Foveal cone dysfunction syndrome.

Our objective was to describe and expand the clinical spectrum of a rarely detected, previously reported photoreceptor disorder restricted to the foveal cones. Three patients with bilaterally decreased acuity and hemeralopia were examined to exclude a structural, vascular, inflammatory, or degenerative process. Each patient underwent a full neuroophthalmic examination, including full-field and focal cone electroretinogram (ERG). All three patients had normal-appearing fundi, mild dyschromatopsia, central or paracentral visual field depressions, normal full-field photopic and scotopic ERGs, and markedly reduced focal, foveal cone ERG responses. One patient had a ring scotoma and an asymptomatic family member with abnormal full-field and focal cone ERG. The syndrome of acquired foveal cone dysfunction presents as a bilateral, painless, progressive central visual loss with minimal or absent fundus changes. It eludes diagnosis until focal, foveal cone ERG is performed.