Glaucoma is a complicated eye disease where damage to the optic nerve, leads to permanent vision loss. The optic nerve is responsible for carrying information from your eyes to the visual center in your brain.

Damage to the optic nerve can be caused by higher-than-normal inner eye pressure (also called intraocular pressure, or IOP). The pressure in one’s eye is a balance between the production of fluid within the eye and the drainage of the fluid out of the eye. Sometimes, however, glaucoma can happen when intraocular pressures are in a normal range. This is referred to as normal-tension glaucoma.

The most common type of glaucoma is called primary open-angle glaucoma (POAG). POAG causes gradual loss in peripheral vision. If not controlled or properly treated, it can progress to tunnel vision and ultimately lead to blindness.

Another type of glaucoma, though less common, is called angle-closure glaucoma. This type is also referred to as narrow-angle glaucoma as the structure responsible for drainage in the front part of the eye is too small, damaged, or partially closed. In some cases, this change in pressure can cause sudden symptoms such as eye pain, headache, halos, dilated pupils, vision loss, nausea, and vomiting.

References
Berdhal, J. (2019). Glaucoma: symptoms, treatment and prevention. All About Vision. Retrieved December 13, 2019, from http://allaboutvision.com/conditions/glaucoma.htm
Glaucoma: the silent thief of sight. Retrieved December 13, 2019, from http://mabeeeyeclinic.com/eye-heath-and-disease/glaucoma-the-thief-of-sight