Comparison of retinal nerve fiber layer thickness between monocular and alternating exotropia in patients with intermittent exotropia.

Purpose: To investigate differences in intraocular structure based on the presence or absence of fixation preference in children with intermittent exotropia (IXT) by comparing the thickness of the retinal nerve fiber layer (RNFL).

Methods: From October 2018 to March 2022, RNFL thickness was retrospectively analyzed using spectral domain optical coherence tomography. Participants had uncorrected visual acuity of 20/20, refractive errors close to emmetropia, and no anisometropia. The patients were divided into monocular and alternating exotropia groups through a cover-uncover test. The average and sectoral thickness of the RNFL in both groups were compared.

Results: The average global thickness and average thickness of each of the six sectors of the RNFL did not significantly differ between dominant and non-dominant eyes in the monocular exotropia group and between right and left eyes in the alternating exotropia group. The thickness did not significantly differ between the monocular exotropia group and the right or left eye of the alternating exotropia group. Interocular differences in RNFL thickness were negative in the monocular exotropia group (dominant eye-non-dominant eye) and positive in the alternating exotropia group (right eye-left eye) for the average, inferonasal, and inferior sectors, exhibiting statistically significant between-group differences (p = 0.019, p = 0.003, p = 0.023, respectively).

Conclusions: In children with IXT without obvious refractive error, there was a significant interocular difference in RNFL thickness of the average, inferonasal, and inferior sectors between monocular and alternating exotropia groups. The presence of fixation preference may affect RNFL thickness.