Visually evoked response testing with a stimulator-ophthalmoscope. Macular scars, hereditary macular degenerations, and retinitis pigmentosa.

Visually evoked responses (VERs) were recorded from 47 patients under age 60 years with macular scars, hereditary macular degenerations, or retinitis pigmentosa. A hand-held, two-channel stimulator-ophthalmoscope was used to present to the central fovea a 1.5 degrees flickering stimulus centrally superimposed on a steady 10 degrees background. All 31 patients with visual acuity (VA) 20/50 or less had abnormal VERs; among patients with VA 20/25 to 20/40, all six with macular degenerations and five of ten with retinitis pigmentosa also showed abnormal VERs. Abnormal VERs were either out of phase or indistinguishable from noise. Sensitivity of the technique depended on a low ratio of stimulus to background retinal illuminance and the fact that the stimulus could be visualized by the examiner through the ophthalmoscope and maintained on the central fovea througout testing.