Investigating Late-Stage Diabetic Retinopathy: A Long-Term Analysis of Vascular Changes in the Streptozotocin-Induced Mouse Model

Diabetic retinopathy (DR) is characterized by microvascular damage and increased vascular permeability in the retina. The investigation of visual outcomes in late-stage DR is limited by challenges of maintaining chronically hyperglycemic mice and most reports are restricted to early-stage DR. In this study, we used carefully managed diabetic mice to longitudinally investigate associations between vascular leakage and visual acuity during early and late-stage DR. Diabetes was induced in C57Bl/6J mice with streptozotocin (STZ) and fluorescence angiography with dual fluorescence (FA-DF) was used to assess retinal vascular leakage dynamics in chronically hyperglycemic mice for 12-months. Retinal vascular leakage was evident 180 days after diabetes induction and before reduced visual acuity, measured using the optokinetic response, and vascular leakage continued to increase during DR progression. Mice were also treated with intravitreal injections of anti-angiogenic aflibercept at late-stage DR, and reduced leakage was reliably measured using FA-DF and was associated with improved visual acuity. Inflammatory and vascular phenotypes were assessed using immunostaining, which revealed significantly lower retinal macrophage and vascular densities and reduced capillary diameter in association with anti-VEGF treatment compared to age-matched diabetic controls. In conclusion, this is the first longitudinal quantification of retinal vascular leakage in early, intermediate, and late stages of DR in the same cohort of mice in a minimally invasive fashion, to demonstrate the associated effect of anti-angiogenic therapy in vivo. Our findings also further confirmed the sensitivity of FA-DF in assessing retinal vascular leakage in conjunction with other functional measures in longitudinal studies in the same animals.