Retinal Vascular Oxygen Saturation in Diabetic Rats: A Study using Hyperspectral Computed Tomographic Imaging Spectroscopy

Abstract

 

Purpose

 

To assess changes in retinal vascular oxygen concentration in a diabetic rat model using hyperspectral computed tomographic imaging spectroscopy (HCTIS).

 

Methods

 

Nine brown Norway rats were anesthetized and dilated for retinal imaging. Six rats were injected with 65mg/kg of Streptozotocin (STZ) to induce hyperglycemia, and 3 rats with 0.9% saline control. Blood glucose levels were measured after a 12 hour fast using Accu-Chek Aviva Plus glucometer (Roche Inc). Baseline oximetry measurements and fundus photographs were taken in both eyes of each rat. HCTIS oximetry measurements were taken every 2 weeks after STZ injection for up to 2 months. The same vessel areas were selected for analysis at each time point. Fundus photos and FA were repeated at 2 months. Comparison of retinal arterial (A_ox) and venous (V_ox) oxygen saturation levels were made at each time point using the Student T-test.

 

Results

 

All experimental rats developed and maintained hyperglycemia (mean 410±41 mg/dl), and all control rats remained normoglycemic (mean 124±24 mg/dl) over the 2 months of the study. For control rats (n=3) mean A_ox was 95±1%, 100±4%, 97±6%, 102±5%, and 100±7% and mean V_ox was 90±4%, 88±3%, 86±3%, 87±2%, and 87±5% at baseline, 2, 4, 6, and 8 weeks. For experimental rats (n=6) mean A_ox was 91±2%, 94±4%, 91±4%, 94±3%, 94±5% and mean V_ox was 89±3%, 90±4%, 88±2%, 86±3%, 85±3% at baseline, 2, 4, 6, and 8 weeks. There were no significant differences between control and experimental A_ox and V_ox for each time point. The arteriovenous difference at each time point also showed no clear trends. V_ox measurements in the diabetic rats showed a decreasing V_ox trend over time when compared with baseline (p=0.76, 0.57, 0.17, 0.07).

 

Conclusions

 

There was a trend towards decreasing V_ox over 2 months time in experimentally induced diabetic rats but this was not statistically significant. There were no significant differences in A_ox and V_ox in rats with experimentally induced diabetes versus controls. HCTIS is a useful method for measuring retinal vascular oxygen content in the rat model.