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

by Daniel Woolf

The Phorometer

As previously stated, it is practically impossible to accurately diagnose a case of muscular imbalance with trial-case prisms. For this reason the phorometer forms an important part of the equipment for muscle testing in the Ski-optometer, having proven both rapid and accurate. It consists of two five-degree prisms with bases opposite, each reflecting an object toward the apex or thin edge. The patient whose attention is directed to the usual muscle-testing spot of light, will see two spots.

Aside from the instrument itself, and in further explanation of the phorometer’s principle and construction, when two five-degree prisms are placed together so that their bases are directly opposite, they naturally neutralize; when their bases are together, their strength is doubled. Thus while the prisms of the phorometer are rotating, they give prism values from plano to ten degrees, the same being indicated by the pointer on the phorometer’s scale of measurements.

As a guide in dark-room testing, it should be noted that the handle of the phorometer in a vertical position is an indication that the vertical muscles are being tested; if horizontal, the horizontal muscles are undergoing the test.