Quick-Freeze/Deep-Etch Visualization of Age-Related Lipid Accumulation in Bruch’s Membrane

Abstract

PURPOSE: To examine age-related changes in the ultrastructure of Bruch's membrane with quick-freeze/deep-etch (QFDE) and conventional thin-section transmission electron microscopy (TEM). METHODS: Four eyes from human donors aged 27, 41, 76, and 78 years were preserved within 4 hours of death. Full-thickness tissue blocks from the macula were prepared for TEM or for QFDE. RESULTS: Ultrastructure seen by conventional TEM was revealed in greater detail by QFDE. Cholesterol-containing particles (mean diameter, 80 nm) formed a thin densely packed layer external to the basal lamina of the retinal pigment epithelium (RPE) only in older eyes. The mesh size of the RPE basal lamina was smaller than the particles, and it appeared larger in older eyes. QFDE also revealed less decorated collagen fibrils in older eyes. CONCLUSIONS: The data suggest that the predilection of a extremely thin sublayer of inner Bruch's membrane for accumulating lipid particles may eventually lead to a confluent lipid wall capable of isolating the retina from its blood supply. If these lipids originate in the retinal pigment epithelium, then they are unlikely to have passed through the basal lamina in this form. The age-related increase in lipid particles corresponds with an age-related increase in hydraulic resistance determined in excised Bruch's membrane/choroid by others. QFDE will be useful for future modeling studies of Bruch's membrane transport and to identify those moieties responsible for deleterious age-related transport changes in Bruch's membrane.