The effects of experimentally induced anisometropia on stereopsis

To determine the effects of experimentally induced anisometropia on stereopsis in healthy adults to assess the potentially detrimental effects of uncorrected anisometropia on the development of stereoacuity during childhood.

Twenty-one healthy adult volunteers ranging in age from 22-34 years (mean: 27 years) and free of ocular disease participated in the study. Four different types of anisometropia (unilateral myopia, unilateral hyperopia, or unilateral astigmatism [90 degrees or 45 degrees]) were induced in random order by placing trial lenses over the right eye in 1 diopter (D) increments ranging from 1-3 D. Stereoacuity was measured using the Titmus stereotest with patients placing the cross-polarizing stereoacuity glasses over their lenses or trial frames.

Stereoacuity levels were reduced in proportion to the degree of anisometropia in all patients. One diopter of spherical anisometropia reduced stereoacuity to an average 57-59 arc seconds; 1 D of cylindrical anisometropia reduced stereoacuity to an average 51-56 arc seconds. Three diopters of anisometropia, regardless of type, produced a marked reduction of stereoacuity in all patients.

Low levels of anisometropia, both spherical and astigmatic, can have potentially significant adverse effects on high-grade binocular interaction in adults. Foveal suppression, which is directly related to the degree of anisometropia, may be responsible for the loss of stereopsis. The data suggest the effects of anisometropia on stereopsis should be considered in the empiric correction of anisometropic refractive errors in children.