Basic mechanisms underlying the production of photochemical lesions in the mammalian retina.
Extended exposure (100s) of the macaque retina to blue light (400-500nm) produces a photochemical type or types of lesion. The basic mechanisms responsible for such photic damage are unknown but the toxic combination of light and oxygen leading to the free radicals O-.2, H2O2, OH., and O2(1 delta) have been suggested as a possible source of the phototoxicity. To test this hypothesis, the radiant exposure (J. cm-2) to short wavelength light (435-445nm) required for minimal damage in the macaque retina is under investigation as a function of oxygenation and after administration of substances known to either inhibit/scavenge radicals or act as anti-inflammatory/anti-oxidant agents. Substances under study include beta-carotene, steroids, catalase and SOD. Here we report radiant exposure in J.cm-2 needed to produce a minimal lesion vs oxygenation as measured by partial pressure of O2 in arterial blood (Po2). There is a sharp drop in the radiant exposure threshold with increase in the partial pressure of O2 in arterial blood, e.g. 30 J.cm-2 at 75 torr to 10 J.cm-2 at 271 torr, a factor of 3. Methylprednisolone injected intravenously one hour before exposure (125 mg) has been shown to raise the threshold for retinal damage in two macaques by a factor of approximately 2. Another animal fed beta-carotene (7.5 mg daily) over a period of 3 months has been exposed to blue light at several levels of oxygenation. The results suggest a protective effect.
D000818:Animals; D002338:Carotenoids / Q000494:pharmacology; D005609:Free Radicals; D008027:Light / Q000009:adverse effects; D008251:Macaca; D008775:Methylprednisolone / Q000494:pharmacology; D010100:Oxygen / Q000494:pharmacology / Q000528:radiation effects; D010777:Photochemistry; D012160:Retina / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D019207:beta Carotene
D005609:Free Radicals; D019207:beta Carotene; D002338:Carotenoids; D010100:Oxygen; D008775:Methylprednisolone