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 6metersmethods: fifty subjects with distance corrected or uncorrected visual acuity of 6/6 and orthophoriawithout history of amblyopia, strabismus or any ocular pathology were recruited and distancestereoacuity was measured by howard-dolman test before and after introducing 2, 4, 6 and 8δbase 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) prismscompared 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 sameamount (p=0.007).conclusion: induced heterophoria at distance of 6 meters reduced stereoacuity measured bymodified howard-dolman test. greater than 4δ of induced esophoria had statically and clinicallyadverse effect on distance stereoacuity.