To investigate binocular interaction of visual acuity (VA) in patients with intermittent exotropia and its relationship with accommodative responses during binocular vision.

Prospective pilot study.

setting: Institutional. patient: Sixty-three patients with intermittent exotropia between 8 and 15 years of age. observation: Binocular VA and monocular VA were measured in sequence. Accommodative responses of both eyes were measured using the WAM-5500 autorefractor/keratometer (GrandSeiko) during binocular and monocular viewing conditions at 6 m. Accommodative responses during binocular vision were calculated using the difference between the refractive errors of binocular and monocular vision. main outcome measures: Binocular interactions of VA were categorized as binocular summation, equivalency, or inhibition. The prevalence of the 3 patterns of binocular interaction was investigated. Accommodative responses were correlated with differences between binocular VA and better monocular VA.

Most patients (38 patients; 60.3%) showed binocular equivalency. Binocular summation and inhibition were noted in 19 (30.2%) and 6 (9.5%) patients, respectively. Linear regression analysis revealed a significant correlation between binocular interaction and accommodative responses during binocular vision (P < .001). Accommodative responses significantly correlated with the size of exodeviation at distance (P = .010).

In patients with intermittent exotropia, binocular interaction is associated with accommodative response during binocular vision and the size of exodeviation, suggesting that accommodative convergence is a mechanism that maintains ocular alignment. Therefore, binocular interaction, especially binocular inhibition, can be a good indicator of diminishing fusional control in intermittent exotropia.