Strabismus, anisometropia, and amblyopia

Abstract

Anisometropia per se does not cause squint. Comparison between forty non-squinting hypermetropic anisometropes and 53 squinting hypermetropic anisometropes showed that the better eyes of the first group were significantly less ametropic than those of the second group. There was no significant difference in the amount of anisometropia, the incidence of astigmatism, or the sex ratio of the two groups. Patients in the first group were, in general, much older than those in the second group and had not usually been refracted under full cycloplegia, so that only an estimate of their refractive state at the age of 7 years, the "base-line" to which all cases were calculated, was possible. Squint and amblyopia were very rare in anisometropic myopes. The findings in the small group of antimetropes are discussed. The term "anisometropic amblyopia" is suggested to describe a common and important clinical entity which is independent of strabismus. Its treatment by occlusion at least until the age of 13 years is possible. The absence of squint in many cases of anisometropia even with dense amblyopia suggests the presence and importance of peripheral fusion. Because of their larger Panum's areas the peripheral retinae will retain their ability to fuse in spite of aniseikonia or unequal clarity of images which, in the central area, would cause "suppression" or "disuse" amblyopia. Full correction of their anisometropia was well tolerated by children, bilateral myopes, and all patients who no longer retained ability to accommodate; hypermetropes who still retained accommodative power preferred their spectacles to have equal spheres, or spheres differing less than the full amount of the spherical anisometropia, probably because their more ametropic eyes had learned to exert, constantly, an extra accommodative tone. Anisohypermetropia may be decreasingly latent as age advances. A simple "subjective binocular test" can be used to decide the advisability of a full anisometropic correction. For example, each eye separately in a patient aged 39 years achieved 6/6 with right D sph. and left sph., but the line looked clearer binocularly when a - 0-75 D sph. was added to the left eye. Hence the glasses prescribed were D sph. in the right eye and 25 D sph. in the left. The problems of the correction of axial, refractive, and mixed anisometropia are mentioned in relation to aniseikonia and possible relative differences in inter-cone distances at the maculae.