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.