what is glaucoma? Is it common?

Glaucoma is actually a group of eye diseases that lead to damage of the optic nerve (the bundle of nerve fibers that carries information from the eye to the brain), which can then lead to vision loss and the possibility of blindness. Optic nerve damage usually occurs in the presence of high intraocular pressure; however, it can occur with normal or even below-normal eye pressure. Glaucoma is estimated to affect approximately three million Americans, and up to half of these individuals may be unaware that they have it.