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

by Daniel Woolf

Subduction

Subduction, sometimes termed infraduction or deorsumduction, is the relative power of the inferior recti to turn the eyes downward. Prism power base up and apex down is employed. To test subduction, the rotary prism should be operated with zero graduations placed horizontally, as in the superduction test ([Fig. 23]), but the indicator should be slowly rotated in the reverse direction, or upward from zero. With the patient’s attention again directed to the large letter “E,” or the Greek cross, the strongest degree prism thus secured without diplopia will indicate the right subduction. The amount of subduction ranges from 1 to 4 prism diopters. The normal average is 2.

Any difference between superduction and subduction, usually denoting the existence of hyperphoria, should be given careful consideration.