The definition of glaucoma is that the optic nerve in the back of the eye has been damaged. The cause of glaucoma is multifactorial. Elevated eye pressure has been the classic method that doctors have believed to be the cause of glaucoma. The damage to the optic nerve is felt to be due to decreased blood flow through the nerve head of the optic nerve. This diminished blood flow is usually felt to be due to elevated intraocular pressure. Genetic causes and cardiovascular disease can also contribute to it.
If you think of the eye being like a balloon, the tighter the balloon the more difficult it is to blow more air into it. The increase of pressure inside the eye diminishes the blood flow inside the eye. The decrease in blood flow decreases the amount of oxygen supplied to the eye.
Types of Glaucoma
There are two major types of glaucoma based on the anatomy or structure of the eye. The fluid that fills up the front portion inside the eye is called the aqueous humor and is produced by the ciliary body located behind the iris (colored portion of the eye). The fluid flows through the pupil and drains from the eye in the angle where the iris, cornea (front clear portion of the eye), and sclera (white portion of the eye). The fluid flows through the trabecular meshwork (cheesecloth like structure) and into a vein leading from the eye.
Narrow Angle or Acute Angle Closure Glaucoma
The angle between the iris and the cornea is too narrow. If the iris moves forward up to the cornea, the outflow is totally blocked which leads to a sudden elevation of the intraocular pressure. The pressure can rise to a very high level and cause permanent loss of vision or blindness. The eye becomes very painful, with blurred vision, loss of vision, nausea, and vomiting. This is an ocular emergency and a laser iridotomy needs to be performed to relieve the block and lower the eye pressure. Acute angle closure glaucoma comprises around 3 % of glaucoma.
Open Angle Glaucoma
The angle between the iris and the cornea is open. The obstruction to the flow of fluid out of the eye is in the trabecular meshwork. The pressure rise is slower and usually does not reach the high levels compared to angle closure glaucoma. Open angle glaucoma causes no symptoms in most cases. It slowly causes damage to the optic nerve over months to years and very slowly causes loss of peripheral vision. The loss of vision is so slow that people don’t realize that it is occurring. The treatment for open angle glaucoma consists of topical ocular medications, selective laser trabeculoplasty, and surgery. Most patients respond to the topical medications or selective laser trabeculoplasty. In severe cases where the eye pressure cannot be controlled a surgical procedure may be necessary.
Approximately 1 to 2 percent of Americans have glaucoma. The incidence in the African-American population is 6 to 7 times higher. Almost all patients who have glaucoma will be able to keep their vision. It is imperative that you keep your appointments and follow the directions of your eye doctor. If you have a family history of glaucoma, you should have your eyes checked on an annual basis after age forty. Remember that in almost all cases glaucoma does not cause any symptoms.