Interestingly, there was a higher rate of conversion in this cohort than described in the previous outcome report published in 2002.2 Among untreated African Americans, the conversion rate to glaucoma was 16.1% versus 8.4% in those individuals who received treatment.1 When contrasting these numbers with the conversion rates for the overall group (9.5% untreated vs 4.4% treated), one might at first conclude that race matters. Closer inspection of the risk factors and multivariate analyses of the data, however, reveals that race failed to reach a level of statistical significance. Many of the African Americans in this cohort had significant risk factors such as thin corneal measurements and high cup-to-disc ratios, and these factors apparently accounted for the higher rates of conversion noted. I would argue that race does not matter in glaucoma.
A TERM IN QUESTION
Is it surprising that race was not a statistically significant factor in the recent report from the Ocular Hypertension Treatment Study? Not really, particularly when one considers that the term race is born of social and political constructs. For at least the last 10 years, many geneticists, evolutionary biologists, and anthropologists have abandoned the notion that there is a biological basis for racial classification.3 Because the human genome project has determined that the human race derives from a single genetic source and that human beings share 99.9% of their genes, it is apparent that classifying the human population into three, four, and perhaps even eight groups was purely arbitrary.4
The significant genetic admixture that has occurred over the last 200,000 years at minimum means that there is no true separation among populations (at least as regards classification that can be reduced to the single digits). Nineteenth-century naturalists such as Samuel Morton and Louis Agassiz used faulty methods of investigation to support preconceived hypotheses.5 Questions regarding this issue of race are slowly permeating the public consciousness, as evidenced by the findings of the 2000 US Census, in which 800,000 individuals identified themselves as both African American and Caucasian.6 How credible is a classification that is based on invalid and mutable information?
WHAT DOES MATTER?
If race is not important, then what is? Glaucoma is known to be heritable. In fact, having a first-degree relative with glaucoma has been estimated to increase an individual's risk of developing glaucoma at least sevenfold. Family history is based on the patient's own report, however, which is often not verified and is subject to the variable definition of glaucoma by the professional community. Nevertheless, family history is a better starting point for determining the influence of heritage than a broader term such as race.
In the absence of a known family history, ethnicity or at least place of origin may be considered as surrogates. Thus, the prevalence of open-angle glaucoma among Mexican Americans (recently reported to be 4.74%)7 is a helpful statistic for this particular ethnic group. Would it be relevant to the Mexicans who trace their origin to a different part of Mexico or South America, however? If the patient sitting in the exam lane was born in Barbados, knowing that the prevalence of open-angle glaucoma among islanders in Barbados is 6.6%8 is helpful, particularly if the patient does not know his or her family history. Although ethnicity may be considered as imprecise a term as race, it is a better starting point when characterizing specific populations. Nonetheless, family history is a superior measure of an individual's genetic heritage.
THE SPECIFICS
The Ocular Hypertension Treatment Study has provided clinicians with the means to break through the myth of race. Molecular geneticists have embarked on an international project entitled the “HapMap Project,” which seeks to consolidate approximately 10 million single nucleotide polymorphisms into a more manageable 500,000 blocks and possibly correlate these blocks with specific populations.9 Until a more refined method of determining genetic lineage becomes available, I believe it is important to measure specific biological findings in any given patient. A thin central cornea combined with a large cup-to disc ratio appears to impart a higher risk of conversion to glaucoma, regardless of treatment.
Until practitioners can assess a patient's individual genetic profile, they must continue to ask about family history and, to the best of their ability, clarify that history with additional questions. Did your mother go blind before she died? Did she ever undergo a procedure on her eyes other than cataract surgery? Was she treated with eye drops? Race does not matter because it is a term that has no biological basis.
Eve J. Higginbotham, MD, is Professor and Chair, Department of Ophthalmology and Visual Sciences, University of Maryland School of Medicine, Baltimore. Dr. Higginbotham may be reached at (410) 328-5929; fcwejh6786@aol.com.
1. Higginbotham EJ, Gordon MO, Beiser JA et al. The Ocular Hypertension Treatment Study. Topical medication delays or prevents primary open-angle glaucoma in African American individuals. Arch Ophthalmol. 2004:122:813-820.
2. Kass MA, Heuer D, Higginbotham EJ, et al. The Ocular Hypertension Treatment Study: a randomized trial determines that topical ocular hypotensive medication delays or prevents the onset of primary open-angle glaucoma. Arch Ophthalmol. 2002:120:701-703.
3. Cavalli-Sforza LL, Nenozzi P, Piazza A. The History and Geography of Human Genes. Princeton, NJ: Princeton UP; 1994.
4. Graves J. The Emperor's New Clothes. Biological Theories of Race at the Millennium. New Brunswick, NJ: Rutgers UP; 2002.
5. Wolpoff M, Caspari R. Race and Human Evolution: A Fatal Attraction. Philadelphia, PA: Basic Books; 1998.
6. Schwartz RS. Racial profiling in medical research. N Engl J Med. 2001:344:1392-1393.
7. Varma R, Ying-Lai, M, Francis B, et al. Prevalence of open-angle glaucoma and ocular hypertension in Latinos. Ophthalmology. 2004;111:1439-1448.
8. Leske MC, Connell AM, Schachat AP, et al. The Barbados Eye Study: prevalence of open-angle glaucoma. Arch Ophthalmol. 1994;112:821-829.
9 . National Institutes of Health. National Human Genome Research Institute Web site. International HapMap Project. Available at: http://www.genome.gov/10001688. Accessed October 5, 2004.
