Abstract
Abstract: :
Purpose: To test the hypothesis that age influences the human retinal oxygenation response (ROR) in healthy subjects and patients with Type 1 diabetes. Methods: MRI was used to measure ROR during a 40 minute hyperoxic inhalation challenge in 7 healthy subjects (age = 41.5 ± 10.4 years) and 10 patients with Type 1 diabetes mellitus (age = 36.7 ± 11.5 years, duration of diabetes = 21.6 ± 12.8 years) who had either background or no retinopathy. Subjects fixated a small point source and refrained from blinking during a 15–s fast low–angle shot (FLASH) image. This sequence was repeated 20–40 times (5–10 min image acquisition) and used to generate high resolution (390 x 390 µm2 in–plane) image sets in which eye movement artifacts were minimized. Image sets were collected sequentially during the hyperoxic inhalation challenge and signal intensity changes in the pre–retinal vitreous were measured. Results: As expected, both groups exhibited an increase in signal intensity in the pre–retinal vitreous. In healthy subjects ROR increased during the initial 5–10 minutes of the hyperoxic challenge and remained essentially constant thereafter. In patients with Type 1 diabetes, ROR continued to increase throughout the duration of the hyperoxic challenge and was significantly supernormal (p < 0.05). In healthy subjects ROR was highly correlated with age (r = 0.889, p < 0.002), but in diabetic patients the effect of age was non–significant (r = 0.292, p = 0.192). Diabetic patients with and, importantly, without retinopathy had ROR that were greater than normal (p > 0.05), but not different from each other (p < 0.05). The duration of diabetes was not significantly correlated with ROR (p > 0.05). Conclusions: The results demonstrate a difference in the dynamics of ROR between healthy subjects and patients with Type 1 diabetes mellitus that occurs prior to the appearance of clinically detectable retinopathy. However, contrary to our hypothesis age influenced ROR in normal subjects but not in patients with Type 1 diabetes. We suspect that both the supernormal ROR in diabetic patients and the elevation in ROR as a function of age in healthy individuals result from a reduction in vascular reactivity. These findings provide further confirmation that the MRI measurement of ROR to a hyperoxic inhalation challenge provides a robust non– invasive and real–time measurement that has potential clinical utility.
Keywords: diabetic retinopathy • aging • ischemia