Figure 4. Semithin sections of the eye shown in Figure 2J,K. A: The endothelial cell layer of the choriocapillaris was irregular, and endothelial cells protruded into the vessel lumen (black arrowheads). Evidence for this is presented by electron microscopy (see Figure 5A-C). The retinal pigment epithelium (RPE) cell layer was disrupted (white arrowheads), and endothelial cells migrated and proliferated into the subretinal space or between Bruch’s membrane and RPE (inset). Evidence that these cells were endothelial cells is presented by immunohistochemistry (see Figure 6A). These cellular proliferations were either solid (white asterisk in A) or loosely packed with interstitial spaces (black asterisk in B). The photoreceptors have already degenerated, and retinal scar was closely connected to the RPE and proliferating cells. This was probably why fluorescein leakage was restricted to the spotted roundish areas visible in Figure 2. An immature capillary containing an erythrocyte was located distally to the RPE (B, white arrow). The melanocytes of the choroids were located below the deeper choroidal vessels and are not shown. C and D: After injection of HC Ad. EGFP or PBS, the RPE, choriocapillaris (arrowheads) and deeper choroidal vessels (arrow) appeared to be normal. The pigmented layer, consisting predominately of melanocytes, is marked by a black asterisk. The double arrows in A-C indicate growth of extracellular matrix and vessel layers of the choroid after VEGF expression (A, B) compared to (C).