Glaucoma develops when fluid pressure within the eye reaches a level that is too high for the health of the optic nerve. The optic nerve is similar to an "electrical cable" that carries light impulses from the eye to the brain. Abnormal fluid pressure damages the nerve fiber layer and blood vessels in the optic nerve and, as a result, vision can become impaired.
Glaucoma can be separated into two broad categories, Open Angle and Angle Closure (narrow angle) Glaucoma. Open Angle Glaucoma, the more common condition, occurs when the internal glaucoma drain of the eye (trabecular meshwork) does not function properly and the fluid pressure builds up within the eye. Open Angle Glaucoma tends to develop slowly and may have no symptoms until some vision has been permanently lost.
In Angle Closure or Narrow Angle Glaucoma, the iris physically obstructs the internal drain of the eye. The glaucoma drainage inlet becomes narrow due to the position of the iris such that trabecular meshwork is not visible upon examination. This type of glaucoma can develop suddenly with an abrupt closure of the drainage inlet. Emergency treatment may be required for this acute and often painful condition.