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.