In vivo technique for autofluorescent lipopigments.

The content of the lipofuscin granule IS widely understood as the accumulated undigested consequence of prior oxidatrve damage to lipids and proteins (1,2). Oxidative damage IS of particular concern m the eye, because the photoreceptors function m an environment of high tissue oxygen, photosensitlzers (rhodopsm), and sunlight. The photosensitrve outer segments of the photoreceptors are particularly vulnerable because they contain both the highest concentratron of photosensitizer in the body, and the highest concentration of the easily oxidized polyunsaturated fatty acids. These highly fragile tissues are rapidly replaced; a new outer segment is generated approx every lo-12 d by addition of new material from the proxrmal side. The consequent constant elongation IS balanced by the daily removal of the distal tips by the RPE cells). These tips are ingested, rapidly digested, and cleared from the system. However, prior oxidative damage slows the digestive process, and undigested outer segment byproducts build up m the lysosomes of the RPE cells. These accumulations, called lipofuscm, increase over time; in an aging cell they may account for up to 25% of the cytoplasmic volume not occupied by mitochondrla or the nucleus (3).