The National Eye Institute estimates that 2.2 million adults in the United States who are 40 years of age or older have glaucoma. By 2020, the number of Americans with this disease is expected to reach 3.3 million.1 Given this projected increase in the prevalence of glaucoma, it will be important to identify people affected by this disease and to treat them before their condition progresses. This effort is especially important for Hispanic and black Americans, among whom glaucoma is a leading cause of blindness. Here, I discuss how ethnic-specific data may help us detect early glaucomatous changes in high-risk groups.
WHO IS AT RISK?
Primary open-angle glaucoma affects people of all ages and ethnicities. The Baltimore Eye Survey, a population-based study of ocular disorders supported by the National Eye Institute, showed that approximately one in 50 white Americans had glaucoma by the time they were 70 years old. Other individuals who had a high risk of developing glaucoma in this study included white Americans aged 50 years or older, blacks over 40 years old, and anyone with a family history of glaucoma.2,3 Studies also show that blacks are likely to develop open-angle glaucoma earlier,3 and four to five times more frequently2 than whites. Additionally, glaucoma tends to progress more quickly and is more likely to result in blindness in black versus white patients.2,4
These statistics highlight the importance of aggressively screening black patients for glaucoma and of developing guidelines that can help us assess this group's risk for the disease. Knowing whom to check, when to evaluate them, and what to look for are the first steps in identifying undiagnosed glaucoma and preventing unnecessary vision loss.
IDENTIFYING NORMAL OPTIC NERVES
Recent landmark studies showed that changes in the optic nerve and retinal nerve fiber layer precede visual field loss5 in glaucoma, making it more important than ever for physicians to assess structural parameters in at-risk patients. Because glaucomatous damage manifests differently among various patients, however, clinicians cannot depend on the analysis of a single parameter to diagnose, rule out, or detect the disease's progression. A complete structural evaluation of glaucoma suspects should include imaging of the optic cup, neural rim, and retinal nerve fiber layer.
Interpreting the health of an optic nerve can be complicated, because its appearance can vary among ethnic groups. To determine if a patient's eye is glaucomatous, doctors need ethnic-specific data that describe the parameters of a healthy eye from someone of similar ethnicity.
For example, blacks tend to have larger optic discs and cups than people of European ancestry.2,4 Data from the University of Southern California/Doheny Eye Center's Los Angeles Latino Eye Study (LALES)5 showed that these structures in Hispanics are also typically larger than in whites but are smaller than in blacks.6 A clinician who is not aware of these ethnic differences in the size of the optic disc could diagnose a healthy eye as glaucomatous or fail to identify early structural changes in a glaucomatous eye.
Fortunately, glaucoma specialists now have diagnostic instruments that not only to acquire baseline measurements of the optic disc and retinal nerve fiber layer, but also detect abnormalities in these structure by comparing them against ethnic-specific databases.
Ethnic-Specific Databases
Of the diagnostic instruments used to assess the optic nerve and RNFL in glaucoma patients, only the Heidelberg Retina Tomograph (HRT3; Heidelberg Engineering GmbH, Heidelberg, Germany) allows operators to specify a patient's race and modify the normative data against which his measurements are assessed.
To help clinicians establish whether a given patient's eyes are glaucomatous, Heidelberg Engineering, Inc., has developed Ethnic-Selectable Databases that include normative data for white (Caucasian), Indian (Southeast Asian), and African populations. The company is also currently developing Hispanic and Asian databases.
Heidelberg Engineering built their normative databases by collecting and analyzing data from studies that documented differences in ocular structure within various populations.
Studies have shown that the HRT can detect glaucoma in individuals whose imaging reports from other devices would be considered normal due to a lack of ethnic-specific data. The HRT's Ethnic Selectable Database makes screening glaucoma suspects for early structural changes easier and more efficient, in my opinion. Until we understand why glaucoma occurs more frequently in black than in white populations, we cannot prevent the disease's onset. Early detection with the aid of HRT and other diagnostic imaging devices, however, may help us prevent further visual deterioration in affected patients.
THE LALES
In 1998, I was part of the team from the Wilmer Eye Institute at Johns Hopkins University in Baltimore that included Alfred Sommer, MD, MHS, and Harry Quigley, MD, which documented the unique characteristics of the optic disc in black and white populations.
The results of the Baltimore Eye Survey give us a better understanding of the glaucoma risk factors for African Americans and persons of European descent and the rationale for developing more effective treatments and protocols.
The work of my mentors at the Wilmer Eye Institute on the Baltimore Eye Survey inspired me to undertake a similar study of the Hispanic population in southern California. While I was completing my glaucoma training at the University of Southern California in Los Angeles, I noticed that a large percentage of my Hispanic patients were losing their vision. Because my colleagues and I did not have enough data to determine whether the primary cause of vision loss in this population was diabetes, lens opacity, or glaucoma, we designed the LALES to evaluate the risk factors for glaucoma as well as to develop more effective detection and treatments protocols for people of Hispanic descent.
Supported by a 5-year grant from the National Eye Institute, my colleagues and I set out to evaluate the burden of ocular disease on Hispanics in Los Angeles. We recruited individuals to come to our clinic for a free evaluation by enlisting the help of block captains, local businesses, eye care providers, priests, schools, and senior centers.7
We established the Local Eye Examination Center in a central location within a housing tract and publicized our project by placing signs around the neighborhood. The signs, similar to those used by politicians at election time, became so popular that several people tried to vote for LALES in the election but could not find his name on any ballot!
After we established our neighborhood clinic, we invited people to come in to undergo a series of standard glaucoma tests. The results of the patients' visual field and optic nerve evaluations were first evaluated by a general ophthalmologist and then by two fellowship-trained glaucoma specialists who determined whether the patient had glaucoma. If the glaucoma specialists encountered any questions or discrepancies, they forwarded the data to another ophthalmologist for adjudication.
Data from the LALES showed a high proportion of previously undiagnosed glaucoma (75%) among the study's participants and demonstrated ethnic-specific differences in the structure of their optic nerves. Although these findings are important, we felt the most valuable part of our interaction with the patients occurred after their examination. We took this opportunity to give patients a detailed assessment of their ocular health—one for their primary eye care providers and another written in lay language for them to keep—and spent approximately 15 minutes discussing any problems detected during the examination. We felt that it was important to educate patients about glaucoma, because many of them were not aware of this "silent" disease and did not consider the health of their eyes to be as important as other competing medical needs.
CONCLUSION
Population-based studies such as the Baltimore Eye Survey and the LALES have provided valuable data about ethnic-specific structural differences in the optic nerves of black and Hispanic patients. Data from the LALES have been incorporated into the HRT's progression analysis software, as well as in the normative databases of optical coherence tomographers.
The availability of diagnostic devices incorporating ethnic-specific data has improved our ability to assess the risk of glaucoma in different populations. Risk assessment is a critical aspect of glaucoma management, because our goal is to identify the disease in people before they develop visual loss. Imaging equipment can help us detect patients who need further assessment or treatment, but only if the device can provide accurate, ethnic-specific information.
Rohit Varma, MD, PhD, is the principal investigator of the AIG clinical center at the University of Southern California Doheny Eye Institute, Keck School of Medicine, Los Angeles. He acknowledged no financial interest in the products or companies mentioned herein. Dr. Varma may be reached at (323) 442-6411; rvarma@usc.edu.
