Tuesday, March 07, 2006

Section 2-B. Epidemiology of Primary Open-Angle Glaucoma

The word “primary” of primary open-angle glaucoma indicates that no specific cause for the disease has been found to date. Primary open-angle glaucoma (POAG) is associated with optic nerve damage with resultant visual loss. However, POAG may or may not be associated with elevated intraocular pressure (IOP). The normal IOP is between 10 and 21 (in millimeters of Mercury or mm Hg). Classically, POAG occurs in a patient with elevated IOP (greater than 21). However, significant portion of POAG patients do not have elevated IOP; this subgroup of patients is often referred to as having “normal tension,” “normal pressure,” or “low tension” glaucoma.

It is estimated that normal pressure glaucoma makes up anywhere from 40-75% of all primary open angle glaucoma. And POAG makes up 85-90% of all glaucomas in the Western world. Prevalence of primary open angle glaucoma has been extensively studied by a number of well-designed clinical studies in different populations. In white populations, primary open angle glaucoma is present in 0.3 to 4.0% of the older population (Table 2-1). In Asian populations, POAG is present in 0.5 to 2.6% of the older population. In the Hispanic population in the United States, POAG is present in 2.0%; however, the number of studies on Hispanic populations is limited. In black populations, the prevalence of POAG is higher and ranges from 2.9 to 8.8% of the older population. It is clear that the black population is at a higher risk of developing POAG than in other populations.

Table 2-1. Prevalence of primary open-angle glaucoma in different world populations.

Race / Location

Prevalence of Primary Open-Angle Glaucoma in older age population
(generally over age 40)

White populations (US, Europe, Iceland, Australia)

0.3 – 4.0 %

Asian populations (Japan, Mongolia, Singapore, India)

0.5 – 2.6 %

Hispanic population (US)

2.0 %

Black populations (US, Caribbean, Africa)

2.9 – 8.8 %


In general, the risk of developing glaucoma is very small in general population (see Table 2-1). However, there are several risk factors that are associated with the development of POAG. As seen in Table 2-1, the black race is one such risk factor. Other risk factors include older age, positive family history of glaucoma, and elevated intraocular pressure. A black person has 4 times the risk of developing glaucoma than a white person. The older you are, the more likely you will develop glaucoma. If your first-degree relative (parent or sibling) has glaucoma, your chance of developing glaucoma increases by 2 to 4 fold. If your intraocular pressure is over 30 (mm Hg), the chance of developing glaucoma is 40 times greater than if the IOP is under 15. Thin cornea, which can lead to IOP measurement error (under-estimation), is also associated with increased risk of glaucoma. In other words if you have thin cornea, your true IOP is higher than what is measured, and you are at a higher risk of developing glaucoma. Additional minor risk factors for glaucoma include myopia (near sightedness), low diastolic blood pressure, and diabetes among others. Normal pressure glaucoma has been associated with migraine headache and Raynaud’s phenomenon (“cold and numb fingers” due to poor peripheral blood circulation).

It is uncommon, but still possible, for patients to become blind from primary open-angle glaucoma. Several studies suggest the risk of becoming blind in one eye for a glaucoma patient can range 15 to 54% over 15-22 year period. The risk of becoming blind in both eyes for a glaucoma patient can range from 4 to 22% over the same period. The risk factors for developing blindness from glaucoma include advanced stage of glaucoma at diagnosis, younger age at diagnosis, poor IOP control, poor compliance with medications, and inadequate treatment and follow-up care. Some of the blindness data are old (from before 1980); with the improvement in treatment over the last 25 years, it is generally believed that the rate of blindness from glaucoma in the 21st century is lower than the figures shown above.

How do we detect glaucoma early so that we can prevent blindness from open-angle glaucoma? There has not been a simple answer. Population screening of intraocular pressure to detect glaucoma has not been very successful, because significant percentage of patients with glaucoma have normal IOP. On the other hand, examining everyone by an ophthalmologist would be prohibitively costly and time-consuming. The American Academy of Ophthalmology recommends a complete eye examination (that includes glaucoma screening) every 2-4 years between ages 40-64, then every 1-2 years after age 65 (Table 2-2). If you have risk factors for glaucoma, additional examinations are recommended.


Table 2-2. Recommended frequency of eye examinations by American Academy of Ophthalmology

Age group

With No glaucoma risk factors

With Glaucoma Risk factors

20-29

At least once during interval

Every 3-5 years

30-39

At least twice during interval

Every 2-4 years

40-64

Every 2-4 years

Every 2-4 years

65

Every 1-2 years

Every 1-2 years



0 Comments:

Post a Comment

Links to this post:

Create a Link

<< Home