Optical coherence tomography findings in occult macular dystrophy

PURPOSE: To determine the basis for unexplained visual acuity loss in selected patients. DESIGN: Observational study of patients with unexplained reduced visual acuity. METHODS: We used optical coherence tomography (OCT) to evaluate foveal structure in eight patients. These patients had corrected visual acuities of 20/25 to count fingers in one or both eyes and a normal ocular examination. We recorded foveal cone electroretinograms (ERGs) as an objective measure of foveal function. RESULTS: Seven patients showed reduced foveal thickness associated with thinning of the outer nuclear layer (ONL), and five of these patients also had reduced foveal cone ERGs. One patient had normal tomograms and reduced foveal ERGs. CONCLUSIONS: Unexplained reductions in visual acuity may result from photoreceptor loss or foveal malfunction without photoreceptor loss, which are indicators of occult macular dystrophy. OCT and the foveal cone ERG together appear to be sufficient to identify the basis for visual acuity loss in these patients.