Evaluation of the optic nerve in patients with diabetic retinopathy using shear-wave elastography and superb microvascular imaging

Objective: To quantitatively assess optic nerve microcirculation—via Superb Micro-vascular Imaging–Vascular Index (SMI-VI)—and tissue stiffness—via Shear-Wave Elastography (SWE)—in patients with diabetic retinopathy (DR), delineating changes across disease stages and differences from controls. We also aimed to evaluate the feasibility of standardized measurement protocols and their potential contribution to clinical decision-making. Materials and Methods: This prospective study was conducted jointly by the Departments of Radiology and Ophthalmology at Selçuk University Faculty of Medicine Hospital between June 2022 and May 2025. The cohort comprised adults stratified into control and DR-stage groups. In total, 101 participants were included (67 with diabetes; 34 controls). VI was measured on SMI using a manual ROI placed over an approximately 3-mm posterior optic nerve segment; SWE was performed in the same segment using a 1-mm² ROI, averaging three acquisitions. All examinations were performed by a single operator on a Toshiba Aplio 500 ultrasonography system (Canon Medical Systems, Tokyo, Japan) with a 14-MHz linear probe. Statistical analyses included normality (Shapiro–Wilk), homogeneity of variance (Levene), independent-samples t test, one-way ANOVA/Welch ANOVA, and appropriate post-hoc tests (Tukey HSD, Games–Howell). Results: Mean VI values in controls were 32.0 ± 2.7 (left) and 32.8 ± 3.1 (right), whereas in all diabetic groups they were 26.5 ± 5.9 (left) and 27.8 ± 5.0 (right) (all comparisons p < 0.001). Welch ANOVA for VI was significant across DR stages (left: F(5, 28.30)=11.90; right: F(5, 29.60)=9.92; p < 0.001), with post-hoc analyses showing pronounced reductions particularly in PDR. VI distributions trended lower with advancing disease. For SWE, control means were 1.62 ± 0.34 m/s (left) and 1.64 ± 0.33 m/s (right), versus 2.09 ± 0.39 m/s and 2.07 ± 0.39 m/s, respectively, in the diabetic cohort. Between-group differences were significant for both eyes (left: t(99)=−5.466; p < 0.001; right: t(99)=−5.999; p < 0.001). Stage-wise comparisons in both eyes indicated a consistent increase in stiffness in mid-to-advanced DR relative to controls. Conclusion: With increasing DR severity, VI—reflecting optic nerve microcirculation—decreases, while SWE—reflecting tissue stiffness—increases. VI and SWE may serve as complementary, noninvasive biomarkers that support DR staging and inform clinical decision-making. Keywords: Diabetic retinopathy; Optic nerve; Optic nerve microcirculation; Shear-wave elastography; Superb Microvascular Imaging; Vascular index