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Anna Polosa, Pierre Lachapelle; Evidence Suggesting Retinotopic and Age Variability in Rate of Photoreceptor Loss Following Bright Light Exposure in Neonatal Rats. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5076.
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© ARVO (1962-2015); The Authors (2016-present)
Neonatal rats exposed to bright light develop a retinopathy (Light-Induced Retinopathy; LIR) where a specific region of the superior retina rapidly becomes photoreceptor-depleted, thus forming a retinal-hole-like (punched out) area that continues to grow long after the cessation of light exposure (Polosa et al., ARVO 2011). We aimed at determining if this gradual expansion of the retinal hole resulted from the normal aging process or if it reflected the slow degenerative process initially triggered by the light exposure.
Juvenile albino Sprague Dawley rats (n=65) were exposed to a bright cyclic light (10klux) from P14-28. Structural (histology) and functional (mfERG) analyses were performed at selected postnatal days that were regrouped as follows: Early Phase (EP: postnatal P30-P50), Intermediate Phase (IP: P55-P120) and Late Phase (LP: P400). Four predetermined retinal regions were analyzed: [Superior retina]: SR1 (300um from the optic nerve head), SR2 (1000um from ONH), SR3 (within 1300um from Ora serrata); [Inferior retina]: IR (1000um from ONH).
In controls, a gradual thinning of the Outer Nuclear Layer (ONL) was noted as the rat aged, with no evidence of hemiretinal difference. In LIR rats, EP showed a control-like rate of ONL loss in SR2 [decrease of 12±3% vs 13±3%, p>.05], while significantly faster rates of photoreceptor losses were measured for the other retinal locations [decrease of 19 ±1% SR1; 19±2% SR3; 17±2% IR; p<.01]. During IP, a significantly slower rate was measured in SR3 [decrease of 5±1% vs 13±2% in SR2, p<.001], while SR1, SR2 and IR followed a control-like rate. Finally, in LP, IR and SR1 showed the highest rate of ONL loss [decrease by 29±2% IR, 27±9% SR1 vs 14±4% SR2 p<.001]. Hence, by P400, SR3 stood out as the most resistant retinal area [ONL: 16±7% of control]; a finding also confirmed with mfERG.
Our results demonstrate that the rate of photoreceptor loss, that is triggered following bright light exposure of the neonatal rats, varies according to: 1-The stage reached by the pathophysiological degenerative process at the time when the measurements are taken and, 2-where on the retina (retinotopy) those measurements are taken (structure and function). These findings are reminiscent of how some forms of Retinitis Pigmentosa were shown to progress, especially at visual fields and symptoms.
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