Purpose Pilot study to demonstrate the clinical feasibility of using hyperspectral computed tomographic spectroscopy (HCTIS) to measure blood oxygen content in human retinal vessels. Methods All procedures were performed under a University of Southern California IRB approved protocol and after obtaining informed consent. Fifty-seven subjects with and without diabetic retinopathy were dilated for standard fundus photography. Fundus photographs and retinal vascular oxygen measurements (oximetry) were made using a custom made HCTIS coupled to a standard fundus camera. Oximetry measurements were made along arteries (Aox) and veins (Vox) within vessel segments that were 1–2 disc diameters from the optic disc. Results For all control subjects (n=45), mean Aox and Vox were 93±7% and 65±5% (p=0.001) respectively. For all diabetic subjects (n=12), mean Aox and Vox were 90±7% and 68±5% (p=0.001) respectively. In subjects with proliferative diabetic retinopathy, Aox was significantly lower and Vox was significantly higher than other groups (85±4% and 71±4% respectively; p=0.04, ANOVA). There was a highly significant difference in the arteriovenous (AV) difference between subjects with proliferative diabetic retinopathy and those in the control group (14% versus 26%; p=0.003). Conclusions HCTIS is a clinically feasible method for measurement and analysis of vascular oxygen content in retinal health and disease. The current study utilizes techniques relevant to oximetry however, the breadth of spectral data available through the HCTIS may be applicable to studying other anatomical and functional features of the retina in health and disease.

PurposeTo study the variation in intravascular oxygen saturation (oximetry) during an acute retinal vein occlusion (RVO) using hyperspectral computed tomographic spectroscopy based oximetry measurements.MethodsThirty rabbits were dilated and anesthetized for experiments. Baseline oximetry measurements were made using a custom-made hyperspectral computed tomographic imaging spectrometer coupled to a fundus camera. RVO were induced using argon green laser following an intravenous injection of Rose Bengal. RVO induction was confirmed by fluorescein angiography. Retinal oximetry measurements were repeated in arterial and venous branches one hour after RVO induction and up to 4 weeks afterwards. Comparison of retinal oximetry before and after vein occlusion was made using the Student T-test.ResultsOne hour after RVO induction, we observed statistically significant reductions in the intravascular oxygen saturation in temporal retinal arteries (85.1±6.1% vs. 80.6±6.6%; p<0.0001) and veins (71.4±5.5% vs. 64.0±4.7%; p<0.0001). This decrease was reversible in animals that spontaneously recannulated the vein occlusion. There were no statistically significant differences in oxygen saturation in the nasal control arteries and veins before and after temporal vein RVO induction.ConclusionsWe demonstrate, for the first time, acute changes in the intravascular oxygen content of retinal vessels 1 hour after RVO. These changes are reversible upon spontaneous recannulation of retinal vessels. This study demonstrates that hyperspectral computer tomographic spectroscopy based oximetry can detect physiological variations in intravascular retinal oxygen saturation. The study also provides the first qualitative and quantitative evidence of the variation in retinal vascular oxygen content directly attributable to an acute retinal vein occlusion.