Diabetic Retinopathy Concentrated in High Poverty Zip Codes

High poverty zip codes in Chicago — those with the highest percentage of households below the federal poverty level (FPL) — are also the locations with the highest rates of diabetic retinopathy, according to a study published in Ophthalmic Epidemiology. They also have the most non-White residents and the highest rates of undiagnosed diabetic eye disease, suggesting a stark health care disparity.

Rising diabetes mellitus rates intensify the burdens of vision loss and health care costs — so identifying best use of resources becomes key, according to researchers. Using the Chicago HealthLNK Data Repository (HDR), Geographic Information System (GIS), and US census data, the researchers charted DR prevalence by zip code. 

The analysis accessed de-identified records for more than 2 million adults 19 to 89 years of age treated during calendar years 2006 to 2012. Of these, 143,790 records (13.2%) listed International Classification of Diseases (ICD-9) codes for diabetes, diabetic neuropathy, or diabetic cataract — and 11,058 (7.7%) included DR or DR sequelae codes.

A significant correlation appeared between rates of poverty and diabetes, Pearson’s correlation coefficient 0.614 (P <.05), as well as connections for higher DR rates with areas that had more families living below the FPL, coefficient 0.333 (P <.05). Investigators found 67 “ideal” zip codes with low relative risk for diabetes and DR, but a higher percentage whose DR was diagnosed. Conversely, the 36 “high risk” zip codes associated with increased poverty exhibited high relative risk of diabetes and retinopathy, although reduced chance for DR to be identified; presumed under-diagnosis after adjusting for race, insurance coverage, sex, and age.

Thus, poverty and probability for DR diagnosis were negatively linked; shown in a Pearson’s correlation coefficient of  -0.638 (P <.05) — residents in poorest neighborhoods were “least likely to be diagnosed” with retinopathy.

In “ideal” areas, only 10.2% of households lived below the FPL compared with the Chicago metro average of 17.9%, but “high-risk” zip codes included 33.0% below FPL. In ideal zip codes, ethnic/racial minority makeup of 32.6% proved lower than 50.5% for the entire metro area, in contrast to high risk areas that included 85.4% who identified as a minority group member.

The researchers suggest that under-diagnosis reflects less access and screening. “By identifying areas where diabetic eye disease is under-diagnosed, it is possible to precisely identify neighborhoods to deploy resources to detect previously undiagnosed diabetic eye disease,” the invesresearcherstigators explain. 

The Centers for Disease Control and Prevention (CDC) has described a 3.2% prevalence of vision-threatening diabetic retinopathy (VTDR) in individuals who are of non-Hispanic White ethnicity and race, compared with 7.3% in Hispanic, and 9.3% in the non-Hispanic Black community. Prior studies report just half, approximately 50% of US residents with diabetes have an eye screening yearly, and 25% to 33% of those in a number of low economic or minority populations are evaluated.

Limiting this investigation is a possible population bias resulting from exclusively HDR-site data. The sample also had a higher number of diabetes cases than the US average, and lower overall DR rate in 2015 CDC numbers. Additionally, expected DR prevalence was established in prior research that assumes all patients with diabetes are screened. A strength is the large database and demonstration of a method to target resources for equitable vision screening.