Glaucoma is a group of afflictions that have loss of eyesight in common. This impairment of vision is caused by damage to the optic nerve as a result of high intraocular pressure. The patient’s optical fields narrow and at last only a tiny rest is left. The mechanisms of the disease are well known but it is in most cases unexplained why a person develops glaucoma. This review discusses the several forms of glaucoma, the diagnosis and therapy, and the epidemiology and prevention.