There are two types of glaucoma:
Primary open angle glaucoma and closed angle glaucoma.
In open angle glaucoma, fluid builds up gradually within the eye and leads to eventual optic nerve damage. It is painless and in the initial stages, causes no damage at all.
Closed angle glaucoma occurs when the iris is too close to the drainage angle and blocks fluid from moving out of the eye. This causes the fluid to build and create high pressure that damages the optic nerve.
Contrarily, closed angle glaucoma develops slowly, as in, the movement of the iris close enough to the drainage angle to block does is slow. However, once the drainage angle is blocked, the problem accelerates very quickly.
Closed angle glaucoma is fast acting and can cause blindness if not treated as an emergency.
If not treated timely, both types of glaucoma cause irreversible blindness.