The association between anisometropia, amblyopia, and binocularity in the absence of strabismus

Purpose: First, to determine if thresholds exist for the development of amblyopia and subnormal binocularity with various types of anisometropia and to confirm or refute existing guidelines for its treatment or observation. Second, to delineate any association between the degree or type of anisometropia and the depth of amblyopia and severity of binocular sensory abnormalities. Methods: Four hundred eleven (411) patients with various levels of anisometropia, no previous therapy, and no other ocular pathology were evaluated. The effect of anisometropia (both corrected and uncorrected) on monocular acuity and binocular function was examined. Results: Spherical myopic anisometropia (SMA) of >2 diopters (D) or spherical hypermetropic anisometropia (SHA) of > 1 D results in a statistically significant increase in the incidence of amblyopia and decrease in binocular function when compared to non anisometropic patients. Increasing levels of SMA and SHA beyond these thresholds were also associated with increasing depth (and in the case of SHA, incidence as well) of amblyopia. Cylindrical myopic anisometropia (CMA) or cylindrical hyperopic anisometropia (CHA) of > 1.5 D results in a statistically significant increase in amblyopia and decrease in binocular function. A clinically significant increase in amblyopia occurs with > 1 D of CMA or CHA. Increasing levels of CMA and CHA beyond > 1 D were also associated with an increased incidence (and in the case of SMA, depth as well) of amblyopia. Conclusions: This study provides guidelines for the treatment or observation of anisometropia and confirms and characterizes the association between the type and degree of anisometropia and the incidence and severity of amblyopia and subnormal binocularity.