Nonlinear relationship between diabetes mellitus duration and diabetic retinopathy

To investigate the non-linear relationship between diabetes mellitus (DM) duration and the development of diabetic retinopathy (DR). By investigating the association between these variables, our goal is to contribute to the existing knowledge regarding the impact of DM duration on the development and severity of DR. A retrospective cross-sectional study was conducted on 420 patients in the Department of Endocrinology at Guangdong Provincial People's Hospital, who had undergone ophthalmic consultations from December 2017 to November 2018. The analysis of DM duration and DR utilized a generalized additive model to identify both linear and non-linear connections. The threshold effect was determined using a two-piece regression model. The study included a total of 420 patients, with a mean age of 58.7 years. Of these, 56.9% (239/420) were male. The prevalence of DR was 38.33% (161/420). After adjusting for confounding factors, a nonlinear relationship between DM duration and DR was observed, with a turning point at 8 years. On the left side of the turning point, the prevalence increased by 24% per 1-year increase in DM duration (OR: 1.24; 95% CI: 1.11-1.38; P<0.0001). However, no statistically significant differences were found on the right side of the turning point (OR: 1.02; 95% CI: 0.97-1.08; P = 0.4987). Our study identified a non-linear relationship between DM duration and DR in patients. When the DM duration is less than 8 years, a positive correlation exists between DM duration and DR. However, once the DM duration exceeds 8 years, the effect reaches saturation, and no significant correlation is observed.