The association between nonstrabismic anisometropia, amblyopia, and subnormal binocularity

Purpose: To determine if thresholds exist for the development of amblyopia and subnormal binocularity with various types of anisometropia and to compa re these with existing guidelines for the treatment or observation of aniso metropia, Design: The records of all previously untreated patients evaluated for isol ated refractive error during a 42-month period were reviewed to assess the association between anisometropia, amblyopia, and subnormal binocularity. Participants: Three hundred sixty-one (361) patients with anisometropia and 50 nonanisometropic control participants, examined over a 42-month period, with no history of treatment for refractive error, amblyopia, or other ocu lar pathologic characteristics were evaluated. Methods: Uncorrected visual acuity in each eye, monofixation response, and degree of stereopsis were recorded for each patient. Patients with unequal or subnormal uncorrected visual acuity were retested with cycloplegic refra ction, If the visual acuity was still abnormal, patients were retested whil e wearing spectacles. Main Outcome Measures: Degree and type of anisometropia were compared with incidence and severity of amblyopia and subnormal binocularity. Results: Spherical myopic anisometropia (SMA) of more than 2 diopters (D) o r spherical hypermetropic anisometropia (SHA) of more than 1 D results in a significant increase in the incidence of amblyopia and decrease in binocul ar function when compared with nonanisometropic patients (P = 0.05), Increa sing levels of SMA and SHA beyond these thresholds result in increased inci dence and severity of amblyopia. Cylindrical myopic anisometropia (CMA) or cylindrical hyperopic anisometropia (CHA) of more than 1.5 D results in a s ignificant increase in amblyopia and a decrease in binocular function (P = 0.05). Levels of CMA and CHA more than 1.5 D result in an increased inciden ce and severity of amblyopia, Conclusions: This study supports existing guidelines for the treatment or o bservation of anisometropia and characterizes the association between the t ype and degree of anisometropia and the incidence and severity of amblyopia and subnormal binocularity. Ophthalmology 2001;108:163-171 (C) 2001 by the American Academy of Ophthalmology.