Pathologic features of senile macular degeneration.

Senile macular degeneration (SMD) has several morphologic forms that may exist singly or in various combinations. Patients with drusen are at an increased risk to develop SMD. Types of drusen that have been recognized clinically and histopathologically include hard or nodular, soft, glistening or calcified, and diffuse. Hard drusen are probably a consequence of extrusion of material from one or a cluster of retinal pigment epithelial (RPE) cells. Soft drusen are a sign of more widespread disease of the RPE, develop in eyes with hard drusen, and represent small areas of serous detachment of the RPE and the thickened inner aspect of Bruch's membrane. RPE areolar atrophy can occur in the setting of hard and soft drusen and in larger RPE detachments. From the morphologic point of view, we propose that the process leading to disciform scar formation in SMD begins with thickening of the inner aspect of Bruch's membrane due to production of abnormal basement membrane by the RPE. This thickened area is weakly attached and allows the development of localized detachments (soft drusen). These localized detachments become confluent into large detachments of the RPE. Choroidal neovascularization occurs in association with diffuse and soft drusen and larger serous RPE detachments. Bleeding from neovascular tissue leads to disciform scar formation.