The Effect of Pupil Size in Light-induced Retinopathy (LIR) of Long Evans (LE) Rats

Abstract

Purpose: : At last year’s ARVO we presented results suggesting that bright light exposure could be beneficial to the retinal structure and function of the developing pigmented LE rat. We examined if the lack of pupil dilation could have explained this unexpected result.

Methods: : LE rats were exposed [with (DP) and without (NDP) pupil dilation (n=4 per group)] to a bright cyclic (12D:12L) light of 10 000 lux between P14-P28 (Juvenile) or for 6 consecutive days (adult) respectively. Outcome measures (obtained at P30 and P60) included scotopic (intensity: -6.3 to 0.6 log cd.sec.m-2; 12 hrs dark adaptation) and photopic (intensity: 0.9 log cd.m-2.sec; background: 30 cd.m-2) ERGs and histology.

Results: : In adult DP rats, light exposure significantly (p.05) increase in amplitude of all ERG components (except the rod Vmax) and a significant (p<.01) increase in thickness of the OS (32%) and ONL (25%). In juvenile DP rats at P30, light exposure significantly decreased (p<.001) the amplitude of the mixed a-wave (45%), mixed b-wave (23%) and cone b-wave (22%). Histology also revealed a thinning of the ONL and OPL by 33% (p.05) increase in thickness of the outer segment (OS: 14%), ONL (3%) and IPL (14%) was observed in the NDP rats at P30 and P60.

Conclusions: : Although in adult, and to a lesser extent in juvenile LE rats, pupil dilation does generate a more potent LIR, the enhancement in structure and function observed in the adult and juvenile NDP retina along with the near complete recovery of retinal structure and function at P60 in the juvenile DP retina suggest that pigmentation and/or pupil dilation would make a difference. The retinal mechanisms at the origin of this neuroprotective effect remain however to be elucidated.

Keywords: electroretinography: non-clinical • radiation damage: light/UV • photoreceptors