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The Degree of Image Degradation and the Depth of Amblyopia

From the College of Optometry, University of Houston, Houston, Texas.

PURPOSE. To determine whether the depth of monocular form-deprivation amblyopia is dependent on the degree of retinal image degradation.

METHODS. Chronic monocular form deprivation was produced in nine infant rhesus monkeys by securing one of three different strengths of diffuser spectacle lenses in front of the treated eye and a clear zero-powered lens in front of the fellow eye. Three infant monkeys reared with plano lenses in front of both eyes provided control data. The treatment lenses were worn continuously from approximately 3 weeks of age for periods ranging between 11 and 19 weeks. When the monkeys were approximately 18 months of age, psychophysical procedures were used to measure the effects of the rearing procedures on the spatial contrast sensitivity function for each eye.

RESULTS. The treated eyes of all nine diffuser-reared monkeys showed contrast sensitivity deficits that were indicative of amblyopia. On average, the interocular grating acuity difference increased systematically from 0.6 octaves for the weakest diffuser lens to 2.3 ± 0.7 and 3.5 ± 0.8 octaves for the intermediate and strongest diffuser lenses, respectively. There was a close correspondence between the magnitude of the amblyopic deficits and the reduction in retinal image contrast produced by the diffuser lenses.

CONCLUSIONS. The results demonstrate that the depth of monocular, nonstrabismic amblyopia is strongly influenced by the degree of retinal image degradation experienced early in life.

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