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Sachiko Kaidzu, Tsutomu Okuno, Masaki Tanito, Akihiro Ohira; Retinal Light Damage Induced by Light Exposure at Different Intervals in Rats. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5355.
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We tested the retinal damage induced by twice light exposure with different interval in rats.
Under deep anesthesia, the left eyes of 5-week-old Sprague-Dawley albino rats (n=6 for each condition) were exposed to narrow-band light with 20 nm in bandwidth at wavelength of 420 nm, using a xenon lamp source with a bandpass filter (Asahi Spectra Co., Ltd., Tokyo, Japan). The right eyes, left unexposed to light, served as controls. Total dose of 170 J/cm2 or 340 J/cm2 (retinal radiant exposure) was exposed at once or at twice with different exposure intervals (1, 2, 4 or 8 days). The retinal radiant exposure was determined by multiplying the measured corneal radiant exposure by the combined transmittance of the rat lens and cornea. Three weeks after the exposure, flash electroretinograms (ERGs) were recorded. Both eyes were enucleated and retinal sections containing the whole retina including the optic disc were stained with hematoxylin-eosin (H & E) and outer nuclear layer (ONL) thickness was measured.
Compared to unexposed eyes, significant reductions in a- and b-wave ERG amplitudes and in ONL thickness were observed for all exposed eyes. However, in the eyes exposed to 170 J/cm2, the damage induced by twice light exposure (85 J/cm2 x 2) was less severe than that induced by single exposure (170 J/cm2 x 1). Among the intervals, 8-day interval reduced the damage most remarkably. In the eyes exposed to 340 J/cm2, there was the tendency that the damage induced by twice exposure was reduced compared with that induced by single exposure, but difference didn’t reach statistically significance.
By low dose exposure (170 J/cm2), the retinal damage induced by twice exposure was reduced compared with that induced by single exposure; longer interval reduced the damage more effectively. "Preconditioning" effect by initial exposure may explain the retinal resistance induced by twice light exposure regimen.
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