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

by Daniel Woolf

Made with Both Rotary Prisms

While the previously described binocular muscle test made with the phorometer and Maddox rod, only determines the existence and amount of esophoria, exophoria, and hyperphoria, neither the faulty nor the deviating muscle is located, hence a monocular muscle test is essential in order to determine whether the muscles of the right or left eye are faulty. Furthermore, an imbalance may possibly be due to either a faulty muscular poise, or lack of nerve force in one or both eyes. A “duction test” should accordingly be made of each muscle of each eye separately, followed by a comparison of the muscular pull of both eyes collectively.

These tests are commonly termed adduction, abduction, superduction and subduction, and are defined in the order named. They include tests of the vertical and horizontal muscles of each eye, made individually by means of the rotary prisms, each being placed before the eye undergoing the test.