Elsevier

Survey of Ophthalmology

Volume 48, Issue 3, May–June 2003, Pages 295-313
Survey of Ophthalmology

Major review
Primary Open-Angle Glaucoma in Blacks: A Review

https://doi.org/10.1016/S0039-6257(03)00028-6Get rights and content

Abstract

Glaucoma is one of the leading causes of blindness worldwide. Primary open-angle glaucoma (POAG) is the most prevalent form of glaucoma and has a particularly devastating impact in blacks. In the black American population, POAG prevalence is estimated to be six times as high in certain age groups compared to whites. POAG is more likely to result in irreversible blindness, appears approximately 10 years earlier and progresses more rapidly in blacks than in whites. Racial differences in optic disk parameters have been reported and show that blacks have larger optic disks than whites. This finding is robust and may account for the reported differences in other optic disk parameters. The existence of racial differences in intraocular pressure remains to be demonstrated, as conflicting findings are reported in the literature. Intraocular pressure may actually be underestimated in blacks, perhaps because they have thinner corneas. The prevalence of diabetes and hypertension is higher in blacks than in whites, and although no causal relationship has been established between POAG and each of these systemic diseases, some reports suggest that they often occur together, perhaps through an indirect relationship with intraocular pressure. Compounding the problem, there is evidence that blacks are less responsive to both drug and surgical treatment for POAG. Finally, they often have reduced accessibility to treatment and are less aware of the risks of having POAG. This article provides a comprehensive review of the current knowledge pertaining to POAG in blacks.

Introduction

Glaucoma is one of the leading causes of blindness worldwide.20., 30., 48., 107., 124., 125., 129., 134., 160., 169., 170., 194., 200. Although the number of people affected by the primary glaucomas varies in different reports, it is estimated that approximately 66.8 million people are affected worldwide.134 One of the most prevalent forms is primary open-angle glaucoma (POAG), with approximately 33.1 million sufferers around the world.59., 134. In the United States alone, it is estimated that 2.47 million people are affected by POAG, 130,450 of whom have become bilaterally blind.142 POAG has a serious impact on the quality of life ofa large number of people both in the United States and worldwide.4

Blacks in many areas of the world are disproportionately affected by POAG. Large population-based studies such as the Barbados Eye Study showed that 1 in 11 Afro-Caribbeans over the age of 50 years, and 1 in 6 over the age of 70 years had open-angle glaucoma.100 Another population-based study was conducted in St. Lucia (West Indies), an island composed of a relatively homogeneous black population. Higher prevalence estimates of POAG in blacks 30 years of age and older were reported in St. Lucia, compared to the prevalence estimates reported for whites in other population-based studies.114 Similarly, population-based surveys conducted in African countries have shown the devastating impact of POAG in blacks.8., 22., 38., 148., 151., 187.

In the United States, the Baltimore Eye Survey164., 175. and other studies22., 113., 188., 197. have estimated that prevalence in some age groups may be up to six times as high in black Americans, compared to whites. POAG is the leading cause of irreversible blindness in the black American population164., 183. and early studies suggested that black Americans are more likely to become blind as a result of POAG than are white Americans.63., 68., 195. A more recent study showed that black Americans are 16 times more likely than white Americans to develop POAG-associated visual impairment (i.e., best-corrected visual acuity worse than 20/40 but better than 20/200 in the better-seeing eye).126 Furthermore, POAG progresses more rapidly in blacks.195 A follow-up of the St. Lucia cohort, 10 years after the initial study, showed that visual field progression occurred in 52–73% of untreated glaucoma and glaucoma-suspect eyes.193 POAG appears approximately 10 years earlier in this population.33., 57., 63., 113., 128., 164., 188., 195. Consistent with this trend, David et al39 reported that ocular hypertension appears approximately 12 years earlier in blacks. Furthermore, a higher percentage of blacks than whites (18.1% versus 5.4%) with ocular hypertension go on to develop glaucoma.39., 82.

This article reviews the current knowledge on POAG in blacks. Racial differences in diagnostic factors, risk factors, and treatment methods in blacks will be discussed. Other pertinent issues, such as treatment availability and glaucoma awareness in blacks, will also be reviewed.

