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B. L. Petrig, D. A. VanNasdale, A. E. Elsner, B. P. Haggerty, B. D. Hansel, M. Miura, A. Weber; Polarimetric Imaging of Retinal Arteries and Veins in Diabetic Patients and Age-Matched Normals. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3439.
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To quantify retinal blood vessel contrast in diabetic patients imaged with depolarized vs. confocal imaging techniques, and to compare this contrast in arteries and veins of diabetics and age-matched controls.
Twenty-seven patients with diabetic mellitus and retinal status ranging from no retinopathy to non-proliferative diabetic retinopathy were selected. Images were acquired from the posterior pole using a scanning laser polarimeter (GDx, LDT) that is designed to measure linear birefringence of the retina, illuminating 15 x 15 deg of retina at 780 nm with 20 different input polarizations. Light returning from the eye passes through a polarizing beam splitter and then is digitized at 2 detectors, one parallel to the input polarization and the other crossed, resulting in images with varying polarization. Removing the modulation with input polarization angle at the crossed detector provides an estimate of the depolarized light. Vessel profiles were analyzed 5 degrees from the optic nerve head center, for one superior temporal retinal artery and vein pair per patient in the same location in each image (depolarized and confocal). Images from age-matched controls were obtained and analyzed in the same way.
Average Michelson contrast of all retinal vessels in the depolarized light images was excellent, 0.45 and 0.53 in arteries and veins, respectively. Average contrasts were significantly higher for depolarized than for confocal images (p<0 .0001), which were 0.33 and 0.43 for arteries and veins, respectively. Diabetics had generally lower contrasts than their age-matched controls (p<0.036). Average Michelson contrast was greater for veins than for arteries (p<0.0001), as expected.
Central reflections in the average images not only decrease the contrast but also alter the shape of the vessel profile. These results demonstrate the potential for near infrared imaging of blood vessels in diabetic retinopathy and improved retinal vessel computations.
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