Glaucoma Causes

In addition to advanced age, a number of factors are associated with the development of glaucoma. These include:

Elevated IOP levels

Each day, the eye produces about 1 tsp of aqueous humor—a clear fluid that provides nutrients to and carries waste products away from the lens and cornea. (In other parts of the body, the blood carries out these functions, but the lens and cornea have no blood supply.) The aqueous humor is produced by the ciliary body, which surrounds the lens. Aqueous humor flows from behind the iris, through the pupil, and into the front chamber of the eye. It then drains from the eye through a spongy network of connective tissue called the trabecular meshwork, where it ultimately enters the bloodstream.

An alternate drainage system, known as the uveoscleral pathway, is located behind the trabecular meshwork. Ordinarily, fluid production and drainage are in balance, and IOP remains between 12 mm Hg (millimeters of mercury, the same units of measurement used for blood pressure) and 20 mm Hg.

However, when too little fluid is drained, IOP becomes elevated, eventually causing damage to the optic nerve in some people. In people with open-angle glaucoma who have higher-than-normal IOP levels, ophthalmologists suspect that a partial blockage of the trabecular meshwork traps the aqueous humor. Exactly how this happens is unclear. As more aqueous humor is produced than is removed, the blockage causes IOP to rise. Initially, IOP does not rise high enough to cause discomfort or any easily perceived changes in vision, but when it remains elevated or continues to rise, fibers in the optic nerve are compressed and eventually die, leading to a gradual loss of vision over several years.

Closed-angle glaucoma results when aqueous humor is blocked at the pupil, leading to a bowing forward of the iris that stops aqueous humor from reaching the trabecular meshwork. The blockage causes a sudden increase in IOP that can lead to optic nerve damage, resulting in severe, permanent vision damage within just one to two days if not treated immediately.

Thin corneas

In some individuals, a normal level of IOP does not preclude optic nerve damage. Thinner-than-normal corneas can make IOP measurements appear to be lower than they actually are. Thin corneas may therefore be a risk factor for glaucoma. The American Academy of Ophthalmology now recommends that people with other risk factors for glaucoma (for example, advanced age, elevated IOP, and black ancestry) have their corneal thickness measured. It often takes several measurements of IOP over an interval of months to obtain an accurate reading.

Heredity/genetics

Close relatives (mother, father, brother, sister, biological children) of those with open-angle glaucoma have a much greater chance of developing the disease than those who don’t have a close relative with the condition. It is vital for these individuals, once the relative has a diagnosis of glaucoma, to undergo annual detailed eye exams that include a dilated pupil examination of the optic nerve and a visual field test.

Defects in several genes are now thought to be associated with the development of glaucoma in some people who have the condition. As of January 2016, 15 genes that contribute to the condition had been identified. For example, defects in the optineurin gene have been seen in people whose open-angle glaucoma occurs at lower IOPs. The role of optineurin is not well understood.

Myocilin plays a part in how the eye allows aqueous humor to flow out of the trabecular meshwork. People with mutations in this gene develop high IOP at an early age as a result of interference with the outflow of aqueous humor by the interaction of the mutant molecule and the normal components of the trabecular area.

Researchers have also recently discovered that, when overactive, a gene known as secreted frizzle-related protein 1 (sFRP1) increases IOP. In addition, sFRP1 is much more likely to be overactive in people with glaucoma.

Scandinavian researchers have discovered two mutant forms of a gene called lysyl oxidase-like (LOXL1) that are responsible for 99 percent of exfoliation glaucoma cases. Exfoliation glaucoma occurs when fibers of connective tissue within the eye break off and accumulate in the lens.

Steroid use

Inhaled and nasally administered drugs that contain corticosteroids, commonly used to treat asthma and allergies, may increase the risk of elevated IOP and open-angle glaucoma, possibly by interfering with the drainage of aqueous humor. Oral corticosteroids may have the same effect. If you must use corticosteroids, have your IOP monitored regularly.

Updated by Remedy Health Media

Publication Review By: Susan B. Bressler, M.D., Harry A. Quigley, M.D., Oliver D. Schein, M.D., M.P.H.

Published: 28 Feb 2011

Last Modified: 29 Jan 2016