Excess fluid is drained via channels near the iris. Eye pressure becomes excessively high when too much fluid is produced, or the drainage canals become blocked. High eye pressure can physically compress the optic nerve or interrupt blood flow feeding the nerve. In either case, the end result is nerve damage. This causes vision loss.
Central vision is lost in severe glaucoma.
Diagnosing glaucoma is difficult because it takes several years for damage to be noticed even to the highly trained. However, there are exceptions depending on the type of glaucoma. Primary Open Angle Glaucoma , is the most common type. It is usually very slow in onset and progression. Traumatic Glaucoma occurs when and injury to the eye makes the optic nerve more susceptible to small changes in IOP, and alters the structure of the drainage system.