That disease prevalence and morbidity may differ according to race is well established. What, then, defines “race” and how is it measured?92 Defining race is much more difficult than it would appear.9 To quote Evelyn Brooks Higginbotham, a noted African American historian and writer, “when we talk about the concept of race, most people believe that they know it when they see it but arrive at nothing short of confusion when pressed to define it.”

Biomedical research has long assumed that phenotype traits like skin color and hair texture can be used to categorize people into meaningful genetic subgroups. Yet, many investigators now assert that there is no genetic basis for racial classification, that biologically distinct races do not exist, and that race as used in the United States is a social and political construct with no basis in science and anthropology.60 The Institute of Medicine in their “Report on Cancer and Ethnic Minorities and the Medical Underserved—1999”, concluded that human biodiversity cannot be adequately summarized according to the broad, presumably discrete categories assumed by a racial taxonomy and recommended using the term “ethnic group.”

The concept of ethnicity is more concerned with cultural distinctions and learned behavior and thus carries less of a biological connotation. However, the use of ethnicity in classifying people in medical research has its own problems with ambiguity.161 For example, there is no single black culture in the United States. A recently emigrated taxi driver from Haiti, a slave-descendent farmer from rural Mississippi, and a young Republican politician from a mixed marriage may all classify themselves as “black,” but will likely have distinct cultural experiences.190

The distinction between race and ethnicity is often blurred in medical research. From the standpoint of health differences, what is measured with the variable “race” is likely to be some combination of culture, genes, and external societal influences.165 The concepts of race and ethnicity are complex, and while acknowledging that self-report is imperfect,5., 185. clinical studies have relied on this method.15., 62. In this article, we use the term “race” rather than “ethnic group” because we believe that the concept of biological race does have some usefulness in clinical medicine, particularly in the assessment of phenotypic differences in attributes that define a particular disease. However, we caution that a strictly biological connotation of race focuses too narrowly on only one of many factors that are likely to be operational in explaining the disparity in the prevalence and morbidity of specific diseases.189

Large population-based studies provide important information on the prevalence of POAG and on risk factors for the disease in blacks. Clinical observations suggesting racial differences in POAG date back to the 1930s.119., 183. However, solid evidence regarding these differences could only be obtained through large population-based studies. These studies offer several advantages over other study designs, including reduced possibility of selection bias, thus providing more accurate prevalence estimates. One of the first population-based surveys was conductedin St. Lucia, in 1989, and it included 1,679 Afro-Caribbeans.114 The Baltimore Eye Survey (5,308 subjects 40 years of age or older, of whom 45% were black Americans) and the Barbados Eye Study (4,631 subjects 40 years of age or older, 93% of whom were Afro-Caribbeans) were later conducted to characterize vision in people of African descent. The two most recent prevalence surveys were conducted in Africa, on Bantu-derived populations. One was conducted in the district of Kongwa, central Tanzania and included 3,268 black East Africans.22 The other was conducted in South Africa, in the Hlabisa district (Northern KwaZulu–Natal Province). This survey examined 1,005 subjects in rural Zululand.

Although the prevalence estimates of POAG reported in these population-based surveys do vary (Table 1), all have reported higher prevalence estimates of POAG in people of African descent compared to whites in other population-based studies. The variability in the prevalence estimates may be due to differences in the definitions, criteria and/or testing methods used to define, diagnose and classify POAG.54 Table 2 provides an overview of such differences that arise between the population-based studies included in Table 1, in making a POAG diagnosis.

Section snippets

OPTIC NERVE

Racial differences in optic nerve parameters between blacks and whites are well documented (Table 3). Larger optic disk areas have been observed in normal,29., 110., 178., 180. post-mortem,136 and glaucomatous113 eyes of blacks. This finding is robust and the differences remain significant after adjusting for the effect of different fundus cameras and topographers.120 Racial differences in other optic disk parameters have also been reported and are listed below; however, they should be

Racial Differences in Risk Factors

Age, elevated IOP, and family history of glaucoma are the most important risk factors for POAG, and diabetes, systemic hypertension, and refractive error are potential risk factors.168 There is evidence suggesting that blacks and whites differ with respect to these factors.10., 81., 87., 102., 150., 172., 198.

