Last Updated: January 2005

add to my folder | print page

Epidemiology of Glaucoma

Studies have shown that glaucoma is the second leading cause of blindness in the United States [Leske, 1983] as well as the second leading cause of bilateral blindness in the world [Quigley, 1996]. An obvious question becomes, "What is the first leading cause of blindness"? The answer is not simple since it is both age and race dependent.

In a random sample from Salisbury, Maryland, 2,520 Medicare patients agreed to participate in a prospective study and have their eyes tested [Munoz et al., 2000]. The presence of bilateral visual acuity less than 20/40 increased from 4% in those 65 - 74 years old to 16% in those 80 - 84 years old. Of all participants, 21 (0.83%) were bilaterally blind. Of these 21 patients:

43% were blind from age related macular degeneration,
10% were blind from diabetic retinopathy,
10% were blind from glaucoma, and,
37% were blind from other causes.

In a cluster-stratified random sample from both rural and urban regions of Australia, the predominantly Caucasian participants had a mean age of 59; each received a standardized eye examination [Weih et al., 2000]. Visual impairment was classified using both visual field loss and visual acuity loss. Their data show that of their 5,147 participants, age-related macular degeneration was responsible for the most cases of visual impairment (n = 87). By comparison, glaucoma was responsible for 26 cases and diabetic retinopathy for 7 cases.

In the United States, glaucoma is a common reason for patients to visit their ophthalmologist. Among patients over 65 years of age, between the years 1991 and 1992 glaucoma was the third most frequently reported reasons for a visit to the physician for a disease amongst all diseases [Schappert, 1995]. It was estimated that in 2000, United States residents would make 8.8 million office visits for glaucoma [Quigley et al., 1997]. In 2000, the number of people in the United States with primary open angle glaucoma (POAG) was estimated to be 2.47 million, i.e. 1.84 million white and 619,000 African Americans [Quigley et al., 1997].

Prevalence of open angle glaucoma

Prevalence refers to the number of patients with a disease as a percentage of a specified population. Good data on the prevalence of glaucoma are currently available although incidence data on POAG are not [Tielsch, 1996]. The Beaver Dam Eye study was conducted in Beaver Dam, Wisconsin (n = 4,926) [Klein et al., 1992] where the sample was predominantly Caucasian. OAG was defined by identifying any of the following three clinical parameters: high IOP, abnormal visual field, or a cup to disc ratio that was either large or asymmetric. The overall prevalence of OAG was 2.1%. Prevalence increased with age:

0.9% in participants 43 to 54 years old, and,
4.7% in participants 75 years of age or older.

Gender was not influential. Of the 104 participants with definite OAG, about one third had IOPs less than 22 mm Hg, i.e. low tension glaucoma, also known as normal tension glaucoma. The authors conclude that the prevalence of OAG in Beaver Dam was comparable to other Caucasian populations.

By comparison to the Beaver Dam Eye study with a predominantly Caucasian population, the Baltimore Eye Survey was a cross-sectional study with a multiracial population. In the Baltimore Eye Survey [Tielsch et al., 1991] 5,308 participants received an ophthalmological screening examination. Of this sample, 2,395 were African American and 2,913 were Caucasian Americans. POAG was defined on the basis of glaucomatous optic nerve damage, abnormal visual fields or both. Intraocular pressure was not a criterion.

For African Americans, prevalence rates were dependent upon age:

1.2% for those in the 40 to 49 year, and,
11.3% for those older than 80 years.

For Caucasian Americans, the prevalence rates were also dependent upon age:

0.9% in the 40 to 49 year, and,
2.2% in those older than 80 years.

The age-adjusted prevalence rate for African Americans compared with white Americans was 4 to 5 times higher underscoring a substantially higher risk for African Americans with respect to POAG. Gender did not influence prevalence in either African Americans or white Americans.

Although African Americans comprise 14.7% of the United States population, they comprise 25.1% of all patients with OAG [Quigley et al., 1997]. Using a cohort size of 100,000, 3.9% of the person-years in the African American cohort would be affected by glaucoma, about four times as many as a cohort of 100,000 Caucasian participants. African Americans were shown to develop glaucoma about 6 to 10 years earlier than Caucasian Americans and had open angle glaucoma (OAG) longer than the average Caucasian American:

African Americans = about 16 years,
Caucasian Americans = about 13 years.

