Glaucoma is one of the most important causes of blindness worldwide. It is a complex disease typically characterized by increased IOP, damage to the optic nerve, and irreversible vision loss. 2. The pathogenesis of optic nerve damage in glaucoma is not fully understood. Ischemia may play a major role. Over time there is a loss of ganglion cells, leading to atrophy of the optic disc (and enlargement of the optic cup, called “cupping”).