVI

LAW OF PROJECTION

The movements of the eye are designed primarily to effect fixation—that
is, to bring upon the macula the image of the object that we wish to
look at. When this has been accomplished, we know as a result of long
experience, the direction of the object looked at and also direction of
other neighboring objects. This knowledge is doubtless afforded us, in
part, by our muscle sense. Thus we know that an object, A, is straight
in front of us because we can see it sharply without moving either the
head or the eyes from the position of rest or equilibrium; and we know
that an object, B, is on the right of us because to see it sharply we
have to move either the head or the eyes to the right, thus altering
the muscular condition from one of rest to one of tension. But without
moving either head or eye, we also know, while still looking at A, that
B is to the right, for the image of B is then formed on a portion of
the retina situated to the left of the macula. From long experience
we also know that an image so situated means an object placed on our
right. Moreover, the farther to the left of the macula the image B is,
the farther to the right do we judge B itself to be.

Similarly, if B is so placed that its image falls below the macula,
we then know B itself is really above A, which forms its image on the
macula; and if the image of B is above the macula, we know that B
itself is below A.

The table on page 116 is suggested as a guide in cases of muscular
imbalance:

SUPPRESSION OF IMAGE

All deviations should be and probably are primarily associated with
diplopia. Yet in the great majority of cases of established squint,
especially convergent squint, there is no double vision. This is due to
the mental suppression of the image by the squinting eye. In such cases
all attempts to evoke diplopia by our tests may be futile, the patient
not appreciating the presence of double images even when they are
widely separated by prisms. Moreover, this suppression usually persists
after the squint is cured, so that even though there are two retinal
images of the same object, the mind perceives but _one_ and ignores the
_other_, just as though it were not present. In this case there is no
true stereoscopic, or solid, vision.

MONOCULAR DIPLOPIA

Binocular diplopia, due to deviation of the eyes or to prisms, must
be distinguished from monocular diplopia, or the condition in which
the patient sees double with one eye alone. This occurs as the result
of astigmatism, plus spherical aberration and other conditions found
occasionally in squint. It can readily be differentiated by the fact
that binocular diplopia disappears when the patient shuts either eye;
while monocular diplopia, of course, does not.

TABLE OF DIPLOPIA

==================+===========+=====================================+
| Image of | |
| right eye | CAUSED BY |
|as compared+-------------------+-----------------+
Name of |with that | |(2) Artificially |
diplopia | of the | (1) By a natural | by a prism |
| left is | deviation of | placed, base |
------------------+-----------+-------------------+-----------------+
{Homonymous | On the |Either eye inward |In before either |
{ | right | (esophoria, | eye. |
Lat-{ | | esotropia.) | |
eral{ | | | |
{Heteronymous| On the |Either eye outward |Out before either|
{(or crossed)| left | (exophoria, | eye. |
| | exotropia.) | |
------------------+-----------+-------------------+-----------------+
{Right | Below |Right eye up |Up before right |
{ | | or left eye down | eye, down before|
Vert-{ | |(right hyperphoria,| left eye. |
ical{ | | right hypertropia,| |
{ | | left hypotropia.) | |
{ | | | |
{Left | Above |Right eye down |Down before right|
| | or left up |eye, up before |
| |(left hyperphoria, | left |
| | left hypertropia, | |
| | right hypotropia.)| |
==================+===========+===================+=================+
| Image of | |
| right eye | CORRECTED BY |
|as compared+-------------------+-----------------+
Name of |with that | | |
diplopia | of the | (1) Turning |(2) Prism placed |
| left is | | with base |
------------------+-----------+-------------------+-----------------+
{Homonymous | On the |Both eyes outward |Out before either|
{ | right | (divergence.) | eye. |
Lat-{ | | | |
eral{Heteronymous| On the |Both eyes inward |In before either |
{(or crossed)| left | (convergence.) | eye. |
| | | |
------------------+-----------+-------------------+-----------------+
{Right | Below |Right eye down |Down before right|
Vert-{ | | and left eye up | eye or up before|
ical{ | | (left | left eye. |
{ | | supravergence.) | |
{ | | | |
{Left | Above |Right eye up and |Up before right |
| | left eye down | eye or down |
| | (right | before left. |
| | supravergence.) | |
==================+===========+===================+=================+

MOVEMENT OF EACH EYE SINGLY

The movements of each eye individually are effected as follows:

The external rectus moves the eye directly outward; the internal
rectus, directly inward.

