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.
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.
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.