Rod and Cone Responses in Sex-Linked Retinitis Pigmentosa

Psychophysical and electrophysiological testing are used to examine a family with sex-linked retinitis pigmentosa. Marked changes in the electroretinogram (ERG) precede any abnormalities visible with the ophthalmoscope. Both cone and rod responses are reduced in amplitude and delayed in implicit time. Cone responses are detectable after rod responses have disappeared. When rod function can be measured, scotopic luminosity curves and ERG responses to scotopically balanced lights indicate a normal rod action spectrum. The disease in males is widespread, whereas carrier females show loss of retinal function only in limited areas. Comparison of findings in carrier females with those in affected males provides support for the Lyon hypothesis.