Certain Asian populations are at a greater risk for the disease
Most glaucoma specialists know that the Asian population is usually at higher risk for glaucoma. A study published in Ophthalmology further pinpoints which Asian ethnic groups are at the greatest risk for which types of glaucoma.
The study was led by Joshua D. Stein, M.D., Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor.
The study also shows a greater risk than previously thought for open-angle glaucoma (OAG) among the Asian-American population.
"While it was once thought that open-angle glaucoma was relatively uncommon among individuals of Asian descent, in this study we were somewhat surprised to find that the risk of open-angle glaucoma among Asian Americans as a group was
actually 50% higher than that of non-Hispanic whites," Dr. Stein said.
Crunching the numbers
Dr. Stein and co-investigators examined data from approximately 2.25 million eyecare patients over the age of 40 who were enrolled in a managed-care network between 2001 and 2007. Patients had to have been in the analyzed database for more than a year and had to have one or more appointments with their eyecare provider. Investigators tracked the prevalence rates of OAG,
narrow-angle glaucoma (NAG), and normal-tension glaucoma (NTG) according to race and Asian ethnicity. Statistical analyses comparing
glaucoma rates against patients of different races were also performed.
Investigators identified the race and ethnicity of each person in the study with the use of public records (specifically, drivers licenses) and a tool called E-Tech (Ethnic Technologies, South Hackensack, N.J.) that assigns a race and ethnicity to the census block of that person's home address. Asian ethnicities included in the study were Chinese American,
Filipino American, Indian American, Japanese American, Korean American, Pakistani American, and
Vietnamese American. There were not enough data to gather information on several other ethnicities, such as Bangladeshi, Thai, Indonesian, and Sri Lankan, so they were grouped in an "Other" category.
And the results?
The study found the OAG prevalence rate for Asian Americans was 6.52%, which was similar to that of Latinos (6.40%). That compared with a prevalence of 5.59% in non-Hispanic whites. Asian Americans also had a higher prevalence for NAG and NTG.
"After adjustment for potential confounding factors, Asian Americans had a 51% increased hazard of OAG, a 123% increased hazard of NAG, and a 159% increased hazard of NTG compared with non-
Hispanic whites," the investigators wrote.
Eight-five percent (1.92 million) of patients in the study had a documented ethnicity. Among those, the investigators were able to further track incidence and prevalence. The prevalence of OAG was highest in Japanese Americans (9.49%), second to Indian and Pakistani Americans (7.78% and 7.70%, respectively). Japanese Americans had a 3- to 10-times higher incidence of NTG than other Asian ethnicities. The prevalence of NAG was highest among Chinese Americans (4.08%) and Vietnamese Americans (3.74%),
percentages that were considerably higher compared with other Asian ethnicities. All Asian ethnicities
had a higher prevalence of NAG compared with non-Asians.
The actual reasons for the higher rates in some ethnicities are not clear, Dr. Stein said. "It may be due to genetic factors, environmental factors, or other factors."
Taking a closer look in the clinic
This study sheds light on specific ethnic risk among the Asian population—the second fastest-growing minority in the U.S.—versus classifying all Asian Americans in the same group, said Douglas J. Rhee, M.D., associate professor, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston.
These study results should push clinicians to more carefully consider patient backgrounds when determining glaucoma risk, Dr. Stein said.
"When ophthalmologists and optometrists evaluate Asian Americans, they should have a low threshold to perform gonioscopy to check the angle anatomy for narrow
angles, especially in individuals of Chinese and Vietnamese ancestry," he said. Clinicians can also have a higher index of suspicion for NTG in Japanese Americans based on these results, he said. "Given the influx of Asian Americans over the past decade and projections that this group will continue to grow in number over the coming years, as these individuals age, health policy makers will need to allocate additional resources in
diagnosing and treating glaucoma in this patient population," Dr. Stein said. "With increasing numbers of these individuals in the United States, it is important that ophthalmologists apply different risk assessments than we generally use for
primary open-angle glaucoma, which is more prevalent in the U.S. Caucasian population," said Louis B. Cantor, M.D., chairman and professor of ophthalmology, Eugene and Marilyn Glick Eye Institute, Indiana University School of
Refractive error, axial length, and other factors may be more important to consider with angle-closure glaucoma risk, Dr. Cantor said.
The decision to purchase and use certain tools for glaucoma detection based on these kinds of studies should be considered not only in the U.S. but also in Asian countries, said Shan Lin, M.D., professor of ophthalmology, Department of Ophthalmology, University of California, San Francisco. For example, the scanning peripheral anterior chamber depth analyzer for angle-closure glaucoma is more prevalent in Asia, which makes sense when you consider the higher risk of this glaucoma type among Asians, he said.
Although Dr. Rhee believes that glaucoma prevalence in the Asian population is now well established, he thinks this kind of study paves the way for genetic profiling within glaucoma. "In the distant future, we may be able to attribute risk to the presence or absence of certain genetic profiles," he said. Dr. Lin agreed that genetic profiling and research is an area ripe for exploration. He also believes that a closer look at risk in Asian ethnicities that could not be covered in this study would be another future research area.
Although Dr. Lin believes the ethnicity classification method used in the study is a weakness, he said it does not detract from the overall value of the study results. Dr. Stein and co-investigators are conducting research regarding whether racial disparities exist in how eyecare providers care for glaucoma patients.
Editors' note: The physicians have no financial interests related to this article.
Cantor: 317-274-8485, firstname.lastname@example.org
Rhee: 617-573-3670, email@example.com