Dominant retinitis pigmentosa with reduced penetrance. Further studies of the electroretinogram.

Full-field electroretinograms (ERGs) were recorded after a ten-year interval from four affected patients in a family with dominant retinitis pigmentosa with reduced penetrance; all patients showed decreases in amplitude. Cone ERGs from affected patients (aged 11 to 15 years) in this family as well as from affected patients of comparable ages from two other families with this genetic type, were normal or slightly reduced in amplitude and substantially delayed in b-wave implicit time. In one family, an asymptomatic older patient, representing an apparent skipped generation, showed abnormal full-field cone and rod ERGs that differed in implicit times from those of young affected patients. Evidence is presented to support the idea that the abnormal full-field cone ERGs recorded from young affected patients are due to an abnormal extrafoveal cone contribution to their full-field responses.