The primary action of the superior rectus is to raise the eye. Because
of the way in which the muscles run, obliquely from within outward, its
lifting action increases when the eye is abducted and diminishes to
little or nothing when the eye is adducted.

The inferior rectus carries the eye down. Owing to the oblique
direction of the muscle, its depressing action increases as the eye is
abducted and decreases to zero as the eye is adducted.

The inferior oblique is inserted back of the equator of the eye. Hence
it pulls the back part of the eye down and consequently throws the
front part up. It is thus an elevator of the eye, reinforcing the
action of the superior rectus. Owing to the way in which it runs, from
the front backward and outward, its elevating action is greatest when
the eye is adducted, and diminishes to little or nothing when the eye
is abducted.

The superior oblique, so far as its action on the eyeball is concerned,
may be regarded as arising from the trochlea. From this point it runs
backward and outward and is inserted back of the equator of the eye.
It there pulls up the back part of the eye and consequently throws the
front part down. It is thus a depressor, reinforcing the action of
the inferior rectus. Owing to the oblique way in which it runs, its
depressing action is greatest when the eye is adducted, and diminishes
to little or nothing when the eye is abducted.

SUBSIDIARY ACTIONS

Besides these actions, rightly regarded as the main action of the
ocular muscles, there are various subsidiary actions, due to the
oblique way in which the superior and inferior recti and the two
obliques run. Thus, both the superior and inferior recti adduct the
eye, their action being most pronounced when the eye is already
adducted. The two obliques, on the other hand, abduct the eye and do so
most effectively when the eye is already abducted.

The superior rectus and superior oblique rotate the top of the vertical
meridian of the eye inward (intorsion); while the inferior oblique
and inferior rectus rotate it outward (extorsion). The superior and
inferior recti act thus on the vertical meridian mainly when the eye is
adducted; the oblique, on the other hand, when the eye is abducted.

Hence the eye is adducted by the internal rectus, assisted toward the
end of its course by the superior and inferior recti. It is abducted by
the external rectus, assisted toward the end of its course by the two
obliques. It is carried straight up by the superior rectus and inferior
oblique, up and out by the superior rectus and external rectus (the
inferior oblique helping to carry it out, but not up; and in, mainly by
the inferior oblique and internal rectus). The superior rectus assists
in carrying it in, but hardly up at all.

The eye is likewise carried straight down by the inferior rectus and
the superior oblique; down and out by the inferior and external recti,
and down and in by the superior oblique and internal recti.

FIELD OF ACTION OF MUSCLES

As will be seen, each muscle acts most energetically in some special
direction of the gaze, termed field of action of that particular
muscle; thus the external rectus acts most powerfully when the eye
is directed outward, and acts little or not at all when the eye is
directed inward, except by purely passive traction. Likewise the
superior rectus acts mainly when the eye is directed down. Furthermore,
its action is limited to the upper and outer field; for in the upper
and inner field elevation is performed chiefly by the inferior oblique.

This is also true of all the other muscles.

DIRECTION OF THE GAZE

There are six cardinal directions of the gaze, each corresponding to
the field of action of one of the six ocular muscles as follows:

CARDINAL DIRECTION: MUSCLES SPECIALLY ACTIVE:

Straight out External rectus
Straight in Internal rectus
Up and out Superior rectus (as an elevator)
Up and in Inferior oblique (as an elevator)
Down and out Inferior rectus (as a depressor)
Down and in Superior oblique (as a depressor)

It is to be noted that the action of each muscle does not absolutely
_stop_ at the middle line, but extends somewhat beyond it. Thus the
action of the right externus extends not only throughout the whole
right half of the field of vision, but also some fifteen to twenty
degrees to the left of the median line; and that of the superior rectus
extends not only above the horizontal plane but also somewhat below.

PRIMARY POSITION—FIELD OF FIXATION

Under normal conditions, when the head is erect and the eye is directed
straight forward—that is, when its line of sight is perpendicular
to the line joining the centres of rotation of the two eyes in the
horizontal plane—the muscles are all balanced. This is called “the
position of equilibrium” or the primary position. It is this position
which must be assumed by the patient in conducting tests for balance of
the muscles.

