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Diabetic Retinopathy on the Rise

Posted: Wednesday, June 17, 2009

After two decades on the rise, retinopathy now affects more than a third of all diabetes patients, according to the latest nationally representative estimate.

The prevalence of the condition appeared to increase across racial and ethnic groups between the 1988-1994 and 2005-2006 iterations of the National Health and Nutrition Examination Survey, Jinan Saaddine, M.D., M.P.H., of the CDC, and colleagues found.

Non-Hispanic blacks had the highest prevalence of diabetic retinopathy, and the greatest increase, the researchers reported here at the American Diabetes Association meeting.

"It could be that we're not doing a good job controlling people with diabetes," Dr. Saaddine said, emphasizing the need for good glycemic and blood pressure management alongside diabetes prevention efforts.

"All the studies have shown that control of these two risk factors will delay the progression of diabetic retinopathy and the vision loss related to it," she noted.

But she cautioned that comparison between surveys was complicated by some differences in methodology and by the small sample size of the latest survey.

NHANES III from 1988-1994 used only one photo of one eye to diagnose retinopathy whereas the latest NHANES used two 45° color fundus images of each eye taken on a nonmydriatic digital camera.

The analysis of the 2005-2006 survey included interviews and examinations with gradable fundus photos from 349 participants age 40 and older who had self-reported diabetes.

Among them, the overall diabetic retinopathy prevalence was 34.3%. Ethnic and racial breakdowns from the two surveys were as follows:

    * Non-Hispanic whites: 30.8% prevalence (95% CI 22.6 to 40.5), compared with 18.2% in NHANES III (95% CI 12.9 to 23.6)
    * Non-Hispanic blacks: 47.8% (95% CI 35.7 to 60.2), compared with 26.5% in NHANES III (95% CI 19.3 to 33.6)
    * Mexican Americans: 40.0% (95% CI 25.9 to 56.0) compared with 33.4% in NHANES III (95% CI 26.7 to 40.1)

The prevalence of nonproliferative diabetic retinopathy was 20%, with a 10% prevalence of moderate-to-severe cases, classified using the Airlie House system.

Proliferative diabetic retinopathy prevalence was just 3%, while, late stage retinal damage -- vision-threatening diabetic retinopathy -- was 6%.

One of the major risk factors was duration of diabetes. The prevalence rose from about 10% for those who had been diagnosed for less than five years, to 39% for those diagnosed for five to 14 years, all the way to 70% for those diagnosed for more than 15 years.

Every five additional years of diabetes duration increased the odds for diabetic retinopathy by 60% (OR 1.60, 95% CI 1.02 to 2.5).

Other risk factors for diabetic retinopathy in the multivariate analysis included:

    * Male sex (OR 2.1, 95% CI 1.2 to 4.0)
    * Higher severity of diabetes, indicated by use of insulin and oral diabetes treatments versus pills alone (OR 2.5, 95% CI 1.1 to 5.7) or use of pills alone versus no treatment (OR 5.0, 95% CI 0.7 to 33.3)
    * Higher average systolic blood pressure (OR 1.3 per 10 mm Hg, 95% CI 1.1 to 1.5)
    * Higher hemoglobin A1c (OR 1.4 per 1%, 95% CI 1.1 to 1.7)

Dr. Saaddine mentions that, while these risk factors showed no surprises, this suggested that "the ones that we discovered as risk factors 20 years ago, they're still risk factors and they're not really controlled well."

Prevalence also tended to be higher among minority racial and ethnic groups in the univariate analysis, although this was not significant, most likely because of the small sample size, Dr. Saaddine said.

"Screening for diabetic retinopathy is efficacious and cost-effective, but there has been suboptimal implementation," she said.

Practice Pearls:

Explain to interested patients that high blood glucose levels from poorly controlled diabetes can cause damage to the retinas, eventually leading to vision loss.

Note that this study was published as an abstract and presented orally at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

Source: Diabetes In Control: Saaddine JB, et al "Prevalence of diabetic retinopathy in the United States: National Health and Nutrition Examination Survey 2005-2006" ADA 2009; Abstract OR 382.