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The mechanisms that cause glaucoma are not fully understood. In most cases, a painless elevation of IOP occurs, which can lead to progressive vision loss and optic nerve damage.

High pressure inside the eye is caused by an imbalance in the production and drainage of fluid in the eye (called aqueous humor). The channels (called trabecular meshwork) that normally drain the fluid from inside the eye do not function properly. More fluid is continually being produced but cannot be drained because of the improperly functioning drainage channels. This results in an increased amount of fluid inside the eye, thus raising the pressure.

Another way to think of high pressure inside the eye is to imagine a water balloon. The more water that is put into the balloon, the higher the pressure inside the balloon. The same situation exists with too much fluid inside the eye—the more fluid, the higher the pressure. Also, just like a water balloon can burst if too much water is put into it, the optic nerve in the eye can be damaged by too high of a pressure. See Media files 1-2.

Certain risk factors are associated with the development of glaucomatous damage. The greater the number and the degree of risk factors, the greater the risk of developing glaucoma over time.

The following historical and demographic factors have shown a high association for the disease:

• Family history is a definite risk factor.
  
  
  • Between 10-20% of people with glaucoma have a positive family history.
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  • Family history of glaucoma in a sibling is the greatest risk factor, followed by glaucoma in a parent. One survey found that the risk of having glaucoma is increased 3.7-fold for individuals who have siblings with POAG.
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• Increasing age
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• Race, particularly African American

In addition to elevated IOP, the following eye conditions have been implicated as risk factors for developing glaucoma:

• Glaucoma already present in one eye
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• Congenital abnormalities (abnormalities present from birth): The underlying cause of glaucoma may be from congenital variations in the eye, especially in the appearance of the optic nerve.
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• Onetime trauma to the eye or prior eye surgery: This may indicate that the optic nerve damage is not progressive but may have been because of an isolated incident. The key is whether any progression occurs.
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• Suspicious looking optic nerve or an optic nerve defect
  
  
  • Susceptibility of the optic nerve to damage varies from individual to individual. Along with other risk factors, the likelihood of optic nerve damage also depends on the level of IOP.
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  • Problems with blood supply to the optic nerve may play a role. This is especially important in individuals with normal-tension glaucoma who have progressive disease despite IOP of less than 21 mm Hg. See Normal-Tension Glaucoma.
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• Narrow angles
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• Nearsightedness (myopia)
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• Pseudoexfoliation: Flakes of material are produced inside the eye that obstruct the trabecular meshwork, causing a rise in IOP.
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• Pigment dispersion
  
  
  • The iris releases pigment inside the eye that obstructs the trabecular meshwork, causing a rise in IOP.
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  • With pigment dispersion, the risk of glaucoma increases by 25-50%.
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• History of uveitis or other inflammatory eye disease: Uveitis is an inflammation of the uvea, that is, the iris, the ciliary body, and the choroid.
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• Central retinal vein occlusion: Some people’s first sign of disease from elevated IOP can be sudden vision loss due to the vein in the central part of the retina becoming blocked, called a central retinal vein occlusion.

The following medical conditions have been associated as risk factors for developing glaucoma:

• Current or past use of topical steroids
  
  
  • Topical steroids may elevate IOP in certain people.
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  • Optic nerve damage may occur from a previous episode of increased IOP associated with topical steroid use. The elevation of IOP is usually seen within a few weeks of starting topical steroids.
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• Diabetes
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• History of vasospastic disorders (spasms or constrictions of the blood vessels): Migraine headaches occur more often in people with normal-tension glaucoma.
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• Heart disease, particularly in those with normal-tension glaucoma

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