Early supernormal retinal oxygenation response in patients with diabetes.

PURPOSE To determine whether the human retinal oxygenation response (deltaPO2) to a hyperoxic provocation is abnormal in patients with type I diabetes. METHODS Magnetic resonance imaging (MRI) was used to measure deltaPO2 during 100% oxygen breathing in patients with type I diabetes who had either no clinically detectable retinopathy (n = 5) or mild to moderate background diabetic retinopathy (BDR; n = 5) and in age-matched healthy control subjects (n = 7). RESULTS Both the patients with diabetes and the control subjects exhibited a significant (P < 0.05) increase in the preretinal vitreous signal intensity on changing from room air breathing to oxygen inhalation (i.e., 5 minutes). However, only diabetic patients demonstrated significant (P < 0.05) increases in deltaPO2 between measurements made at 5 minutes of oxygen inhalation and measurements at longer durations of hyperoxia (15, 25, and 35 minutes). Furthermore, deltaPO2 was significantly (P < 0.05) greater in patients with diabetes than in control subjects, but there was no significant difference in deltaPO2 (P > 0.05) between patients with diabetes, with or without retinopathy. Age and deltaPO2 correlated significantly (P < 0.05) in control subjects but not in patients with diabetes. In control subjects, deltaPO2 was relatively uniform panretinally, whereas in the diabetic group, changes in oxygenation response were spatially inhomogeneous. CONCLUSIONS These results demonstrate, for the first time, that MRI deltaPO2 detects a significant supernormal retinal oxygenation response in patients with type I diabetes, even before the appearance of retinopathy. This study raises the possibility of using MRI measurements of deltaPO2 to monitor therapeutic efficacy in human trials.