The medical community should sit up and take notice whenever a dramatic difference in the prevalence of a disease is identified in a particular population group. Whether it be a laboratory experiment or a cross-sectional survey, as in the article published in this issue of JAMA, "Racial Variations in the Prevalence of Primary Open-angle Glaucoma: The Baltimore Eye Survey,"1 such a study is worthy of widespread attention.
In the United States, where infectious eye diseases are not as prevalent as in third-world countries, glaucoma has become one of the leading causes of blindness.2 Tielsch et al have now shown that primary open-angle glaucoma (POAG) has a remarkably higher prevalence in black members of the US population. Earlier reports pointed to this difference,3-6 but, until now, equivalent data derived from comparisons of subgroups within a single racially mixed population were not available. Given the