Refraction and muscular imbalance, as simplified through the use of the ski-optometer

by Daniel Woolf

Superduction

Superduction, sometimes termed sursumduction, is the relative power of the superior recti to turn the eyes upward. Prism power base down and apex up is employed. To test superduction, the rotary prism should be placed in position with the two cyphers lying horizontally, with the handle pointed vertically ([Fig. 23]). The patient’s attention should again be directed to the large letter “E”, and the indicator or red line should be rotated downward from zero. The highest prism power that the patient will accept before the object appears to double in the vertical plane will indicate the degree of right superduction. This should be recorded accordingly. Conditions of this kind do not usually exceed two or three degrees. The test, however, should be repeated several times before the final result is recorded, as indicated in [Fig. 24]. The amount of superduction ranges from 1 to 4 prism diopters. The normal average is 2.

Fig. 23—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.