The range of zero-associated phoria in an asymptomatic clinical population.

The clinical concept of the range of zero-associated phoria is developed, and normative data for this range are presented based on a clinical study of 201 asymptomatic patients. The relation of patient age, sex, and amount of near lens addition to this range is examined. The range at far is not related to patient age or sex. The range at near appears to bae independent of patient age, sex, and the amount of near addition required by presbyopes.