Photopic electroretinogram implicit time in retinitis pigmentosa.

While the implicit time of cone responses in the electroretinogram (ERG) has been suggested to have some clinical implications in retinitis pigmentosa (RP), its evaluation is not always easy in cases of typical RP because of the small amplitudes of the responses. An intense flash stimulus would be expected to improve the recordability of photopic ERG, which represents the cone responses. However, the implicit time in normal eyes has been shown to be delayed with increased stimulus intensity. Therefore, we evaluated photopic ERGs to a white flash stimulus of 3 different intensities as well as to a red flash in 14 cases of typical RP. The recordability of the response to white flash improved with the increased intensity of the stimulus. Most RP cases showed prolonged implicit time compared with that in normal eyes to each flash stimulus. Some patients who showed exceptionally normal or mildly delayed implicit time were considered to have good prognosis since they had noticed night blindness at an older age and most of their rod response in ERG was recordable.