Glaucoma is a group of eye diseases in which the optic nerve, which connects your eye to your brain, is damaged by the pressure of the fluid inside your eye.
This may be because the pressure is higher than normal, or because the nerve is more susceptible to damage from pressure. This may affect one or both of your eyes.
There are two main types of glaucoma: chronic glaucoma, which happens slowly and acute glaucoma which happens quickly. Chronic glaucoma is much more common than acute glaucoma.