Purpose:

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

Methods:

Sixty-seven patients with intermittent exotropia of 8 years or older were included. Binocular visual acuity (BVA) and monocular visual acuity (MVA) were measured in sequence. Accommodative responses of both eyes were measured using the WAM-5500 autorefractor/keratometer (GrandSeiko, Fukuyama, Japan) 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 visual acuity 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 BVA and better MVA.

Results:

Most patients (41 patients, 61.2%) showed binocular equivalency. Binocular inhibition and summation were noted in 6 (9.0%) and 20 (29.9%) 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 angle of exodeviation at distance (p = .002).

Conclusions:

In patients with intermittent exotropia, binocular inhibition is associated with increased accommodation and a larger angle of exodeviation, suggesting that accommodative convergence is a mechanism that maintains ocular alignment. Thus, BVA inhibition may be attributed to diminishing fusional control in patients with intermittent exotropia.