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Glaucoma Part III

Glaucoma Part III: Understanding Glaucoma and
Its Risk Factors 		 
Date: January 21, 2007

Glaucoma is the second leading cause of irreversible blindness in the United States. Historically, glaucoma has been viewed as a disease caused by increased eye pressure. The current view is that glaucoma represents a common end stage clinical presentation of several different diseases. To understand this view, think of heart failure - which is not a disease but a clinical end stage because of many diseases like high blood pressure, and coronary artery disease. Glaucoma is similarly regarded as a final common end stage pathway of a number of different conditions. While high eye pressure is the most important risk factor for the development and progression of glaucoma, it is still only a risk factor and not the disease itself.

Over the years, numerous investigators have studied the characteristics of individuals who have glaucoma, and based on those studies it became possible for them to identify several factors that seem to occur more frequently in glaucoma patients. Since there is a greater likelihood of these factors being present in someone with glaucoma, it is reasonable to assume that these are considered as risk factors for glaucoma. Any individual who has these risk factors should be screened for the possibility of glaucoma. It is estimated that approximately 10 patients per 1000 patients with glaucoma risk factors will develop glaucoma per year.

Patients with glaucoma risk factors are followed as "Glaucoma suspects". How strong is the suspicion? That depends upon the number of risk factors present. If the screening tests identify you as having risk factors for glaucoma, then a more rigorous follow-up schedule is needed. Serial examinations and continuity of care are critical for glaucoma diagnosis and management. One-time examinations do not have the same value.

Strong Risk Factors
  • High Intraocular (Eye) Pressure: The generally accepted normal mean eye pressure (intraocular pressure - IOP) value is 15.5 mmHg. The normal pressure can range from 10 to 21 mmHg. It is well recognized that some eyes undergo extensive glaucoma damage even when the pressure is in the "normal" range, while others suffer no damage with pressure well above 21 mmHg. Despite this, the value of 21 mmHg has been historically accepted as a good way to separate the "normal" eye pressure from a pressure level which should be viewed with suspicion for glaucoma. You must understand however, that just because you have eye pressure above 21 mmHg does not mean that you have glaucoma. What it does mean is that you are at a higher risk of developing glaucoma.
  • Aging: Everyone over age 60 has an increased risk for glaucoma. Other groups at increased risk include African Americans over age 40.
  • Positive family history of glaucoma in a first degree relative: Glaucoma tends to run in families. In the Baltimore Eye Study, the risk of having glaucoma was approximately 3.7-fold higher for individuals who had a sibling with glaucoma. In the Rotterdam Eye Study, the risk of having glaucoma was 9.2-fold for individuals who had a relative with glaucoma. It seems that glaucoma development depends not so much on a single gene but rather upon the interaction of several genes and possibly environmental factors too.
  • Race: In a study funded by the National Eye Institute, researchers at The Johns Hopkins University reported that glaucoma is three to four times more likely to occur in African Americans than in Caucasians. In addition, glaucoma is six times more likely to cause blindness in African Americans than in Caucasians
  • Suspicious optic nerve appearance. The optic nerve will take on a characteristic appearance once damage from glaucoma has occurred.
  • Central corneal thickness less than 555 microns (0.5 mm): The National Eye Institute supported Ocular Hypertension treatment study (OHTS) has identified corneal thickness as a strong risk factor for developing glaucoma. Patients with a corneal thickness less than 555 microns have a three fold greater risk of developing glaucoma as compared with those who's cornea are more than 588 microns thick.
Other Significant Risk Factors

High Myopia or near-sightedness. Nearsighted patients have a twofold to threefold increased risk of glaucoma compared with those who are not nearsighted. In addition, most studies support a strong association between Diabetes and Glaucoma. Hypertension and other vascular diseases also increase the risk of developing glaucoma. Eye Injuries, previous eye surgery, history of steroid use, sleep-related breathing disorders and male gender all show a clinically significant increase in the number of glaucoma patients.

As you can see history alone can provide your eye doctor with a large part of your diagnosis. Equally impressive is the technology now available to help make a definitive clinical diagnosis. Objective testing with instruments like the GDx, OCT, visual field, Visante, and pachymeter have dramatically increased our ability to diagnose glaucoma years earlier than previously. Visit our column next week where we will emphasize new technology in the diagnosis of glaucoma.