Early detection of central visual function decline in cone-rod dystrophy by the use of macular focal cone electroretinogram

PURPOSE. To evaluate macular focal cone ERG (fERG) as a tool for reliable and early detection of central retinal function decay in cone-rod dystrophy (CRD). METHODS. A retrospective study of the time course of fERG amplitude and its relation to visual acuity alterations was performed in 47 CRD patients followed yearly for 6.0 ± 3.1 years. Macular focal cone ERG was evoked by a flickering uniform red field overlaying the central 18° of visual field. RESULTS. Macular focal cone ERG follow-up allowed a clear-cut identification of CRD patients as stationary or progressive, in agreement with visual acuity follow-up. In all progressive patients, fERG declined whenever visual acuity declined, and-in 50% of the cases-fERG loss anticipated acuity loss of several years. CONCLUSIONS. Macular focal cone ERG represents a sensitive assay to detect, categorize, and follow the progression of central retinal dysfunction in CRD. Its use as a diagnostic tool in CRD may help anticipate, for an individual patient, the likelihood and rate of further disease progression before visual acuity loss has occurred.