Evidence against melanin as the mediator of retinal phototoxicity by short-wavelength light.
Albino and pigmented (black-hooded) rats of the Sprague-Dawley and Long Evans strains, respectively, were compared in terms of their susceptibility to retinal damage by ultraviolet-A light. Anesthetized animals were exposed to ultraviolet-A light (lambda max = 360 nm) for 4 hr and retinal damage was assessed 1 week later by electroretinographic analysis and measurement of outer nuclear layer thickness. Albino and pigmented animals showed approximately the same severity of ultraviolet-A retinal damage as a function of exposure irradiance. Furthermore, both pigmentation strains showed swelling and vesiculation of rod inner segment mitochondria as an early manifestation of damage. An abbreviated study on a congenic rat strain (F344-c/+) of albino and pigmented littermates again demonstrated an equal susceptibility to ultraviolet-A phototoxicity for both pigmentation phenotypes. These findings provide evidence that melanin is not the mediator of short-wavelength phototoxicity to the retina, since damage readily occurred in albino animals completely lacking this chromophore.
Rapp
L M
LM
Cullen Eye Institute, Baylor College of Medicine, Houston, TX 77030.
Smith
S C
SC
D016117:Albinism, Ocular; D000818:Animals; D004596:Electroretinography; D005260:Female; D008543:Melanins / Q000502:physiology*; D008854:Microscopy, Electron; D010786:Photoreceptor Cells / Q000648:ultrastructure; D010857:Pigment Epithelium of Eye / Q000473:pathology; D011833:Radiation Injuries, Experimental / Q000209:etiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012160:Retina / Q000473:pathology / Q000528:radiation effects*; D014466:Ultraviolet Rays / Q000009:adverse effects*
D008543:Melanins