In a population-based study of Hispanic subjects, detailed ocular examinations were conducted in eligible adults who lived in Nogales and Tucson, Arizona [Quigley et al., 2001]. OAG was defined using threshold visual field defect and optic disc damage parameters (and not IOP). About 4,800 subjects were examined. The overall prevalence was 1.97% (95% confidence interval, 1.58%-2.36%). Prevalence rates were dependent on age.

0.5% in the 40 to 49 year, and,
12.6% in those older than 80 years.

Only 36 (38%) of the 94 subjects with OAG knew they had OAG prior to the study. If patients were screened using an IOP higher than 22 mm Hg as the only criterion, 80% of the OAG cases would have been missed.

The prevalence of OAG is Hispanic subject is intermediate between Caucasian Americans and African Americans. In the Hispanic population sampled, glaucoma was the leading cause of bilateral blindness.

Prevalence of OAG as a function of age in Hispanic persons is shown in the figure below. A comparison is also made with the prevalence of OAG in Black persons as a function of age based upon a previous study.

A similar comparison of prevalence of OAG as a function of age is shown below for Hispanic persons and White persons.

Prevalence of narrow angle glaucoma

Estimates of prevalence for narrow angle glaucoma are difficult to find in the literature. In the Baltimore Eye Study, the prevalence of narrow angle glaucoma was:

0.4% in Caucasian Americans, and,
0.9% in African Americans.

From a review of nine studies, the median age-adjusted prevalence was 0.1% (range, 0.04% to 0.69%) for Caucasians older than 40 years [Quigley et al., 1997]. These authors note that there was a trend for the frequency of angle-closure glaucoma to increase with age. In the Beaver Dam Eye Study [Klein et al., 1992], only 2 participants out of 4,926 had definite narrow angle glaucoma and its occurrence was deemed by the authors to be rare.

Among Hispanic subjects living in Arizona, the prevalence of angle closure glaucoma was 0.1% (95% CI, 0.03% - 0.24%) [Quigley et al., 2001]. The average age of those with angle closure glaucoma was 76 years.

Compared with Caucasian Americans, the prevalence of angle closure glaucoma among Eskimos is 20 to 40 times higher. Population based studies of the Chinese suggest that their rates are 10 to 15 times higher than Caucasians. In a study conducted jointly in Baltimore, Maryland and Jin Shan, Taiwan, the anterior chamber depth of 531 Chinese, 188 African Americans and 170 Caucasian Americans were evaluated [Congdon et al., 1997]. Within the Chinese cohort, 14 cases of primary angle closure glaucoma were identified compared with none in either the African American or the Caucasian American cohorts. Although the radius of corneal curvature was less for the Chinese than among the African Americans or Caucasian Americans, neither the average anterior chamber depth nor their axial length was significantly different between these three cohorts. This cohort of Chinese with primary anterior chamber angle glaucoma had the following characteristics. They were:

significantly older,
had shorter axial lengths, and,
had shallower anterior chamber depths than the normal participants.

In a related study conducted in Mongolia, 1,610 participants aged 40 years or older were evaluated [Devereux et al., 2000]. In this sample of east Asians, the prevalence for primary angle closure glaucoma was 0.8%.

Incidence of open angle glaucoma

Incidence refers to the number of new cases identified during a specific time interval for a defined population. Incidence data is useful in estimating the risk of OAG development and studying some of the underlying risk factors.

As described above, race significantly impacts epidemiological data with regard to OAG and the racial blend of the sample must be considered. Olmsted County, Minnesota is predominantly Caucasian with considerable Scandinavian ancestry. In a retrospective incidence study, the Rochester Epidemiology Project database was used to access information on the 60,666 residents of Olmsted county. During the study interval, 114 patients were identified with newly diagnosed OAG [Schoff et al., 2001]. Out of these 114 patients with OAG, 102 (89%) had POAG, primary open angle glaucoma. From these data, the overall gender and age-adjusted annual incidence rate was about 14.5 per 100,000. Gender did not have a significant effect on incidence. The overall age-adjusted mean annual incidence rate for women was 15.3 vs. 12.7 for men. The incidence increased with age:

2 per 100,000 in the fourth decade to
94 per 100,000 in the eighth decade.

Incidence of angle closure glaucoma

The Baltimore Eye Survey was a cross-sectional study conducted in a multiracial urban area. In this study [Patel et al., 1995], 4,870 participants were dilated as part of the screening examination. Although none developed acute angle closure glaucoma, 38 patients who were referred did have occludable angles based on gonioscopy. A history of glaucoma was useful in predicting an occludable angle in African Americans. By comparison, a shallow anterior chamber identified on penlight examination was useful in predicting an occludable angle in Caucasian Americans. In the following figure, penlight examination of anterior chamber depth is shown.

