effect of induced heterophoria on distance stereoacuity by using the howard-dolman test

purpose : to evaluate the effect of induced esophoria and exophoria on distance stereoacuity at 6 meters methods : fifty subjects with distance corrected or uncorrected visual acuity of 6/6 and orthophoria without history of amblyopia, strabismus or any ocular pathology were recruited and distance stereoacuity was measured by howard-dolman test before and after introducing 2, 4, 6 and 8δ base in and base out to induce esophoria and exophoria, respectively. results : although the decrease in stereoacuity was not significant by introducing 2δ base in prism (p=0.062), but it was significant statistically by introducing 4 and 6δ base in (p=0.002, p=0.026, respectively) and 2, 4, 6, 8δ base out (p=0.042, p<0.001, p<0.001, p<0.001, respectively) prisms compared with orthophoric position. there was no significant difference between stereoacuity in 2δ and 4δ induced esophoria with 2δ and 4δ induced exophoria (p=0.696, p=0.677, respectively), but 6δ induced esophoria decreased stereoacuity more than induced exophoria of the same amount (p=0.007). conclusion : induced heterophoria at distance of 6 meters reduced stereoacuity measured by modified howard-dolman test. greater than 4δ of induced esophoria had statically and clinically adverse effect on distance stereoacuity.   iranian journal of ophthalmology 201224(1):25-30 © 2012 by the iranian society of ophthalmology