ADAGES finds racial differences in visual function of healthy eyes

June 1, 2008

An analysis of results from visual field tests performed in persons enrolled in the African Descent And Glaucoma Evaluation Study shows that in "healthy eyes," visual function is worse in persons of African descent compared with those of European descent, even though it still is within normal ranges.

Key Points

Washington, DC-Analyses of baseline data collected in the African Descent And Glaucoma Evaluation Study (ADAGES) show that significant ancestry-related differences in visual field test results exist among persons with healthy eyes. In three separate tests, even though results are within normal ranges, people of African descent had significantly worse visual function than those of European descent, reported Pamela A. Sample, PhD, at the annual meeting of the American Glaucoma Society.

"Our data suggest that early visual loss may be present in the African descent population, but they also may point to the need for ancestry-specific normative databases for visual field testing. We hope that longitudinal follow-up will provide us with more insight into these issues," said Dr. Sample, director of clinical vision research, Hamilton Glaucoma Center, Department of Ophthalmology, University of California, San Diego. She also is a principal investigator for ADAGES.

Previous population-based studies have provided information on race-related epidemiologic differences in glaucoma. Those studies estimate that, compared with persons of European descent, individuals of African descent have an approximate five-fold greater prevalence of glaucoma, develop the disease about 10 years earlier, have disease that progresses more rapidly, and are more likely to develop irreversible blindness. Previous research also has shown differences in optic disc size and vertical and horizontal cup-to-disc ratios when comparing groups of healthy eyes among persons of African versus European descent.

ADAGES is believed to be the first prospective, longitudinal observational study of primary open-angle glaucoma in persons of African descent. Sponsored by the National Eye Institute, it is being conducted at three investigational sites and recently completed enrollment of an adult population (aged at least 18 years) encompassing a full spectrum of participants, from those with healthy eyes to those with advanced glaucoma. The study is evaluating the relationship between structural changes and glaucomatous vision loss and is the first study in which African descent and European descent populations are matched for quality and access to care.

ADAGES has enrolled 1,222 subjects. The analyses Dr. Sample presented were based on data from one eye of 150 individuals of African descent and 118 individuals of European descent with healthy eyes. All had normal-appearing optic discs bilaterally on stereophotography along with no evidence of other ocular disease or any history of elevated IOP or glaucoma medication use. All persons included in the analysis had two reliable tests on standard automated perimetry using the Swedish Interactive Thresholding Algorithm, short-wavelength automated perimetry, and frequency-doubling technology 24-2 (Humphrey Matrix, Carl Zeiss Meditec) over a 3-month period.

"The visual field results were not used for classification purposes, so we had a fair comparison among the three tests, and we only used the data from the second test for each method to minimize any learning effect impact," noted Dr. Sample.

The African and European descent groups were comparable with respect to age, visual acuity, family history of glaucoma, and proportions of persons with diabetes and heart disease, although the incidence of systemic hypertension was nearly twice as high and significantly different in the African descent group compared with the European descent group.

Results

For the three visual function tests, the results of the individual participants were mostly well within the normal range. Significant differences, however, were found between racial groups in all three visual function tests in the mean deviation, pattern standard deviation, and number of pattern deviation points affected.

"In spite of the fact that all other measures made on these individuals indicate they are healthy eyes, there appear to be some outliers who are driving some of the results," said Dr. Sample. "However, even when these eyes are excluded, differences in visual function tests remain between the groups and are still statistically significant."

The baseline data for the study have been locked down, and the study design and baseline findings will be reported in a series of papers planned for submission this spring and early summer.