Drusenoid maculopathy in rhesus monkeys: autofluorescence, lipofuscin and drusen pathogenesis

To examine patterns of retinal pigment epithelial autofluorescence and lipofuscin accumulation in relation to drusen and to explore the pathogenesis of drusen in rhesus monkeys.

The macular areas of six rhesus monkeys, euthanized at 19 to 28 years of age, were studied by bright field and fluorescence light microscopy and transmission electron microscopy.

There was strong autofluorescence in the retinal epithelium that tended to diminish over drusen. Electron microscopy revealed that all retinal epithelial cells had large concentrations of lipofuscin bodies. The epithelial cells overlying drusen, however, tended to have less lipofuscin than epithelial cells not associated with drusen. Electron microscopy revealed that the epithelial cells overlying drusen were losing segments of cytoplasm containing lipofuscin bodies. Macrophage-like cells were consistently present in Bruch's membrane microns away from this lipofuscin-containing cytoplasmic material.

Retinal epithelial cells overlying drusen have less lipofuscin than neighboring epithelial cells. The loss of lipofuscin seems due to a loss of cytoplasm containing lipofuscin that contributes to drusen formation. Macrophages in Bruch's membrane may be responsible for removing this lipofuscin debris. The results support in vivo studies showing reduced autofluorescence over drusen and support the "budding" of epithelial cytoplasm as a source of drusen material.