Choroidal Blood Vessels Are Protected from Light Toxicity by Melanin Pigmentation

Abstract

Abstract: : Purpose: Humans with dark fundus pigmentation (black Africans) have much less prevelance of disciform macular degeneration than white Caucasian with blue iris (BR.J OPHTALMOL.1978, 62:547-50). Therefore we compared cell damage in retinal and choroidal tissues of pigmented (Long Evans) and Albino (Wistar) rats after exposure to visible light. Methods: The pupils of albino and pigmented rats were dilated with phenylephrin-trocamid to avoid light absorbance by the iris pigmentation. Each rat was exposed to visible light for 30 minutes. As light source we used the lamp LK 1500 LCD / Shott Glas- Fiber Optics Division - Germany ) with the light guides. The distance from the light guides was only 5 mm ( 140.000Lux ) at the surface of cornea. Following exposure to light, animals were sacrificed after 22 hours. Eyes were enucleated, the anterior segment was cut off at the equator, fixed and embedded for light / electron microscopy. Morphometric analysis was performed using a zeiss axioplan light microscope connected to a personal computer equiped with a video camera module. Results: Under our experimental conditions of illumination, damage appeared to affect RPE, ROS, and photoreceptor cells of both animal strains The mean value of photoreceptor cell nuclei height in LE rats was 31.6 + 7.2 µm and that of Wistar rats was 18.2 + 18.8 µm ( n = 12 ; student's t-test, p< 0.02). The mean value of the lenght of ROS in LE was 26.6+5.6 and that of Wistar 10.5 +12.4 ( n = 12 ; p< 0.0004 ). The mean value of intact RPE - lenght in % of LE was 100 % and that of Wistar rats was 52,8 % +38.7 ( p<0.0003 ). The number of obstructed choriocapillaries / 0.5 mm sectioned choroid in LE was 0.7+1 and in Wistar rats was 3.4+1.9 ( n=12 p<0.0004 ) Conclusions: Our study show a great difference in the cell damage level between albino and pigmented rats. For the first time we show that choroiocapillaris can be damaged by light toxicity. The results show that melanin pigmentation is important for protection of retinal and choroidal tissues by light toxicity and may play a role in serious diseases like aged macular degeneration ( AMD ).

Keywords: retina • retinal pigment epithelium • age-related macular degeneration