Binocular visual acuity in intermittent exotropia: role of accommodative convergence.

PURPOSE

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

DESIGN

Prospective pilot study.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.