Components of visual acuity loss in strabismus

Strabismus, the misalignment of the visual axis of one eye relative to that of the other eye, reduces visual acuity in the affected eye. Several processes contributing to that loss are: amblyopia, which results in a chronic acuity loss whether or not the fellow eye is viewing; strabismic deviation, which shifts the image of an acuity target onto more peripheral, and therefore less acute, retina when the fellow eye fixates; interocular suppression and binocular masking, which reduce visibility in the strabismic eye due to neural influences from the other eye. We measured the losses due to these processes in nine small-angle strabismic subjects. Amblyopia reduced acuity by a median of 34% relative to its value in subjects with normal binocular vision, and strabismic deviation produced a loss of 44%. Suppression and masking together reduced acuity by 20%, and therefore had substantially less effect than the other factors.