Abstract
Purpose:
To quantitatively assess retinal vasculature integrity in a novel diurnal rodent model of type 2 diabetes, the Nile grass rat (arvicanthis niloticus).
Methods:
Three groups were studied with fluorescein angiography (Micron III; Phoenix Research Laboratories) at 6, 12, and 18 months of age. Group 1 were fed a low energy diet (2.91kcal/g; Mazuri Chinchilla) that maintained normoglycemia (<5.0mmol/L fasted blood glucose) at all ages studied. Group 2 were fed standard rodent lab chow (3.52kcal/g; Prolab 2000) and developed hyperglycemia; animals that did not become hyperglycemic fell into group 3. Under anesthesia and mydriasis, images from both eyes were acquired in order to quantify vessel caliber and number at a fixed eccentricity (0.5-1 times the optic disc diameter).
Results:
For group 1, the total vessel number, sum of vessel caliber and optic disk diameter did not vary with age (total vessel number: 13±1, 11.6±1 and 12.3±0.4, sum of vessel caliber: 486.6±11.9µm, 449.5±28µm and 468.6±19.4µm, optic disk diameter: 200.6±1µm, 210±12.8µm and 226.9±2.6µm at 6, 12 and 18 months respectively). When compared to group 1, animals from group 2 had higher values for all 3 outcome measures. Total vessel number: 13, 14.3±1.3 and 17±1, sum of vessel caliber: 504.1±10.3µm, 576.2±41µm and 655.6±23µm, optic disc diameter: 234±15.3, 237.4±21 and 272.2±22.6µm at 6, 12 and 18 months respectively. Nile rats fell in group 3 only when aged 6 and 12 months (standard chow diet induced hyperglycemia at a rate of 100% by the age of 18 months); normoglycemic animals had similar values to group 1 for all 3 outcome mesures: total vessel number of 12.5±1.2 and 13.0±0.7; sum of vessel caliber of 511.3±34.7µm and 486.9±43.3µm; optic disk diameter of 211.2±9.5µm and 219.5±14.3µm at 6 and 12 months respectively.
Conclusions:
Our results indicate that over the course of 6 to 18 months of age, hyperglycemic Nile grass rats develop a vascular retinopathy modeling features that typify the protracted development of diabetic retinopathy in humans afflicted with type 2 diabetes.