Treatment Methods and POAG Management

Glaucoma treatment is aimed at reducing IOP through either drug therapy, surgery, or by a combination of the two methods. There is evidence that blacks may have poorer response to treatment than whites to both methods of treatment.

ACCESSIBILITY TO TREATMENT

Glaucomatous visual loss is often preventable with current drug regimens and surgical techniques, provided that intervention occurs in the early stages of the disease. Although black Americans are a high-risk group, they are less likely than white Americans to initiate POAG treatment.58 Ontiveros et al showed that black Americans are also less likely than white Americans to have a primary care physician and to undergo glaucoma screening, even though all their respondents were eligible for

Conclusion

Noting differences in phenotypic characteristics and responses to treatment between blacks and whites should prove useful in providing optimal ophthalmic care to black populations. It should be noted that blacks have larger disks and thinner RNFL than whites. Although there are conflicting reports, a number of studies have reported elevated IOP levels in untreated blacks compared to whites. Furthermore, blacks have thinner CCTs than whites and thus their recorded IOPs may underestimate their

Method of Literature Search

A search of the MEDLINE database was conducted using the following search words: glaucoma, POAG, African-American, race, racial differences, blacks, prevalence, optic nerve, optic disk, neuroretinal rim area, cup-to-disk ratio, RNFL, intraocular pressure, central corneal thickness, treatment, drugs, medication, surgery, glaucoma awareness, and risk factors. The search covered the years 1967 to July 2002 and articles published in English and in French were included. Additional sources included

References (201)

  • W.M Grant et al.

    Why do some people go blind from glaucoma?

    Ophthalmology

    (1982)
  • L.S Harris et al.

    Effect of ocular pigmentation on hypotensive response to pilocarpine

    Am J Ophthalmol

    (1971)
  • R Hiller et al.

    Blindness from glaucoma

    Am J Ophthalmol

    (1975)
  • K Jamerson et al.

    The impact of ethnicity on response to antihypertensive therapy

    Am J Med

    (1996)
  • H.K Kamel et al.

    Diabetes mellitus among ethnic seniors: contrasts with diabetes in whites

    Clin Geriatr Med

    (1999)
  • I.M Katz et al.

    Effects of iris pigmentation on response of ocular pressure to timolol

    Surv Ophthalmol

    (1979)
  • J Katz et al.

    Estimating progression of visual field loss in glaucoma

    Ophthalmology

    (1997)
  • J Katz et al.

    Risk factors for primary open angle glaucoma

    Am J Prev Med

    (1988)
  • B.E Klein et al.

    Open-angle glaucoma and older-onset diabetes. The Beaver Dam Eye Study

    Ophthalmology

    (1994)
  • B.E.K Klein et al.

    Intraocular pressure in diabetic persons

    Ophthalmology

    (1984)
  • T Krupin et al.

    Argon laser trabeculoplasty in black and white patients with primary open-angle glaucoma

    Ophthalmology

    (1986)
  • S Kumanyika et al.

    Beliefs about high blood pressure prevention in a survey of blacks and Hispanics

    Am J Prev Med

    (1989)
  • B Leblanc et al.

    Binding of drugs to eye melanin is not predictive of ocular toxicity

    Regul Toxicol Pharmacol

    (1998)
  • AGIS

    The Advanced Glaucoma Intervention Study (AGIS): 3. Baseline characteristics of black and white patients

    Ophthalmology

    (1998)
  • AGIS

    The Advanced Glaucoma Intervention Study (AGIS): 4. Comparison of treatment outcomes within race. Seven-year results

    Ophthalmology

    (1998)
  • AGIS

    The Advanced Glaucoma Intervention Study (AGIS): 9. Comparison of glaucoma outcomes in black and white patients within treatment groups

    Am J Ophthalmol

    (2001)
  • W.L Alward

    The genetics of open-angle glaucoma: the story of GLC1A and myocilin

    Eye

    (2000)
  • H Amaro et al.

    Criollo, mestizo, mulato, LatiNegro, indigena, white, or black? The US Hispanic/Latino population and multiple responses in the 2000 census

    Am J Public Health

    (2000)
  • M.F Armaly et al.

