Pattern electroretinograms were recorded to phase-reversing checkerboard stimuli with DTL electrodes under conditions close to those of the ISCEV pattern electroretinogram guidelines. Both transient (2 reversals/s) and steady-state (16 reversals/s) stimulation was used. The check sizes were 0.4 degree, 0.8 degree and 16 degrees; the mean luminance 45 cd/m2, the contrast 98%, and the field size 32 degrees x 27 degrees. In 42 eyes of 21 subjects, measurements were repeated at the same time of day after 1 week. For each eye, the intersession coefficient of variation was calculated as a measure of reproducibility. We found a coefficient of variation (+/- standard deviation) of 7% +/- 5% for the amplitude of the steady-state pattern electroretinogram, 9.5% +/- 7% for the transient pattern electroretinogram and 1.5% +/- 2% for the latency of the transient pattern electroretinogram. To assess the diurnal variability, during a 15-h period, three pattern electroretinograms were recorded in 10 subjects. No relationship was found between the P50 latency and the time of day. However, the mean amplitude showed a maximum in the morning (9:30 am) and a minimum in the afternoon (2:30 pm). This small effect (about 7%, p < 0.001) was more pronounced for N95 and steady-state amplitudes than for P50 amplitudes (p < 0.01). Diurnal contributions to the pattern electroretinogram ranged between 3% and 10%. We conclude that pattern electroretinogram amplitude reproduces within +/- 10% with a probability of 70%. The effect size of the diurnal variation is similar and might be relevant for longitudinal studies.

These data establish distinct expression profiles of NR subunits in human retinal ganglion cells and suggest the development of specific NR ligands to reduce excitotoxic retinal ganglion cell loss.

It was possible to record ERGs and PERGs in pigs. However, the ERG amplitudes were small; PERG amplitudes were even smaller in both groups and cannot be reliably recorded. A problem for both ERG and PERG was the high intra-individual and interindividual variability. Therefore, only very extensive damage to the retina by vitrectomy or Er:YAG laser treatment might lead to a significant change in the ERG or PERG amplitudes.

The pattern ERG (PERG) is used as an indicator of retinal ganglion cell function. Up to now, reports on the reproducibility of the PERG have been contradictory. We investigated the reproducibility under the conditions of the forthcoming ISCEV guidelines for the PERG. We simultaneously recorded the PERG and VEP in 42 eyes of 21 subjects to phase-reversing checkerboard stimuli with DTL electrodes. Both transient (2 rps) and steady-state (16 rps) stimulation was employed. The check sizes were 0.4 degree, 0.8 degree and 16 degrees, the mean luminance 45 cd/m2, the contrast 98%, and the field size 32 degrees x 27 degrees. Measurements were repeated at the same time of day after 1 week. In addition, we compared two different electrode positions in 16 eyes: (1) across the cornea along the lower lid; and deep in the conjunctival sac. With position (1) the amplitudes were found to be higher by 20% than (2). We calculated the coefficient of variation (CV) of amplitude as a measure of reproducibility. CV was 7 +/- 1% for the steady-state PERG, 9 +/- 1% for the transient PERG, 12 +/- 2% for the steady-state VEP and 14 +/- 3% for the transient VEP. For the latency of the PERG, the intersession CV was found to be 1.5%. Amplitude reproducibility was somewhat higher under steady-state as compared to transient stimulation; we attribute this to the high noise rejection of the Fourier analysis. Altogether, the amplitude reproducibility of the PERG is somewhat higher than that of the VEP.

Cerestat, memantine and riluzole have a neuroprotective effect--reducing excitotoxic damage of retinal neurons. The relative drug potencies cannot be directly compared, because of differences in dosage and the route of administration.