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Maziyar M Khansari, Michael Robert Tan, Mahnaz Shahidi; An image analysis method for conjunctival microvascular network oximetry. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5934.
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© ARVO (1962-2015); The Authors (2016-present)
Assessment of oxygen saturation of microvascular network provides knowledge of tissue oxygenation. The purpose of this study is to report a method to perform oximetry in the conjunctival microvascular network.
Dual wavelength conjunctival microvasculature imaging was performed in 5 healthy subjects. Conjunctival images were acquired at 440 nm (oxygen sensitive) and 570 nm (oxygen insensitive). Pulse oximetry was performed to determine systemic arterial oxygen saturation (SO2). Images were analyzed using a dedicated image analysis algorithm. Microvessels within the network were automatically segmented for determining optical density (OD), defined as the log ratio of intensity outside to intensity inside of each vessel segment. Optical density ratio (ODR) was computed as the ratio of OD440 to OD570. Repeatability of ODR measurements was determined by coefficient of variation of 2-3 repeated measurements in each vessel segment. Inter-regional variability of ODR was assessed by coefficient of variation of measurements obtained in 3-4 different conjunctival regions.
Mean age of subjects was 34 ± 12 years (range, 26 - 52 years). ODR repeatability was assessed in 15 vessels with diameters that ranged between 16 and 43 microns (mean, 25 ± 7 microns). ODR measurement repeatability was on average 13% (range, 6% - 23%). Mean ODR was inversely correlated with systemic SO2 (R = 0.98; p = 0.003; N=5). In 4 of these subjects, inter-regional variability was assessed from 57 vessel segments in 14 conjunctival regions. Inter-regional variability of ODR was on average 12% (range, 6% - 18%). Mean vessel diameter and ODR in these regions were between 21 and 23 microns (mean, 22 ± 1 microns) and between 0.82 and 0.97 (mean, 0.88 ± 0.07), respectively. There was not a significant linear relationship between ODR and vessel diameter (R = 0.3; p = 0.3; N=14).
In conjunctival microvascular network of healthy subjects, ODR repeatability and inter-regional variations were comparable. Future studies are needed to establish the potential of this method for evaluation of systemic conditions.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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