    Biostatistical analysis of the collaborative glaucoma studyI. Summary report of the risk factors for glaucomatous visual-field defects

    Arch Ophthalmol

    (1980)
  • J.A Bachman

    Juvenile onset primary open-angle glaucoma: three case studies and review

    J Am Optom Assoc

    (1998)
  • R.S Bartholomew

    Glaucoma in a South African black population

    S Afr Arch Ophthalmol

    (1976)
  • M.T Bassett

    The pursuit of equity in health: reflections on race and public health data in Southern Africa

    Am J Public Health

    (2000)
  • B Bengtsson

    Some factors affecting the distribution of intraocular pressure in a population

    Acta Ophthalmol (Copenh)

    (1972)
  • B Bengtsson

    Aspects of the epidemiology of chronic glaucoma

    Acta Ophthalmol Suppl

    (1981)
  • W.E Benson et al.

    Diabetes and Its Ocular Complications

    (1988)
  • U Boehmer et al.

    Self-reported vs administrative race/ethnicity data and study results

    Am J Public Health

    (2002)
  • N.S Borisuth et al.

    The risk profile of glaucoma filtration surgery

    Curr Opin Ophthalmol

    (1999)
  • C.F Bosworth et al.

    Motion automated perimetry identifies early glaucomatous field defects

    Arch Ophthalmol

    (1998)
  • P.J Bucher et al.

    Prevalence and causes of blindness in the northern Transvaal

    Br J Ophthalmol

    (1988)
  • W.M Budde et al.

    Influence of optic disc size on neuroretinal rim shape in healthy eyes

    J Glaucoma

    (2000)
  • R.R Buhrmann et al.

    Prevalence of glaucoma in a rural East African population

    Invest Ophthalmol Vis Sci

    (2000)
  • L Cantor et al.
    (1997)
  • J Caprioli et al.

    Optic disc rim area is related to disc size in normal subjects

    Arch Ophthalmol

    (1987)
  • J Caprioli et al.

    Videographic measurements of optic nerve topography in glaucoma

    Invest Ophthalmol Vis Sci

    (1988)
  • L Carter-Edwards et al.

    Knowledge of diet and blood pressure among African Americans: use of focus groups for questionnaire development

    Ethn Dis

    (1998)
  • B.C Chauhan

    The value of high-pass resolution perimetry in glaucoma

    Curr Opin Ophthalmol

    (2000)
  • T Chi et al.

    Racial differences in optic nerve head parameters

    Arch Ophthalmol

    (1989)
  • M.C Chirambo et al.

    Ophthalmology in Malawi

    Arch Ophthalmol

    (1989)
  • I.A Chisholm et al.

    Prognostic indicators in ocular hypertension

    Can J Ophthalmol

    (1980)
  • R.S Cooper et al.

    Prevalence of NIDDM among populations of the African diaspora

    Diabetes Care

    (1997)
  • Cited by (186)

    • Cataract surgery and Hydrus stent implantation in juvenile open-angle glaucoma: A case report

      2022, Journal of the National Medical Association
      Citation Excerpt :

      Glaucoma is a chronic optic neuropathy characterized by increased intraocular pressure (IOP), optic disc cupping, and vision loss. It is a leading cause of blindness worldwide.1 Juvenile-onset open-angle glaucoma is a rare subset of primary open-angle glaucoma (POAG).2

    • Epidemiology of glaucoma in Burkina Faso: Determination of the prevalence and circulating glaucomatous phenotypes in Ouagadougou

      2022, Journal Francais d'Ophtalmologie
      Citation Excerpt :

      Being a multifactorial disease, the occurrence of glaucoma would be under the influence of a genetic and environmental components. Predisposition genes would play a very important role, however there are other major risk factors such as advanced age, ethnicity, family history, high intraocular pressure (IOP), diabetes and high myopia, which can significantly increase the risk of developing glaucoma [7,8,10,11]. The only parameter that can be acted upon in the management of glaucoma is IOP.

    View all citing articles on Scopus

    The authors wish to thank Dr. Tarek El Beltagi for reviewing earlier versions of the manuscript and Ms. Shannon Kleinhandler for her assistance. This article was supported by NIH grants EY08208 (PAS) and EY11008 (LZ), and the Glaucoma Research Foundation (PAS). The authors reported no proprietary or commercial interest in any product mentioned or concept discussed in this article.

    View full text