What is glaucoma?
Glaucoma is a condition (more accurately, a group of related conditions) where the optic nerve is slowly damaged. The optic nerve connects the eye to the brain and damage caused by glaucoma causes irreversible loss of sight.
The commonest form of glaucoma is called Primary Open Angle Glaucoma (POAG). Typically, POAG causes damage, which initially affects the peripheral vision which is not noticed by the patient. Without treatment, damage may continue slowly, eventually causing loss of central vision with blindness. The whole process from normal sight to blindness can take many years. High eye pressure is the commonest recognized cause of POAG, though about 30% of patients develop glaucoma despite apparently normal eye pressure (Normal Tension Glaucoma, NTG).
Because early glaucoma is symptomless it is usually noted as part of the routine examination undertaken by an optometrist (optician). The optometrist will identify glaucoma by measuring the eye pressure, examining the optic nerve and evaluating the field of vision.

Ms. Aoife Doyle | Consultant Ophthalmic Surgeon | M.B., M.Med.Sc, E.B.O.D, F.R.C.Ophth. (uk)