Comparison of Contrast Sensitivity between Alternating and Monocular Intermittent Exotropia

Purpose: To determine if contrast sensitivity varies between alternating and monocular intermittent exotropia.Methods: The study conducted a retrospective analysis of medical records for children aged 5-9 years with intermittent exotropia who had uncorrected visual acuity of 1.0 or better, a spherical equivalent of ± 1.50 diopters (D) or less, and anisometropia of 1.00 D or less. Patients were categorized into two groups using the cover-uncover test: an alternating group without fixation preference and a monocular group with fixation preference. Contrast sensitivity tests were performed on each eye under mesopic and photopic conditions with glare. In the alternating group, eyes were classified as right or left while in the monocular group the non-deviated eye was labeled dominant and the deviated eye was non-dominant.Results: The study included 53 patients with 31 in the alternating group and 22 in the monocular group. In the alternating exotropia group, the left eye demonstrated significantly better contrast sensitivity at 1.1 cycles per degree (cpd) under mesopic conditions (<i>p</i> = 0.043), with no significant differences noted under other conditions. In the monocular exotropia group, dominant eyes exhibited significantly better contrast sensitivity at 10.2 cpd under mesopic conditions (<i>p</i> = 0.046) and at 1.1 cpd under photopic conditions (<i>p</i> = 0.031). No significant differences were observed in the interocular contrast sensitivity between the monocular and alternating groups across all spatial frequencies under both mesopic and photopic conditions.Conclusions: Pediatric patients with monocular intermittent exotropia displayed no significant differences in contrast sensitivity between dominant and non-dominant eyes except at certain frequencies. Additionally, there were no significant interocular contrast sensitivity differences between the monocular and alternating groups suggesting that contrast sensitivity tests may not be effective for determining the dominant eye in these conditions.