Glaucoma is group of disease in which pressure is increased and it damages the optic nerve behind permanently.

The increased pressure, called intraocular pressure, can damage the optic nerve, which transmits images to the brain. If damage to the optic nerve from high eye pressure continues, glaucoma will cause permanent loss of vision. Without treatment, glaucoma can cause total permanent blindness within a few years.

https://en.wikipedia.org/wiki/Glaucoma