Internal structure consistent with remodelling in very small drusen, revealed by filipin histochemistry for esterified cholesterol

Background/aims Drusen, the pathognomonic lesion of age-related macular degeneration, are dynamic and undergo both growth and regression. Using histochemistry to localise esterified cholesterol (EC), we investigated small drusen to discover signs of dynamism. Methods Flat mounts of Bruch's membrane were prepared from peripheral retinas of six donor eyes without chorioretinal pathology that were preserved within 6 h of death. Tissues were pretreated with ethanol to extract native unesterified cholesterol, incubated with cholesterol esterase and stained with filipin to bind unesterified cholesterol that was newly released by hydrolysis. Tissues were imaged with widefield epifluorescence microscopy. Diameters were measured and internal substructures (shells, lakes) assessed using previous descriptors. Results Of 676 drusen with mean diameter of 26.87 mm, 41.6% were stained homogeneously and 45.7% had lakes of pooled EC. Clusters of 2-7 drusen with similar staining patterns accounted for 25.3% of drusen. Increased EC content near the druse rim (shells) occurred in 10.5%. Conclusions Over half of very small drusen at the edge of clinical detectability have evidence for internal remodelling, suggesting that both formative and removal events are present early in the druse lifecycle.