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W. Liu, A. Polosa, P. Lachapelle; Dynamic of the Light-induced Retinopathy in Juvenile Albino Sprague Dawley Rats. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3610.
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Juvenile Sprague-Dawley (SD) rats exposed to a bright luminous environment after eye opening will develop a Light-Induced Retinopathy (LIR), the features of which will be most obvious when the rat reaches adulthood. The purpose of our study was to investigate the dynamic of LIR from juvenile age to adulthood.
Juvenile Sprague Dawley(SD) rats were exposed from P14 to P28 to a bright light (12D: 12L; 10 000 lux). Scotopic (intensity: 0.6 log cd.m-2.sec) and photopic (intensity: 0.9 log cd.m-2.sec; background: 30 cd.m-2) electroretinograms (ERG) and flash visual evoked potential (VEP) were recorded at regular intervals from P30 to P120 following which the eyes were prepared for histology.
At P30, the amplitude of mixed rod-cone a-wave of the exposed rats was significantly reduced to less than 10% of normal (28.48±4.87 µV; 321.15±27.68 µV; P<0.05). While in control, the a-wave gradually reached its lowest value at P60 (70% of P30), in exposed rats the a-wave doubled from P30 to P35 (P<0.05), increased again to P35 value at P55 and finally plunged and remained at P30 value from P60 on. A similar oscillatory pattern was observed for all ERG components. Likewise, at P30 and P45, the VEP was 15% smaller than control, 50% larger at P40 and 30% larger at P50. At P30, the outer segment layer (OSL) was 30% (P<0.05) of normal and remains such despite some outer segment regrowth seen between P30-40. A gradual loss in ONL thickness from 50% (P30) to 10% (P120) of control was also observed.
We believe that the initial increase in function between P30-P35 most probably results from a photostasis effect as evidenced with the slight regrowth of the OS. The transient nature of this phenomenon explains the drop in function observed at P45. The second wave of enhancement in function that peaks at P55 and its following drop could reflect a retarded maturational process (and accompanying apoptosis) that was delayed as a result of the bright light exposure period.
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