Glaucoma is a group of eye conditions that damage the optic nerve where it leaves the eye. The Optic Nerve carries information from the retina to the brain where it perceives it as a picture.
The eyeball is kept in shape by the pressure of fluid in the eye. Fluid is formed and flows into the eye and should equally drain out again keeping the fluid fresh. The eye pressure is largely independent of blood pressure.
If a blockage occurs in the drainage area and the fluid can not escape, the eye pressure will rise and this causes the optic nerve to come under too much pressure and be injured. The damage can depend on how high the pressure is, and how fast it rises. Low level of pressure causes damage to happen more slowly and is no pain. High pressure is very painful and causes rapid damage. Sight will be gradually lost, if you do not go for medical treatment.
As with all eye health situations and to get rapid treatment, it is important to visit your Optician regularly or if you have cause for concern.