Clinical comparison of the zone of clear single binocular vision with the zone of zero-associated phoria

Normative data comparing the zone of zero-associated phoria (ZZAP) with the zone of clear single binocular vision (ZCSBV) are presented based on a clinical study of 156 asymptomatic patients. No statistically significant relations were found between zone difference and patient age, sex, and amount of near lens addition in the case of presbyopes.