The linear association between estimated glomerular filtration rate and diabetic retinopathy: a cross-sectional study

Diabetic retinopathy (DR) is the predominant microvascular complication of diabetes and the main cause of preventable blindness in working-age adults. Because the retina and kidney share similar microvascular architecture, renal dysfunction-routinely expressed as the estimated glomerular filtration rate (eGFR)-is biologically plausible as a marker of DR risk. However, the relationship between eGFR and DR remains controversial. This study aimed to investigate the association between eGFR and DR prevalence in diabetic patients with type 2 diabetes mellitus. This study represents a secondary analysis of data derived from a cross-sectional study. We included 2001 adults with diabetes mellitus (858 men and 1143 women; mean age 64.0 ± 11.3 years) who attended the internal-medicine outpatient clinics of two hospitals in southern Taiwan between April 2002 and November 2004. Demographic and clinical variables were recorded, and eGFR was calculated using the simplified MDRD equation. The association between eGFR and DR was examined with multivariable logistic regression, adjusting for potential confounders. To explore potential non-linear relationships, we further applied a generalized additive model (GAM) with smooth-spline fitting. Higher eGFR was inversely associated with the odds of DR across progressively adjusted models. When modeled as a continuous variable, higher eGFR was linked to lower DR odds in Model 1 (OR 0.88; 95% CI 0.83-0.92; P < 0.0001), Model 2 (OR 0.90; 95% CI 0.85-0.95; P < 0.0001), and remained significant after full adjustment in Model 3 (OR 0.92; 95% CI 0.87-0.98; P = 0.0056), indicating a robust inverse association. Compared with the lowest eGFR tertile (15.36-60.50 mL/min/1.73 m²), the highest tertile (76.68-141.22 mL/min/1.73 m²) showed a 30% lower risk of DR (adjusted OR 0.70, 95% CI 0.50-0.90). Smooth-spline analysis confirmed a linear inverse relationship, and no significant effect modification was observed across subgroups of age, sex, BMI, blood pressure, glycaemic control or cardiovascular comorbidities. This cross-sectional analysis demonstrates a clear dose-response pattern: each incremental increase in estimated glomerular filtration rate (eGFR) is associated with a proportional reduction in the likelihood of diabetic retinopathy among adults with type 2 diabetes mellitus. Future work should dissect the shared microvascular pathways linking the kidney and retina and determine whether interventions that preserve renal function can translate into meaningful reductions in retinopathy risk.