Glaucoma is a group of eye conditions caused by a build-up of fluid inside the eye. In a healthy eye, fluid is produced and drains away through a fine meshwork, keeping the pressure steady.
If the fluid cannot drain properly, the pressure inside the eye rises. Over time, this raised pressure can damage the optic nerve — the bundle of fibres that carries visual signals from the eye to the brain.
Glaucoma is diagnosed when there is evidence of optic nerve damage caused by this raised pressure.