Scanning electron microscopy of human drusen.

Drusen are small, yellowish deposits that form under the retinal pigment epithelium (RPE) with senescence or under certain pathological conditions. The present study examined these structures under the scanning electron microscope. Tissue came from four eyes of 66- and 75-year-old donors who demonstrated widespread drusen of the posterior fundus noted on postmortem examination. Specimens were prepared by either detaching the RPE from Bruch's membrane, or by cryofracturing the tissue for cross-sectional views. Drusen appeared to be composed of irregularly-shaped globular masses and of distinct spherical entities. These particles varied greatly in size, and were situated between the RPE's basement membrane and the outer collagenous zone of Bruch's membrane. Surface views showed drusen components to be embedded in the collagenous zone of Bruch's membrane. Pits corresponding to the sizes of the globular and spherical masses imply that some particles were lost during tissue processing. Fractured cross sections of the irregularly-shaped globular masses revealed a homogeneous, granular matrix with no distinct ultrastructural features, while some of the fractured spherical components demonstrated an internal core. Transmission electron microscopic analysis on the same specimens that were subjected to SEM corroborated these observations. Analytical x-ray microanalysis (Kevex, Foster City, CA) in the SEM revealed major peaks for calcium and phosphorous in the crystalline spherical components, and primarily potassium and chloride in the globular structures.