From the primary position, the eye may make excursions in every
direction so that the patient can look at a whole series of objects in
succession without moving the head. This portion of space, occupied
by all the objects that may thus be seen directly by moving the eye
without moving the head, is called “the field of fixation.”

BINOCULAR MOVEMENTS

While either eye alone may move in all possible directions, one cannot
move _independently_ of the other eye. Under ordinary circumstances,
those movements only are possible which are regularly required to
subserve binocular vision, hence, binocular single vision, as well.
These movements are as follows:

PARALLEL MOVEMENTS

When one eye looks at a distant object the other is also directed to
it, so that the lines of sight of the two eyes are parallel; if the
distant object is moved about, the lines remain parallel, one moving as
fast and as far as the other. These parallel movements of the two eyes
are executed with considerable freedom in all directions, either eye
being able to move readily to the right, left, up, down, or obliquely,
provided the other eye moves precisely with it.

In executing any parallel movement, each eye is acted upon by at least
three and sometimes by as many as five muscles. At times, but one of
these muscles is required to produce any _great_ movement of the eye,
the others simply serving to steady it in its course. Thus when we look
up to the right, although there are five muscles really acting upon
each eye, the right eye is moved mainly by the _external_ rectus and
the left eye by the _internal_ rectus.

Similarly, when we look up and to the right, although other muscles
take part, the superior rectus is the chief muscle that moves the
right eye up, and the external rectus the chief one that moves it to
the right; while for the left eye the inferior oblique and the internal
rectus are the efficient muscles.

A careful study of the action of the individual muscles will make it
clear that these facts hold good for each of the cardinal directions of
the gaze.

Furthermore, if we attentively consider the action of the twelve
muscles moving the two eyes, we see that they may be divided into three
groups, _viz._; four _lateral rotators_, four _elevators_ and four
_depressors_.

LATERAL ROTATORS
Right rotators } { Left rotators
L. Internal rectus } to { R. Internal rectus
R. External rectus } { L. External rectus

ELEVATORS
Right-handed elevators } { Left-handed elevators
(acting mainly when the } { (acting mainly when the
eyes are directed to the } to { eyes are directed to the
right) } { left)
R. Superior rectus } { R. Inferior oblique
L. Inferior oblique } { L. Superior rectus

DEPRESSORS
Right-handed depressors } { Left-handed depressors
(acting mainly when the } { (acting mainly when the
eyes are directed to the } { eyes are directed to the
right) } to { left)
R. Inferior oblique } { R. Superior oblique
L. Superior oblique } { L. Inferior rectus.

Each group, it will be seen, comprises _two_ pairs of muscles; one
pair acting solely when the eyes are directed to the right, the other
when they are directed to the left. It will further be noted that of
the two muscles constituting any one pair, one is situated in the right
eye, the other in the left.

EYE ASSOCIATES

The muscles forming any one pair are called associates. Any two
associates acting together will move their respective eyes in precisely
the same direction and to the same extent. Thus the right superior
rectus moves the eye up to the left and rotates its vertical meridian
to the left; and its associate, the left inferior oblique, moves its
eye up to the left and rotates its vertical meridian to the left. This
likewise applies to each of the other five groups of associates.

If one eye fails to keep pace with the other in executing parallel
movements, diplopia ensues. If the eyes are moved in all directions
and the point noted where the patient just begins to see double, we
_delimit_ the field of binocular single vision.

Normally, however, the two eyes maintain parallelism to the very
limit of their excursion, so that diplopia occurs only at the extreme
periphery of the field of vision, if at all. In fact, the field of
binocular single vision usually extends not less than 40 degrees from
the primary position in every direction.

Each of the various parallel movements of the eye appear to be governed
by a distinct nerve mechanism, there being one centre for movements to
the right, one for movements to the left, one for movements up, etc.

MOVEMENTS OF CONVERGENCE

In order to see an object at a nearby point, the eyes have to
converge—a movement affected by a simultaneous and equal contraction
of both internal recti. This movement may be combined with a vertical,
lateral or oblique parallel movement. Thus, when we wish to look at a
near object situated twenty degrees to our right, we first turn both
eyes twenty degrees to the right, then converge both equally, turning
the left a little more to the right and the right a little back toward
the left.

Convergence is governed by a distinct mechanism of the nerves, the
source of which has not been determined.

