Abstract: Objective To analyze the abnormal vertical fixation disparity which coexists with intermittent exotropia (IXT) and its influence on stereoacuity. Design Case control study. Participants 104 newly diagnosed IXT patients and 128 controls in Beijing Tongren Hospital from Jul 2016 to Feb 2017 were involved. Methods Perceptual eye position (PEP) test was performed on normal controls to get normal range (<x+1.64 s). The IXT patients were divided into two groups according to whether their vertical PEP exceeded normal range abnormal vertical PEP (group and normal vertical PEP group). Stereoacuity was measured for both near and medium distances. The differences of stereoacuity were compared between the two groups. Main Outcome Measures PEP test, stereoacuity measured for both near and medium distances. Results The near and medium distance stereopsis were better in normal vertical PEP group (2.21±0.34, 2.09±0.23) than abnormal vertical PEP group (2.40±0.44；2.25±0.31) (t=-2.43， P=0.02；t=-2.97， P<0.01, respectively). However, no statistic differences were found between the two groups in age (P=0.19), interocular difference in spherical equivalent (P=0.12), near and far horizontal deviation (P=0.53, 0.38), break point of fusional divergence (P=0.70) and fusional vergences (P=0.94), fusion range (P=0.70). Conclusion Abnormal vertical fixation disparity coexisting with IXT may aggravates the damage of stereoacuity. (Ophthalmol CHN, 2023, 32: 228-232)

Key words: vertical fixation disparity, intermittent exotropia, perceptual eye position