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Phoria, vergence, and fixation-disparity were measured at near working distances for a nonclinical sample of 3rd-yr optometry students. A questionnaire divided the sample into 33 symptomatic and 44 asymptomatic subjects. Discriminant analysis was used to determine which clinical measures best predicted the group to which each subject belonged. Sheard's criterion was a good discriminator for exo deviations, and a variant of Percival's criterion was good for eso deviations. Fixation-disparity variables proved to be valuable diagnostically. The best fixation-disparity measures were the curve slope, curve type, and amount of fixation disparity.
Sheedy et al. (Sun,) studied this question.