Light rise of the human electroretinogram is normal in retinitis pigmentosa

To determine if the electroretinogram (ERG) light rise is reduced below normal in patients with retinitis pigmentosa (RP) and whether it is greater in patients with smaller ERG.

Both eyes of 31 normal subjects and 59 subjects with RP had photopic ERGs on ISCEV standard and brighter backgrounds, before and after dark adaptation. Recordings <2.5 micro V were excluded.

Ratios of amplitudes before and after dark adaptation varied little. The b-wave averaged 1.88 (SD 0.41) in normal subjects and 1.66 (SD 0.62) in RP subjects, and a-waves averaged 1.44 (SD 0.42) and 1.31 (SD 0.73), respectively. None of eight t-tests were significant (<2.4). There was a positive (not negative) correlation between RP subjects' initial b-wave amplitude and light rise but not for a-waves. A-wave light rises were smaller.

Retinitis pigmentosa does not reduce the light rise of recordable ERG. The light rise of the ERG is larger in those RP subjects with larger initial b-waves. This confirms previous findings. The difference between a- and b-waves in RP suggests post-receptoral processes are involved.