Lipofuscin granules in human photoreceptor cells.

Twenty-four human retinas were structurally examined in order to study the degradative pathway in inner segment turnover. Lipofuscin granules were found in myoids of photoreceptor inner segments. Cone lipofuscin granules exhibited autofluorescence, in ultraviolet light. Both the cone lipofuscin granules (-1.6 micron) and the rod ones (-0.6 micron) were membrane-limited inclusions comprising different contents. Various vacuoles related to autophagy were found in the myoids of rods and cones. Acid phosphatase activity was demonstrated in lipofuscin granules of the rods and cones, as well as adjacent various vacuoles. A survey of the cone lipofuscin granules in the semithin Epon sections revealed that more than one-half of the eyes from humans over 30 years of age contained cone lipofuscin granules, whereas eyes from those under 30 years of age did not. These results strongly suggest that lipofuscin granules represent an accumulation of residual bodies of autophagy in the photoreceptor inner segments.