A simplified method for analyzing data from the three-step test.

To the Editor. —In 1958, Parks 1 described a three-step test to ascertain which muscle is responsible for a cyclovertical imbalance. The first step narrowed the possibilities to four muscles; the second step excluded two of those four muscles; and the final step, the Bielschowsky head-tilt test, indicates which of the two muscles that remain is the weak muscle. During a busy clinical examination, it can be difficult to concentrate on the raw data that are obtained from the three-step test. A series of logical steps will help practitioners analyze that data quickly and efficiently (Figure). First, all vertical deviations from the primary position should be defined in terms of a hyperdeviation; that is, it should be called a right hyperdeviation (instead of a left hypodeviation). Second, if the hyperdeviation increases in the gaze that is directed to the same side as the hyperdeviation, the palsied muscle is assumed to