Although many cases of glaucoma are caused by high eye pressure, there are an increasing number of patients that develop damage to the optic nerve even with low eye pressures. Certainly, glaucoma is caused by high eye pressure, and also by other factors such as poor perfusion (i.e. blood supply) to the nerve. In other cases, glaucoma is caused by having a crowded drainage angle (narrow angle glaucoma).

There are many types of glaucoma; in most cases the exact cause of raised pressure is not identified infact. Sometimes glaucoma can be caused by injury to the eye, or by other eye conditions, or by the use of medications (e.g. steroids in just about any form). Generally, whatever the cause, glaucoma is treated similarly. Some types of glaucoma respond less well to medication, or less well to laser or surgery.

Visual field of a patient with glaucoma.