PURPOSE: Because palpebral fissure asymmetry in horizontal gaze is reportedly common in otherwise normal persons, we determined the prevalence of physiologic palpebral fissure asymmetry for primary and horizontal gazes. METHODS: We measured the palpebral fissure height of both eyes of 88 healthy white subjects. Measurements were obtained with high-resolution videography, with the eyes in primary position, in 45-degree right gaze, and in 45-degree left gaze. RESULTS: Of the 88 subjects, 36 (41%) were male and 52 (59%) were female. The ages ranged from 12 to 50 years, with a mean of 32.5 ± 9.0 years. When a criterion of equal to or greater than 1 mm was used, the prevalence of physiologic palpebral fissure asymmetry was 5.7% (five of 88) in primary gaze, 18.2% (16 of 88) in right gaze, and 14.8% (13 of 88) in left gaze. The largest observed palpebral fissure asymmetry was 2.1 mm. After correcting for any existing fissure asymmetry in primary gaze, two-tailed trivariate analysis of variance showed that the fissure of the adducting eye tended to be wider. The mean increase in the palpebral fissure of the adducting eye was 0.12 mm for right gaze (P = .052) and 0.13 mm for left gaze (P = .034). Additionally, a γ2 test indicated that the occurrence of wider adducting eye in both right and left gazes was highly significant (P = .0023). CONCLUSIONS: In this sample of white subjects, palpebral fissure height asymmetry increased in horizontal gaze to the right and to the left, which is in part because of a tendency of the adducting eye to widen slightly. In contrast to previous reports, the prevalence of palpebral fissure asymmetry was low, and the abducting eye did not widen significantly.
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