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J. Racine, S. Joly, S. Chemtob, P. Lachapelle; Light–Induced Retinopathy (LIR): Comparing Guinea Pigs and Rats . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3082.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies of ours showed that albino rats exposed to a bright luminous environment (10 000 lux) for 6 consecutive days developed a severe LIR with near complete abolition of retinal function. Rods being first (and most) affected led some to suggest that LIR was rhodopsin mediated. The functional anomalies were also accompanied by 1– the destruction [most pronounced in the superior retinal hemisphere (SRH)] of the photoreceptor layer (PL) and 2– a remnant ONL. The purpose of this study was to determine if a LIR of this magnitude could also be evidenced in another albino model namely: the guinea pig (GP).
Albino GP were maintained under bright cyclic light (10 000 lux; 12D:12L) from P15 to P30. Scotopic ERG luminance–response functions (intensities: –6.3 to 0.9 log cd.m–2.sec) and photopic ERG (0.9 log cd.m–2.sec; background: 30 cd.m–2) were obtained after 5 (L5), 10 (L10) and 15 (L15) days of light exposure. The retinas were harvested for histology following a 15–day period of light exposure.
In GP, most of the functional changes appeared after 15 days of exposure. PHOTOPIC ERG: Irrespective of the duration of the exposure, the amplitude of the a–wave along with the peak time of the b–wave remained unchanged (p>0.05). There was however a small but significant reduction in b–wave amplitude (control: 138.34 ± 4.06µV; exposed: 125.83 ± 7.26µV; p<0.05) along with a significant delay in the peak time of the a–wave (control: 12.80 ± 0.23ms; exposed: 13.73 ± 0.31ms; p<0.05). Of interest, the number of OP was reduced from 5 to 4. SCOTOPIC ERG: None of the scotopic ERG components were significantly altered following the 15–day exposure. Retinal histology revealed significant increases in the thickness of the ONL (control: 25.00 ± 1.2µm; exposed: 30.90 ± 2.16µm; p<0.05) and GCL (control: 12.50 ± 0.72µm; exposed: 17.94 ± 2.39µm; p<0.05) a feature that was most pronounced in SRH.
Albino GP do not generate a LIR nearly comparable to the devastating one previously demonstrated with the albino rats. Cones are most affected in GP while rods are in rats. Histology reveals massive destruction of the PL in rats and minimal pathology in GP. It is doubtful that the retinal difference in cone proportion (GP: 8–12%; rats: <2%) or level of retinal illumination can explain these differences. Our results thus suggest that 1–albino animals are not equally susceptible to the effect of a bright environment and 2–the claim that LIR is rhodopsin mediated may not be universal. Supported by CIHR and FRSQ vision network.
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