It was unclear how the amplitude of the PhNR, evoked by the onset of a long-duration flash, PhNR
on, could reasonably be estimated from control records. Therefore, the change in amplitude at the time of the negative PhNR trough in control ERGs that was brought about by procedures that removed inner retinal responses were used as a surrogate estimate of PhNR
on.
Figure 7shows the PhNR amplitude produced by experimental glaucoma and TTX with the color combinations used in
Figure 6measured over a range of stimulus luminances. As seen for responses to brief flashes, the PhNR
on revealed by TTX and experimental glaucoma were similar, although the PhNR amplitude after TTX did not increase as monotonically with stimulus strength as with glaucomatous eyes in these long-flash experiments. The PhNR
on to the blue and red stimuli increased as a function of stimulus strength and first saturated at a stimulus luminance of approximately 15 cd/m
2, after which the amplitude with the blue stimulus continued to grow. The PhNR
on was smallest with the white on white stimuli, but with increasing stimulus luminance, the amplitudes increased and became similar to the PhNR
on recorded with the blue and red stimuli. For stimulus luminance up to approximately 20 cd/m
2, PhNR
on for the white on white and green on blue stimuli was significantly smaller than the PhNR
on recorded with the red and blue stimuli (
P < 0.05, repeated measures ANOVA). However, for any given color combination of a particular stimulus strength, there was no statistically significant difference (
P > 0.05. two-sample
t-test) in the PhNR
on estimated from the TTX and glaucoma experiments.