The Human Retinal Oxygenation Response: Measurements in Normals and Patients with Diabetes.

Abstract

Abstract: : Purpose: To determine the human retinal oxygenation response to a hyperoxic inhalation challenge in healthy individuals and to quantitatively compare this with the retinal oxygenation response of diabetic patients. Methods:MRI was used to measure the retinal oxygenation response to a hyperoxic inhalation challenge in 6 healthy subjects (controls, 42–55 years of age) and 4 patients with Type 1 diabetes mellitus (21–51 years of age) who had either mild non–proliferative or no retinopathy. Subjects were asked to fixate a small point source and to refrain from blinking during a 12–s fast low–angle shot (FLASH) image, and to blink if necessary during a 3–s rest period. 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. Two image sets were collected while breathing room air and four image sets were sequentially collected during the hyperoxic inhalation challenge (breathing O₂). Signal intensity changes in the pre–retinal vitreous during the hyperoxic inhalation challenge were measured. Results: Analyzable MRI image sets were obtained from each of the 10 subjects. During the hyperoxic inhalation challenge both groups exhibited an increase in signal intensity in the pre–retinal vitreous. However, during the hyperoxic challenge signal intensity increased more rapidly in the diabetic patients than in the controls. Consequently, following 35 min of hyperoxic challenge there was a statistically significant difference (p < 0.0001, based upon a generalized estimating equation approach) in signal intensity between the two groups. Conclusions: The MRI measurement of the retinal oxygenation response to a hyperoxic inhalation challenge provides a non– invasive, real–time, measurement of human retinal oxygenation. These initial results suggest, for the first time, that there is a significant difference in the dynamics of the retinal oxygenation response between healthy individuals and patients with Type 1 diabetes mellitus.

Keywords: diabetic retinopathy • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • clinical research methodology