Retinitis pigmentosa and allied diseases: applications of electroretinographic testing.

Electroretinograms (ERGs) have provided criteria for establishing the diagnosis of retinitis pigmentosa in early life even at a time when fundus abnormalities visible with the ophthalmoscope are minimal or absent. Patients with widespread progressive forms of retinitis pigmentosa have shown not only reduced amplitudes but also delays in cone or rod b-wave implicit times, or both, while patients with self-limited sector retinitis pigmentosa or stationary forms of night blindness have had reduced amplitudes with normal b-wave implicit times. In families with retinitis pigmentosa ERGs can be used not only to identify which patients are affected but also to establish which patients are normal as those patients, age 6 and over, with normal cone and rod amplitudes and normal cone and rod b-wave implicit times have not been observed to develop primary retinitis pigmentosa at a later time. ERGs from patients with retinitis pigmentosa and allied night blinding disorders are presented to show their usefulness in genetic typing, documenting natural; histories, and defining possible pathogenetic mechanisms. The potential application of the ERG in evaluating the efficacy of therapeutic trials is also considered.