Non-invasive measurement of retinal permeability in a diabetic rat model.

OBJECTIVE: The gold standard for measuring blood-retinal barrier permeability is the Evans blue assay. However, this technique has limitations in vivo, including non-specific tissue binding and toxicity. This study describes a non-toxic, high throughput and cost effective alternative technique that minimizes animal usage. METHODS: Sodium fluorescein fundus angiography was performed in non- and diabetic Brown Norway rats on days 0, 7, 14, 21 and 28. Sodium fluorescein intensity in the retinal interstitium and a main retinal vessel were measured over time. The intensity gradients were used to quantify retinal vascular permeability. Post study eyes were fixed, dissected and stained (isolectin B4) to measure required parameters for permeability quantification including: Total vessel length per retinal volume, radius and thickness. RESULTS: In the non-diabetic cohort retinal permeability remained constant over the 28-day study period. However, in the diabetic cohort there was a significant and progressive increase in retinal permeability from day 14 to 28 (p<0.01, p<0.001, p<0.0001). CONCLUSIONS: This novel imaging methodology in combination with mathematical quantification allows retinal permeability to be non-invasively and accurately measured at multiple time points in the same animal. In addition, this technique is a non-toxic, rapid, sensitive and cost-effective alternative to the Evans blue assay.