FUNCTION AND MORPHOLOGY OF THE RETINAL-PIGMENT EPITHELIUM AFTER LIGHT-INDUCED DAMAGE

The purpose of this study was to determine the threshold energy for li ght-induced functional damage of the retinal pigment epithelium at var ious wavelengths. Retinas of 58 pigmented and 21 albino rabbits were e xposed to low intensity broadband blue light (400-520 nm), yellow ligh t (510-740 nm), and narrowband blue light (408, 417, 439, 455, 485, 50 1 nm, respectively; Delta lambda = 10-13 nm. The intensity values were 50, 280, and 5 mW . cm(-2), respectively, and the illumination time w as 0.5 up to 5 h. The cumulative dose of light energy was calculated f rom these data (J . cm(-2)). The blood-retinal barrier dysfunction was evaluated in vivo using fluorophotometry to measure the leakage of fl uorescein into the vitreous after intravenous injection and in vitro u sing light and electron microscopy after an in vivo intraarterial inje ction of horseradish peroxidase (HRP). The threshold energy for fluore scein leakage was 50 J . cm(-2) for blue light and 1,600 J . cm(-2) fo r yellow light. After broadband blue light exposure, the HRP reaction product was seen in the cytoplasm of the retinal pigment epithelium (R PE) cells and in the subretinal space but only if fluorescein leakage had been observed. Threshold energy and fluorescein leakage as a funct ion of light energy were similar for albino and pigmented rabbits (P > 0.5). Only after yellow light exposure in excess of 3,700 J . cm(-2) was fluorescein leakage found. In that case complete disruption of the RPE was seen, but no HRP was observed in the RPE cytoplasm. Of the na rrow-band blue light exposures, only that at lambda = 418 nm caused a significant increase in fluorescein leakage; the threshold energy was 18 J . cm(-2). Blue light was found to be at least 30 times more effic ient than yellow light in causing dysfunction of the blood-retinal bar rier. The most efficient wavelength was 418 nm, corresponding with the absorption spectrum of cytochrome c oxidase. Melanin seemed to play n o role. The presence or absence of melanin in the RPE appeared to have no influence on the threshold energy. (C) 1997 Wiley-Liss, Inc.