Nearly 3 in 10 Americans with diabetes over the age of 40 suffer from vision impairment caused by diabetic retinopathy, and about 4.4% have a form of the condition so severe it threatens their eyesight, researchers said Tuesday.
The overall figure is more than 10 percentage points lower than the proportion observed in earlier studies, but it is not clear whether the difference represents improvements brought about by better control of blood sugar levels or errors in the previous research, a team from the Centers for Disease Control and Prevention, the National Eye Institute and the University of Wisconsin reported in the Journal of the American Medical Assn.
Dr. David M. Kendall, chief scientific and medical officer of the American Diabetes Assn., cautioned that comparing the results of such studies “is probably challenging.” Even if the prevalence of retinopathy has declined by a small amount, “the absolute burden continues to be substantial because the total number of people with diabetes continues to grow.”
An estimated 23.6 million Americans have diabetes, and diabetic retinopathy is the leading cause of blindness among adults in the United States. With diabetics living longer because of better care, the number of cases can be expected to grow even further.
The problem is especially severe among African Americans and Latinos. About 38.8% of black diabetics have retinopathy and 9.3% have a vision-threatening form; among Latino diabetics, 34% have retinopathy and 7.3% have the severe form.
Researchers suspect that the higher prevalence in those groups is due to impaired access to eye examinations and care, as well as poorer care for their diabetes. The findings support the need for regular eye exams and for aggressive treatment of the underlying diabetes, said Dr. Spyros Mezitis, an endocrinologist at Lenox Hill Hospital in New York City who was not involved in the study.
The earlier data about retinopathy, produced in 2004, analyzed the combined results of eight studies conducted in the 1980s and 1990s that were mostly regional. That report found that about 40% of diabetic Americans had retinopathy and about 8% had the severe form.
For the new study, Dr. Xinzhi Zhang of the CDC’s National Center for Chronic Disease Prevention and Health Promotion and colleagues used data gathered from 1,006 participants between 2005 and 2008. Photographs of each eye of those who had been diagnosed with diabetes were analyzed to determine the presence of retinopathy.
Their results were then extrapolated to the population at large to yield a national prevalence.
The study had several limitations, the authors said. It did not include people who were institutionalized, such as in nursing homes, and thus might under-represent the true prevalence. Also, eye photos were not available for all the diabetics.
Finally, the researchers were not able to distinguish between people with Type 2 diabetes and those with Type 1, which is typically diagnosed during childhood. The latter group would be expected to have a much higher incidence of retinopathy because they have had their diabetes much longer.