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.]