The effects of experimentally induced anisometropia on stereopsis

Purpose: To determine the effects of experimentally induced anisometropia o n stereopsis in healthy adults to assess the potentially detrimental effect s of uncorrected anisometropia on the development of stereoacuity during ch ildhood. Methods: Twenty-one healthy adult volunteers ranging in age from 22-34 year s (mean: 27 years) and free of ocular disease participated in the study. Fo ur different types of anisometropia (unilateral myopia, unilateral hyperopi a, or unilateral astigmatism [90 degrees or 45 degrees]) were induced in ra ndom order by placing trial lenses over the right eye in 1 diopter (D) incr ements ranging from 1-3 D. Stereoacuity was measured using the Titmus stere otest with patients placing the cross-polarizing stereoacuity glasses over their lenses or trial frames. Results: Stereoacuity levels were reduced in proportion to the degree of an isometropia in all patients. One diopter of spherical anisometropia reduced stereoacuity to an average 57-59 are seconds; 1 D of cylindrical anisometr opia reduced stereoacuity to an average 51-56 are seconds. Three diopters o f anisometropia, regardless of type, produced a marked reduction of stereoa cuity in all patients. Conclusions: Low levels of anisometropia, both spherical and astigmatic, ca n have potentially significant adverse effects on high-grade binocular inte raction in adults. Foveal suppression, which is directly related to the deg ree of anisometropia, may be responsible for the loss of stereopsis. The da ta suggest the effects of anisometropia on stereopsis should be considered in the empiric correction of anisometropic refractive errors in children.