Optic nerve drusens are cellular accretions of hyaline-like material in the optic disk. They are bilateral in 73% and frequently calcify. Many are asymptomatic, but arcuate visual field defects may be present. CT scan shows discrete rounded high densities confined to the optic disk surface. Choroidal osteomas can be idiopathic or may develop within a degenerated choroidal hemangioma or an inflammatory scar. They are usually located near the optic disk. If they involve the area of the fovea, vision will be affected. Colobomas are caused by a congenital defect in the sclera, allowing ocular contents to herniate posteriorly into the retrobulbar space. The optic nerve head is often involved by congenital colobomas. Staphylomas are caused by a weakened sclera due to infection, inflammation, glaucoma, or trauma, resulting in elongation of the globe and severe myopia.
near the anus. The most frequent cancerous tumor associated