Contrary to the reaction in adult rats, juvenile rats exposed to the same bright environment for 3 (P14–P17 exposure interval) consecutive days did not develop significant ERG anomalies, irrespective of the ERG component considered (
Figs. 1G 2B , second tracing;
Table 1 ;
P > 0.05). Increasing the light exposure to 6 days (P14-P20;
Fig. 1H ) reduced the amplitude of the mixed (rod-cone) a- and b-waves to 51% (
P < 0.001) and 67% (
P < 0.01) of control, respectively
(Table 1) , but the rod
V max and the cone b-wave
(Fig. 2B)were not significantly attenuated. As the exposure interval lengthened, there was a gradual attenuation of the ERG signal (scotopic ERG,
Figs. 1I IJ 1K ; photopic ERG,
Fig. 2B ;
Table 1 ). After the longest exposure regimen tested (P14–P28), the amplitude of the mixed (rod-cone) a-wave was less than 16% of normal whereas that of the mixed (rod-cone) b-wave, rod
V max and cone b-wave were 44%, 48%, and 54% of normal, respectively (
P < 0.001;
Table 1 ). Interestingly, compared with adults exposed for 6 days to the bright, luminous environment, juvenile rats exposed for the same duration still produced ERG responses, albeit significantly smaller than normal. The extent of these reductions depended on the age at which the exposure started, as exemplified in
Figure 1and in
Table 1 . For example, 6-day exposure between P28 and P34 generated significantly more severe retinopathy (according to ERG measurements) than that obtained after 6-day exposure between P14 and P20 (reductions to 3% and 51% of the control value for the a-wave and to 11% and 67% for the b-wave during P28–P34 and P14–P20, respectively). Similarly, 6-day exposure between P28 and P34 caused more severe retinopathy than that obtained after 8-day exposure between P20 and P28 (reduction to 17% of the control value for the a-wave and to 31% for the b-wave after P20–P28 exposure). Irrespective of the duration of exposure (adults) or the exposure regimen considered (juvenile), scotopic ERGs were always significantly (
P < 0.05; compare mixed rod-cone b-wave and cone b-wave measurements at
Table 1 ) more attenuated than photopic ERGs, suggesting that rods are significantly more susceptible to bright-light insult and that this retinopathy mostly (or initially) affects rod function.