Fixation disparity analysis of oculomotor imbalance.

A device and method for measuring forced vergence fixation disparity curves in clinical situations are described. Phoria, vergence, and fixation disparity are measures of different functions of the oculomotor system. In decreasing order of diagnostic effectiveness, four features of the fixation disparity curve are curve type, slope, Y-intercept, and X-intercept. Patients with exophoria and non-Type I curves are likely to have ocular discomfort. The steeper the curve, the more likely the patient is to have symptoms. However, Type IV curves are usually flat, and many of these patients do have symptoms. Patients with Type I curves respond well to visual training, but those with Type II curves generally need lenses or prisms to obtain relief. The Y-intercept gives information that is particularly useful in exophoric patients. A complete analysis of the oculomotor system requires measurement of both phoria/vergence and fixation disparity.