Three-Dimensional Mapping of Chorioretinal Vascular Oxygen Tension in the Rat

Abstract

An optical section phosphorescence lifetime imaging system was developed for three-dimensional mapping of oxygen tension (P(O2)) in chorioretinal vasculatures. A laser line was projected at an oblique angle and scanned on the retina after intravenous injection of an oxygen-sensitive molecular probe to generate phosphorescence optical section images. An automated software algorithm segmented and combined images from spatially adjacent locations to construct depth-displaced en face retinal images. Intravascular P(O2) was measured by determining the phosphorescence lifetime. Three-dimensional chorioretinal P(O2) maps were generated in rat eyes under varying fractions of inspired oxygen. Under an air-breathing condition, mean P(O2) in the choroid, retinal arteries, capillaries, and veins were 58+/-2 mm Hg, 47+/-2 mm Hg, 44+/-2 mm Hg, and 35+/-2 mm Hg, respectively. The mean arteriovenous P(O2) difference was 12+/-2 mm Hg. With a lower fraction of inspired oxygen, chorioretinal vascular P(O2) and mean arteriovenous P(O2) differences decreased compared with measurements under an air-breathing condition. Retinal venous P(O2) was statistically lower than P(O2) measured in the retinal artery, capillaries, and choroid (P<0.004). Three-dimensional mapping of chorioretinal oxygen tension allowed quantitative P(O2) measurements in large retinal blood vessels and in retinal capillaries. This method has the potential to facilitate better understanding of retinal oxygenation in health and disease.