Glaucoma is an optic neuropathy characterized by apathological process called cupping, which is a type of opticatrophy .This produces nerve fiber layer defects that result invisual field defects. Glaucoma is often, but not always associatedwith elevated intraocular pressure " IOP".Ocular perfusion pressure is the difference between bloodpressure and IOP (blood pressure – IOP). Thus, a drop in theperfusion pressure can be caused by drop in the blood pressure orrise in the IOP.