Anisometropia and binocularity

Purpose: To determine the effects of experimentally induced anisometropia on binocular function in healthy adults as a means of assessing the potentially detrimental effects of uncorrected anisometropia on binocular development in childhood. Methods: Nineteen adults with normal binocularity, ranging in age from 26 to 59 years, were studied. Unilateral myopia, hyperopia, or astigmatism (at 90° or 45°) was induced in each subject using trial lenses. Sensory status then was assessed by measuring stereoacuity, Worth four-dot fusion, and Bagolini lens response. Results: All subjects showed a decline in binocular function with increasing levels of anisometropia. Foveal suppression was evident on the Worth four-dot test, and increased in proportion to the anisometropia. Stereoacuity was similarly degraded by the induced anisometropia, with some subjects showing significant loss of stereoacuity with as little as 1 diopter of spherical anisometropia. Bagolini lens responses were binocular in almost all patients, although occasional abnormalities were found. Conclusions: Relatively low degrees of anisometropia may cause significant abnormalities in high-grade binocular visual functions in adults. The potential effects of uncorrected anisometropia on binocularity in children require further investigation, but should be considered in developing guidelines for the empiric correction of refractive errors.