Chapter VIITHE BINOCULAR MUSCLE TEST
Directingthe patient’s attention to the usual muscle testing spot of light, theredMaddox rod should be placed in operative position before the eye, with the singlewhiteline or indicator on red zero (Fig. 15). The rods now lie in a vertical position.
Fig. 15—The Maddox rods placed vertically denote test for right or left hyperphoria, causing a horizontal streak to be seen by patient.
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.
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.”
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.).
Fig. 17—The horizontal streak caused by Maddox rod bisecting muscle testing spot-light for vertical imbalance, as patient should see it.
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 streakcuts throughthepoint of light, the refractionist instantly notes the absence of hyperphoria. Should the point of light and the red streaknotbisect, 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.
Fig. 18—The Maddox rods placed horizontally test esophoria or exophoria, causing a vertical streak to be seen by the patient.
Fig. 18—The Maddox rods placed horizontally test esophoria or exophoria, causing a vertical streak to be seen by the patient.
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 handlehorizontal (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.
Fig. 19—The phorometer handle placed horizontally denotes horizontal muscles are undergoing test for esophoria or exophoria indicated by “Es.” or “Ex.”
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 onthe 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.
Fig. 20—The vertical streak bisecting muscle testing spot-light for horizontal imbalance, as patient should see it.
Fig. 20—The vertical streak bisecting muscle testing spot-light for horizontal imbalance, as patient should see it.
It is considered best to make the binocular testbeforeregular 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.
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 tothe patient’s refraction and age, but they are generally accepted as safe.
There are four distinct methods for correcting muscular imbalance, each of which should be carried out in the following routine:
1.Optical correctionmade with spheres or cylinders, or a combination of both.2.Muscular exercisingor “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.
1.Optical correctionmade with spheres or cylinders, or a combination of both.
2.Muscular exercisingor “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 of the Ski-optometer, (Fig. 21) consists of a prism unit, having a total equivalent of thirty degrees. It is composed oftwo 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.
Fig. 21—Turning rotary prism’s pinioned handle gives prism value from zero to 30° as indicated by prism’s red line indicator.
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, basein. A rotation from zero to 10 outward would give a prism equivalent of ten degrees, baseout, 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, baseup. A rotation from zero downward to 10 would give a prism equivalent of ten degrees, basedown.
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.
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, theindicator 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.