Note that in the illustration of the shallow anterior chamber angle shown above, the bowing forward of the iris results in a shadow being cast on to the iris when a penlight is shown in from the side.

Furthermore, participants over the age of 70 were 3 times more likely to have an occludable angle compared with those 40 to 69 years of age.

From a review of nine studies, there was a lower incidence of angle-closure glaucoma among African Americans compared with Caucasian Americans [Quigley et al., 1997]. Predicted prevalence estimates were used to calculate incidence rates of OAG for African American and Caucasian adults by age, per 100,000 persons/year. Incidence rose with age and its increase with age was greater than for Caucasian adults.

In Italy, the age-adjusted incidence of angle closure glaucoma was 3.5 cases per 100,000 [Dal Ri et al., 1990].

Risk of blindness from glaucoma

In the Baltimore Eye Survey, causes of blindness were factored by race [Sommer et al., 1991]. Of these participants, 64 were bilaterally blind. Of these 64, POAG was the cause in:

19% of cases among African Americans compared with,
6% of cases among Caucasian Americans.

Age related macular degeneration was the leading cause of blindness among Caucasian Americans.

In the retrospective, longitudinal study of Olmsted County residents in Minnesota, there were 295 patients who were newly diagnosed and treated for OAG [Hattenhauer, et al., 1998]. The mean follow-up interval was 15 years. Legal blindness was defined as:

corrected visual acuity less than or equal to 20/200,
visual field constriction to 20 degrees or less, or,
both.

Using Kaplan-Meier cumulative probability, after 20 years of follow-up glaucoma related blindness was:

27% in at least one eye, and, 9% in both eyes.

The authors comment that in this Caucasian population, the risk of blindness from treated OAG was considerable.

Using a 5% random sample of Medicare claims from 1986 through 1988, the population-based rates of laser and incisional surgery for OAG among African and Caucasian Americans were determined [Javitt et al., 1991]. There were 1,821 African Americans and 9,481 Caucasian Americans with glaucoma who were evaluated. The rate of surgical treatment for glaucoma among African American Medicare beneficiaries was 2.2 times greater than the rate for Caucasian American Medicare beneficiaries. Based on the conservative estimate that the prevalence rate is 4 times greater among African Americans than Caucasian Americans, the overall observed rate of glaucoma surgery was 45% less than expected. The authors suggest that this lower than expected rate of surgery among African Americans partially accounts for their higher rate of blindness. The rates reported of blindness due to glaucoma were between 6 and 8 times higher among African Americans compared with Caucasian Americans.

In a later study, a retrospective cohort analysis was performed on all trabeculectomy and argon laser trabeculoplasty surgical claims to the Health Care Financing Administration between 1991 and 1994, a 4 year interval [Devgan et al., 2000]. In this study, there were 30,495 African American patients and 160,792 Caucasian American patients. Similar to the 1991 study above, the age-sex adjusted rate ratio for the surgical treatment of glaucoma in African Americans compared to Caucasian Americans was 2.14. These authors concluded that African Americans undergo glaucoma surgery at a rate about 47% less than expected. They further comment that rate of surgical undertreatment remains similar to the earlier study despite efforts by national, state, and local organizations to raise the level of awareness about glaucoma.

High IOP and survival

Using data from the Framingham Eye Study, participants over the age of 70 were evaluated [Hiller et al., 1999]. Three strata were discerned based on IOP:

less than or equal to 20 mm Hg, n = 1,421;
20 to 24 mm Hg (intermediate IOP), n = 264;
greater than or equal to 25 mm Hg (high IOP); n = 79.

Using an age and sex adjusted Cox proportional hazards model, the death rate ratio was 1.04 for those with intermediate IOPs and 1.56 for those an IOP greater than or equal to 25 mm Hg. The authors conclude that a high IOP is a marker for decreased life expectancy in this cohort.

Economic issues related to the treatment of glaucoma

A two-year observational retrospective chart review was conducted to review the costs associated with newly diagnosed POAG (71%) and ocular hypertension (27%), [Kobelt-Nguyen, et al., 1998]. The authors acknowledge that because the patients in this study are newly diagnosed, they are not representative of the entire glaucoma population.

In the American component of this study, one teaching hospital, 2 eye clinics and four large private practices were included. The charts of 264 patients with either POAG or ocular hypertension were reviewed from 1992 through 1994. In this cohort of patients, about half had either moderate or severe optic nerve head damage in the study eye.

