On microscopic examination, the normal, cuboidal cells of the RPE had changed to somewhat flattened, more heavily pigmented cells. These cells infiltrated and replaced the overlying retina and infiltrated and distorted the optic nerve anterior to the lamina cribrosa. The cells also invaded the choroid adjacent to the optic nerve (Figure 5). The tumor consisted of numerous, branching tubes lined by retinal pigment epithelial cells with large, ovoid melanin granules. In many areas, the tubular structures were well formed, while in other areas the proliferating cells had the appearance of linear strands, focal accumulations, and independent cells embedded in an eosinophilic stroma (Figure 6). These proliferating retinal pigment epithelial cells elaborated periodic acid–Schiff–positive material (Figure 5). The lamina cribrosa was undisturbed and the retrolaminar optic nerve was somewhat atrophic and gliotic. Embedded deep within the mass, but anterior to the lamina cribrosa, were fairly large, nonlaminated calcium deposits (Figure 5). Tumor cells extended from the main mass into the choroid and overlying retina without extraretinal extension. The tumor was not particularly rich in vascular channels and the vessels of the involved portion of the optic nerve and retina appeared normal. Bleached sections revealed minimal nuclear pleomorphism and an occasional nucleolus. The tumor was diagnosed histopathologically as an RPE adenoma involving the choroid, optic nerve anterior to the lamina cribrosa, and overlying retina with focal calcific degeneration.