Noninvasive Assessment of Retinal Vascular Oxygen Content Among Normal and Diabetic Human Subjects

Abstract

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.

Retinal Oxygen Saturation in Patients with Primary Open-angle Glaucoma Using a Non-flash Hypespectral Camera

“…[1][2][3] Despite several limitations including media clarity, scatter, and pigmentation, 4,5 the assessment of oxygen saturation in the retinal vessels could be a significant advancement in the understanding of ocular diseases. Hyperspectral imaging combines spectroscopy with digital imaging and the clinical utility and benefits of this technique in measuring blood oximetry, using the different spectral characteristics of oxygenated (HbO 2 ) versus deoxygenated hemoglobin in health and disease has been described in previous research.…”

Imaging of Hypoxia in Retinal Vascular Disease

“…A limited number of studies have utilized full spectral imaging to examine changes in oxygen saturation in diabetic retinopathy. Kashani et al used HCTIS to examine changes in S a O 2 and S v O 2 between healthy individuals and patients with DR and determined that S a O 2 was significantly lower, while S v O 2 was significantly higher in patients with proliferative DR [91]. This was confirmed by a significant difference in the arteriovenous difference between the two groups [91].…”

“…Whereas this process originally took several seconds due to sequential acquisition of many single-dimension images, new technology allows for enough images to be taken to cover a 15 degree field with good spatial resolution in only a few milliseconds [90]. Today, HSI has been further developed into hyperspectral computed tomographic imaging spectroscopy (HCTIS), which in addition to giving detailed oxygen saturation maps, can give information about changes in the retina such as lesions, perfusion, and pigment density [90,91].…”

Hyperspectral imaging of retinal microvascular anatomy

“…Most recently, hyperspectral studies in vivo in patients demonstrated significant variations in the retinal vascular oxygen content among normal subjects and patients with diabetic retinopathy; the study also demonstrated for the first time that HCTIS is a clinically feasible method for assessing intravascular oxygen content in humans [38] . Previously, the HCTIS oximetry method had been validated in animal models [14,39,40] .…”