High-resolution histologic analysis of the human choroidal vasculature

Purpose. To develop a high-resolution histologic technique to study the postmortem human choroidal vasculature in dual perspective: vascular pattern in the flat perspective and structure in cross sections. Methods. Fresh whole human choroids were denuded of retinal pigment epithelium, fixed, incubated for enzyme histochemical demonstration of alkaline phosphatase (APase) activity, bleached with hydrogen peroxide, and flat-embedded in glycol methacrylate. Vascular patterns were examined and documented en bloc, and subsequent serial sectioning was performed through specific sites of interest. Results. APase staining provided excellent visualization of the entire choroidal vasculature en bloc. Reaction product was generally more prominent in the choriocapillaris and collecting venules than in veins or arterioles, whereas arteries had the least activity. Diminished activity within focal regions of the choriocapillaris was observed in the far periphery of most aged subjects and was related to loss of endothelium and capillary atrophy. Hard drusen were generally observed in clusters located near collecting venules and appeared unrelated to any underlying angiopathy, whereas basal linear and laminar deposits were most often associated with regions of capillary dropout. Choroids from patients with diabetes demonstrated angiopathic changes consisting of extensive capillary dropout, beaded capillaries, neovascularization, and Bruch's membrane degeneration. Conclusions. The benefits afforded by this method of analysis are that choroidal vasculature can be visualized in the native state and that nonvascular structures are retained for simultaneous analysis with vascular pattern and blood vessel structure.