Lipofuscin and macular degeneration.

The accumulation of the autofluorescent pigment lipofuscin in the retina that occurs with aging has been explained as a side effect of the visual cycle. It occurs when two molecules of all-trans-retinal condense with one molecule of phosphatidylethanolamine in the discs of the rod outer segments, and is followed by uptake into retinal pigment epithelium (RPE) and conversion to the stable A2E, a pyridinium bisretinoid that is toxic to RPE cells. The accumulation of A2E, the major component of lipofuscin causes RPE cell apoptosis, thereby explaining age-related macular degeneration and macular degeneration characteristic of Stargardt disease. The drug isotretinoin (13-cis-retinoic acid) prevents accumulation of A2E in mice by slowing down the visual cycle and might therefore be used to prevent macular degeneration.