Abnormal dark-adapted electroretinogram in Best's vitelliform macular degeneration.

It is generally well accepted that in Best's vitelliform macular degeneration (BVMD) the electroretinogram (ERG) is normal whereas the electro-oculogram (EOG) is markedly abnormal. We describe a patient in whom BVMD was suspected on the basis of the clinical findings, EOG and family history (one of her daughters had the typical vitelliform lesion). However, her dark-adapted ERG was markedly abnormal. Similar anomalies were found in the dark-adapted ERG of the daughter. While the temporal features of the various ERG waves were well preserved, a substantial decrease in the amplitude of specific segments of the ERG signal was observed. A similar decrease in the amplitude of the oscillatory potentials was also found. We believe that this unusual combination of BVMD and abnormal dark-adapted ERG may be due to the reported reduced penetrance and variable expressivity of the BVMD gene(s).