During these two years, the average patient made 9.4 visits to specialists and 1.6 visits to a nurse; on average, 4 tests were run per patient. Between 60% and 80% of the resources were used during the first year. Consequently about 70% of the associated costs occurred during the first year. For patients with POAG, the mean total two-year cost was $2,188 per patient. The variation in resource utilization and costs between centers was substantial. The severity of the optic nerve damage did significantly impact treatment costs.

The authors observed that the more the IOP could be decreased in the beginning of treatment, the lower the treatment costs would be over the next two years. At the end of two years, the average IOP was 18 mm Hg.

References

Congdon NG, Youlin Q, Quigley H, et al. Biometry and primary angle-closure glaucoma among Chinese, White, and black populations. Ophthalmology 1997;104:1489-1495.

Dal Ri E, Luraschi M, Davi L, et al. Epidemiologia del glaucoma acuto primaril da chiusura d'angolo: studio di incidenza. Boll Ocul 1990;69(suppl 3):31-39.

Devereux JG, Foster PJ, Baasanhu J, et al. Anterior chamber depth measurement as a screening tool for primary angle-closure glaucoma in an East Asian population. Arch Ophthalmol. 2000;118:257-263.

Devgan U, Yu F, Kim E, et al. Surgical undertreatment of glaucoma in black beneficiaries of Medicare. Arch Ophthalmol 2000;118:253-256.

Hattenhauer MG, Johnson DH, Ing HH, et al. The probability of blindness from open-angle glaucoma. Ophthalmology 1998;105:2099-2104.

Hiller R, Podgor MJ, Sperduto RD, et al. High intraocular pressure and survival: the Framingham Studies. Am J Ophthalmol 1999;128:440-445.

Javitt JC, McBean AM, Nicholson GA, et al. Undertreatment of glaucoma among black Americans. N Engl J Med 1991;325:1418-1422.

Klein BE, Klein R, Sponsel W, et al. Prevalence of glaucoma. The Beaver Dam Eye Study. Ophthalmology. 1992;99:1499-1504.

Kobelt-Nguyen G, Gerdtham U, Alm A. Costs of treating primary open-angle glaucoma and ocular hypertension: a retrospective, observational two-year chart review of newly diagnosed patients in Sweden and the United States. J Glaucoma. 1998;7:95-104.

Leske MC. The epidemiology of open-angle galucoma: a review. Am J Epidemiology 1983;118:166-191.

Munoz, B, West SK, Rubin G, et al. Causes of blindness and visual impairment in a population of older Americans. Arch Ophthalmol. 2000;118:819-825.

Patel KH, Javitt JC, Tielsch JM, et al. Incidence of acute angle-closure glaucoma after pharmacologic mydriasis. Am J Ophthal 1995;120:709-717.

Quigley HA. The number of persons with glaucoma worldwide. Br J Ophthalmol 1996;80:389-393.

Quigley HA and Vitale S. Models of open-angle glaucoma prevalence and incidence in the United States. Invest. Opthalmol. Vis. Sci. 1997;38:83-91.

Quigley HA, West S, Rodriguez J, et al. The prevalence of glaucoma in a population-based study in Hispanic subjects. Proyecto VER. Arch. Ophthalmol. 2001;119:1819-1826.

Schappert SM. Office visits fro glaucoma: United States, 1991-1992. Public Health Service. Centers for Disease Control and Prevention. Advance Data. Hyattsville, MD: National Center for Health Statistics. 1995;262:1-13.

Schoff EO, Hattenhauer MG, Ing HH, et al., Estimated incidence of open-angle glaucoma in Olmsted County, Minnesota. Ophthalmology 2001;108:882-886.

Sommer A, Tielsch JM, Katz J, et al. Racial differences in the cause-specific prevalence of blindness in East Baltimore. N Engl J Med 1991;325:1412-1417.

Tielsch, JM, Sommer A, Katz J, et al. Racial variations in the prevalence of primary open-angle glaucoma. JAMA 1991;266:369-374.

Tielsch JM. The epidemiology and control of open angle glaucoma: a population-based perspective. Annu. Rev. Public Health. 1996;17:121-136 p. 127.

Weih LM, Van Newkirk MR, McCarty CA, et al. Age-specific causes of bilateral visual impairment. Arch Ophthalmol. 2000;118:264-269.

20550256(1)-02/05-EBS-PHY