MOVEMENTS OF DIVERGENCE

In passing from a position of convergence to a position of parallelism,
the lines of sight separate or diverge. This movement of divergence
is a simultaneous, equal contraction of both externi; or, probably,
of both actions combined. The eyes may even diverge somewhat beyond
parallelism, as in overcoming prisms, base in, when looking at a
distant object.

VERTICAL DIVERGENCE

The amount by which the lines of sight can separate in a vertical
direction is very limited—at most but one or two degrees.

ORTHOPHORIA

The term orthophoria is used to denote an absolutely normal balance of
the extrinsic muscles, just as the term emmetropia denotes a normal
refractive condition. They are equally rare.

HETEROPHORIA

The term heterophoria includes all those conditions in which there is
a tendency to depart from normal balance, but which nature is able to
compensate for; while the term also includes the conditions in which
nature has been unequal to the task and an actual turning or squint has
occurred.

SUBDIVISIONS

The subdivisions of these terms at first reading appear complicated,
but prove simple enough on closer study, indicating only the direction
of the turning or tendency to turn. For instance:

Esophoria signifies _inward_ tendency.
Exophoria signifies _outward_ tendency.
Hyperphoria signifies _upward_ tendency.
Hypophoria signifies _downward_ tendency.
Cyclophoria signifies _tendency_ to torsion.
Esotropia signifies _inward_ turning.
Exotropia signifies _outward_ turning.
Hypertropia signifies _upward_ turning.
Hypotropia signifies _downward_ turning.
Cyclotropia signifies _actual_ torsion.

Combinations are describable in similar terms. A tendency of the right
eye to turn up and inward, is a “right hyperesophoria”; the left eye
to turn down and out, a “left hyperexophoria,” etc. Tendencies of both
eyes together are denoted by the terms which follow:

Anaphoria signifies an _upward_ tendency.
Kataphoria signifies a _downward_ tendency.
Dextrophoria signifies a _right_ tendency.
Laevophoria signifies a _left_ tendency.

CHAPTER XVII

SYMPTOMS OF HETEROPHORIA

These depend on the kind of error present as well as the degree and
widely vary.

In general, they may be said to fall into three classes—(1) defective
vision, (2) pain of greater or less degree—(3) reflex symptoms.

_Defective Vision._ The first class may be present, even though each
eye has a normal visual acuity; since, even when compensation is very
good, the brain gets the impression of two objects, nearly, though
not quite fused; and vision may be considerably worse with both eyes
together than with either eye singly.

When compensation is considerably impaired, the diplopia becomes more
and more persistent, till the brain finally makes choice of one image
as more satisfactory, entirely suppressing the other. Visual acuity
may not suffer in either eye; but vision being no longer binocular,
everything is seen in the flat, the judgments of depth and distance
being regularly more or less defective. While this is a tremendous
disadvantage in many occupations, people gradually and not infrequently
become accustomed to these visual defects and are not conscious of the
handicap.

_Pain._ It is quite different with the second set of symptoms, which
are always accompanied with pain. In fact, the character of the
subjective symptoms in refractive errors and muscular imbalance is so
similar that it is practically impossible to differentiate in many
cases.

In muscular asthenopia, however, in addition to becoming easily tired,
the patient often complains that letters seem to jump or run together
or he may contend that he sees double for an instant; or again that he
can “feel his eyes turn” involuntarily in their sockets. These pains
or conditions are sometimes present only during actual _use_ of the
eyes. At other times they persist for hours. In some cases, after days
or weeks of overstimulation, an explosion in migraine form occurs at
irregular intervals. This condition often lasts a day or two.

_Reflex Symptoms._ In the third and last case, there are other reflex
symptoms—such as dizziness, nausea, fainting, indigestion, insomnia
and pains in other portions of the body—sometimes stimulating organic
diseases.

The possibility of heterophoria as a factor in chorea, migraine,
neurasthenia and other diseases which may be primarily due to unstable
nerves, equilibrium is not to be forgotten. It is a notable fact that
when the fusion compensation fails so completely that one image is
entirely suppressed, or the diplopia is so great as to be overlooked,
the symptoms often cease entirely.

TREATMENT

The treatment of heterophoria depends on a careful study of each
individual case, but it cannot be too strongly emphasized that in the
great majority of cases the subjective symptoms disappear after a full
correction of the refraction is made.

