Protective Role of Axial Length in Diabetic Retinopathy: A Case-Control Study

Background Diabetic retinopathy (DR) is the most common microvascular complication of type 2 diabetes mellitus (T2D) and a leading cause of visual impairment. Axial length (AL) of the eye has been implicated in retinal structure and may influence DR pathogenesis. This study aimed to test the hypothesis that longer ocular AL exerts a protective effect against the development and progression of DR. In addition, it sought to examine secondary associations between AL and demographic or clinical variables, including sex, diabetes duration, insulin use, and presence of diabetic macular edema. Methods A total of 455 adults aged 50-85 years were included, of whom 135 (29.7%) had confirmed T2D. AL was measured using the IOL Master 500, and DR staging was performed through indirect ophthalmoscopy and optical coherence tomography (OCT). Due to non-normal data distribution, non-parametric tests were used (Mann-Whitney U, Kruskal-Wallis, Spearman, Pearson Chi-Square). Results Diabetic patients exhibited significantly lower median AL compared to non-diabetics (23.26 mm vs. 23.50 mm, <i>p</i> = 0.006). Among diabetics, males had longer AL than females (23.37 mm vs. 22.86 mm, <i>p</i> = 0.001). Participants without any signs of DR had significantly greater AL than those with any DR stage (23.63 mm vs. 23.00 mm, <i>p</i> = 0.042). Furthermore, AL varied significantly across DR stages (<i>p</i> = 0.017), with a trend toward shorter length in more advanced stages. Conclusions Longer AL is inversely associated with both the presence and severity of DR. AL may represent a protective anatomical factor and could be considered in the clinical evaluation and risk stratification of patients with T2D.