Epidemiologic Aspects of Glaucoma

Primary Open-Angle Glaucoma

Magnitude of the problem

Primary open-angle glaucoma (POAG) poses a significant public health problem. The estimated prevalence of POAG in the United States in individuals older than 40 years is 1.86% (95% confidence interval, 1.75%–1.96%), based on a meta-analysis of population-based studies. Applied to data from the 2000 US census, this percentage translates to nearly 2.22 million Americans affected. Estimates based on the available data indicate that between 84,000 and 116,000 of them have become bilaterally blind (best-corrected visual acuity ≤20/200 or visual field <20°). With the rapidly aging US population, the number of POAG patients is estimated to increase by 50%, to 3.36 million in 2020.

The World Health Organization (WHO) undertook an analysis of the literature to estimate the prevalence, incidence, and severity of the different types of glaucoma on a worldwide basis. Using data collected predominantly in the late 1980s and early 1990s, the WHO estimated the global population of persons with high IOP (>21 mm Hg) to be 104.5 million. The incidence of POAG was estimated at 2.4 million persons per year. Blindness prevalence for all types of glaucoma was estimated at more than 8 million persons, with 4 million cases caused by POAG. Glaucoma was theoretically calculated to be responsible for 12.3% of blindness. This makes glaucoma the second leading cause of blindness worldwide, following cataract.

Prevalence

The estimated prevalence (the total number of individuals with a disease at a specific time) varies widely across population-based samples, with the Rotterdam Study (northern European population) showing a prevalence of 0.8% and the Barbados Eye Study (Caribbean population) showing a prevalence of 7% in individuals older than 40 years. But in both of these studies, there is a significant increase in the prevalence of glaucoma in older individuals, with estimates for persons in their 70s being generally 3 to 8 times higher than those for persons in their 40s. In addition, multiple population-based surveys have demonstrated a higher prevalence of glaucoma in specific ethnic groups. Among whites aged 40 years and older, a prevalence of between 1.1% and 2.1% has been reported based on population-based studies performed throughout the world. The prevalence among black persons and Latino persons is up to 4 times higher compared to the prevalence among whites. Black individuals are also at greater risk of blindness from POAG, and this risk increases with age: in persons aged 46–65 years, the likelihood of blindness from POAG is 15 times higher among blacks than that among whites.

Friedman DS, Wolfs RC, O’Colmain BJ, et al. Prevalence of open-angle glaucoma among adults in the United States. Arch Ophthalmol. 2004;122(4):532–538.

Javitt JC, McBean AM, Nicholson GA, Babish JD, Warren JL, Krakauer H. Undertreatment of glaucoma among black Americans. N Engl J Med. 1991;325:1418–1422.

Varma R, Ying Lai M, Francis BA, et al. Prevalence of open-angle glaucoma and ocular hypertension in Latinos: the Los Angeles Latino Eye Study. Ophthalmology. 2004;111(8):1439–1448.

Incidence

The incidence (the number of new cases of a disease that develop during a specific period) of POAG, which has been examined less than the prevalence of POAG in population-based studies, varies widely. The Barbados Eye Study demonstrated, in a predominantly black population, an overall incidence of 2.2% in subjects older than 40 years. A much lower incidence was demonstrated in the Visual Impairment Project, based in Melbourne, Australia (1.1% for definite and probable POAG); and in the Rotterdam Study (5-year risk of 1.8% for definite and probable POAG).

Risk factors

Strictly defined, a factor can be considered a risk factor only if it predates disease occurrence. In prospective studies, a number of risk factors have been found to be associated with progression of glaucoma, including elevated IOP, reduced perfusion pressure, advanced age, thin central corneas, racial background, and a positive family history (Table 1-3). The role of gender and of various systemic factors, such as diabetes, systemic hypertension, and atherosclerotic and ischemic vascular diseases, in the development of glaucoma has been widely debated, and currently available data are inconclusive.

Table 1-3

In terms of the assessment of risk factors, the importance of diurnal variation in IOP has been increasingly recognized. Current evidence, obtained under sleep laboratory conditions, suggests that in most subjects, the peak IOP occurs at night and is therefore not seen in the routine clinical setting.

Dueker DK, Singh K, Lin SC, et al. Corneal thickness measurement in the management of primary open-angle glaucoma: a report by the American Academy of Ophthalmology. Ophthalmology. 2007;114(9):1779–1787.

Hennis AJ, Wu SY, Nemesure B, et al. Nine-year incidence of visual impairment in the Barbados Eye Studies. Ophthalmology. 2009;116(8):1461–1468. Epub 2009 Jun 4.

Leske MC, Heijl A, Hyman L, et al. Predictors of long-term progression in the Early Manifest Glaucoma Trial. Ophthalmology. 2007;114(11):1965–1972.

Primary Angle-Closure Glaucoma

Race

The prevalence of primary angle-closure glaucoma (PACG) varies among different racial and ethnic groups. Among white populations in the United States and Europe, it is estimated at 0.1%. Inuit populations from the Arctic regions have the highest-known prevalence of PACG—20 to 40 times higher than that for whites. Although estimates of the prevalence of PACG in Asian populations vary widely, available data suggest that for most Asian population groups, the prevalence of PACG is between that for whites and that for the Inuit. Some studies have suggested that the prevalence of PACG among blacks is similar to that among whites, with most cases among black persons being of the chronic variety.

Gender

Acute angle-closure glaucoma has been reported more often in women than in men, and several population-based surveys show that women are at increased risk of angle-closure glaucoma. Studies of normal eyes have shown that women have shallower anterior chambers than men.