In many cases, if the visual acuity in each eye be made normal, the
fusion impulse alone will be sufficient to restore compensation.

Many cases of esophoria result from overstimulation of the centers
for convergence and accommodation, made necessary by hyperopia and
astigmatism, entirely disappearing when glasses abolish the need of
accommodation. Cases of exophoria are sometimes due to the abnormal
relaxation of accommodation and convergence which secures the best
distant vision in myopia. Likewise the correction of myopia, by
increasing the far point, may diminish the amount of convergence
necessary for near vision.

Prisms for constant use are often prescribed, so placed as to help the
weak muscles and counteract the strong. For instance, in esophoria we
find the prism which, base in, will produce orthophoria for distance
and prescribe a quarter of it, base in, before each eye. While this
is very successful in some cases, the tendency in others is for the
externus to increase slightly from constant exercise in overcoming
the prism, while the internus decreases in proportion to the amount
of work of which it is relieved. Prisms for permanent use are very
beneficial in vertical deviations, since when the images are brought
on the same level they require much less effort to secure fusion; and
when prescribed base up or down, the effect secured is commonly an
unchanging one.

We sometimes take advantage of this tendency when we prescribe for
constant use weak prisms with the apex over the weak muscle, which
gradually becomes strong from the exercise of overcoming it. This plan
is effective only in patients who have a strong fusion impulse, and
the prism selected must be weak enough to be easily overcome. We can
accomplish the same effect by decentering the patient’s refraction
lenses.

For instance, a convex lens so placed that the visual line passes
the reverse will be the case if the lens is concave. The amount of
prismatic action depends on the strength of the lens and the amount
of decentering, the rule being that every centimeter of displacement
causes as many prism diopters as there are diopters in that meridian
of the lens. Thus +1 sphere, or cylinder axis 90, decentered one
centimeter outward, is equivalent to adding a one degree prism diopter
lens, base out.

DESTROPHORIA AND LAEVOPHORIA

These are terms denoting a condition in which both eyes are capable
of abnormal rotating toward the right or left, as the case may be.
The movement in the opposite direction is most common. The patient
can often rotate his eyes 60 degrees toward the right, and to perhaps
only 40 degrees to the left. His position of rest is parallel with his
visual lines, but to the _right_, in looking at objects directly in
front, he is much more comfortable with his head turned slightly to the
left.

It is difficult to account for, except on the theory that definite
movement of the eyes is rather to the right than to the left in most
occupations. The position of the paper in writing at a desk tends
toward dextrophoria; in reading, we move our eyes steadily from left
to right and then begin a new line by a single brief movement to
the left; the things that a man uses most—whether he be laborer or
student—are kept within reach of the right hand, and in referring to
them the eyes are constantly turned toward the right.

However, when these conditions result from other imbalances, they must
be treated more carefully. For instance, a patient whose right internus
is paralysed or congenitally defective on looking to the left, has
a cross diplopia which vanishes to the right; as a result, he soon
assumes a habit of carrying his head in this position. Ordinarily, this
will cause no discomfort; but if the left internus is so weak that it
cannot follow the right externus to its position of greatest ease, the
visual lines are evidently different and the case must be treated as an
exophoria.

If, on the other hand, the _left_ internus over-balances the right
externus, the condition is an esophoria and must be treated as such.

Similar reasoning applies to the conditions known as Anaphoria and
Kataphoria, in which the visual lines are parallel to each other but
directed up or down with regard to the horizontal plane of the body.

In the first, owing to congenital abnormalities, the eyes usually tend
upward and the individual must go about with his chin on his chest, so
that his eyes may look in front and yet remain in the position of rest.
In the second, the chin is held in the air and the body arched backward.

But, unless extreme, neither of these conditions causes more than
cosmetic difficulty and both should be undisturbed owing to the extreme
difficulty of securing the same operative effect on both eyes. Suitable
prisms are much more likely to be beneficial.

[Illustration: Supports for Holding The Ski-optometer

_Floor Stand_]

[Illustration: _Wall Bracket_]

[Illustration: _Chair Clamp_]

[Illustration: _Chair Attachment with Upright_

Choice may be made from any of the above. The Wall Bracket is
recommended, unless refractionist is provided with a specialist’s
chair, to which the Chair Attachment with Upright may be attached.]

*** End of this Doctrine Publishing Corporation Digital Book "Refraction and muscular imbalance" ***

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