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Anna Polosa, Pierre Lachapelle; Preventing AMD: Trust Your Genes More Than Your Pigmentation. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5688.
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There is still some controversies in the literature as to whether or not iris and ocular pigmentation may prevent (or retard) the occurrence of Age-Related Macular Degeneration (AMD). Supportive of the latter claim are results of ours presented at ARVO 2010 showing that pigmented rats were significantly more resistant to bright light exposure (a suggested animal model of AMD) compared to albino rats. We set to confirm our findings with different strains of albino and pigmented rats subjected to bright light exposure.
Adult albino [Sprague Dawley (SD; n=13) and Lewis (LW; n=4)] and pigmented [Long Evans (LE; n=9) and Brown Norway (BN; n=9)] rats were exposed to a bright cyclic light (10klux) for 6 consecutive days. Scotopic (-6.3 to 0.6 log cd.sec.m-2) and photopic (0.9 log cd.sec.m-2; background: 30 cd.m-2) ERGs and retinal histology were performed at days (D) 1, 15 and 30 post light exposure.
At D1, ERGs were similar in all the exposed groups with no recordable a-wave and a residual scotopic b-wave [SD-LW-BN: 6% and LE: 11% of control (p<.05)]. Over time (D30), a transient recovery was noticed only in the LW and LE groups [b-wave: 19% and 46% of control amplitude respectively (p SD: 87% > LE: 57% > LW: 27% of total SR]. The retina outside of the latter, highly damaged, area was best preserved in LE rats.
Our results show that the strain most vulnerable to LIR is the BN rat while the LE rat is most resistant; the difference in LIR expression between the two pigmented strains being highly significant. In contrast, the difference in LIR severity between the two albino strains was less pronounced. Our findings thus suggest that pigmentation alone cannot explain LIR resistance. Of interest, the most affected strain (BN rats) started (in control rats) with the longest photoreceptor outer segments, the highest count of photoreceptors, the thickest retina and the largest ERG. Clearly, other factors such as strain differences in intrinsic properties of the photoreceptors (especially rods), other biomolecular factors and genetics must be taken in consideration in order to explain the above differences. Funded NSERC and Réseau Vision.
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