Surprise mechanism behind light-induced blindness

It has been known for decades that exposure of mammals to constant light for many weeks, even at low or moderate levels, results in severe retinal degeneration and visual impairment. The basis for this light-induced damage has remained poorly understood, but this week researchers report findings that run counter to the anticipated connection between light-induced retinal degeneration and accompanying blindness.

To characterize the mechanism of photoxicity due to constant light, researchers at the Johns Hopkins University School of Medicine studied this phenomenon in the fruit fly, Drosophila melanogaster. The researchers, Drs. Seung-Jae Lee and Craig Montell, found that the visual impairment caused by constant light occurred through a mechanism separate from that which underlies the light-induced retinal degeneration. Moreover, these workers found that the light-induced blindness resulted from a gradual decline in the concentration of the light-receptor, referred to as rhodopsin. Manipulations that decreased the rate of light-induced loss of rhodopsin greatly decreased the visual deficit resulting from constant light. The study raises the possibility that drugs that inhibit degradation of rhodopsin may reduce the severity of visual impairment that results from long-term exposure to moderate or even low levels of light.

Seung-Jae Lee and Craig Montell: "Visual Impairment from Continuous Illumination Occurs through an Arrestin-Dependent Pathway that Promotes Degradation of Rhodopsin"

Publishing in Current Biology, Volume 14, Number 23, December 14, 2004, pages 2076–2085. http://www.current-biology.com

This work was supported by a grant to C.M. from the National Eye Institute (EY08117).

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