Abstract
The purpose of this study was to develop and validate a tool for the measurement of retinal oxygen saturation using a conventional fundus camera–based nonsimultaneous imaging technique. Retinal oximetry setup comprising a conventional Zeiss FF450IR fundus camera, dual wavelength band-pass filters of wavelengths 570 and 600 nm were used. Image analysis was performed using MATLAB R2013b. All the study participants underwent comprehensive eye examination, fundus examination, complete hemogram analysis, and evaluation of systemic hemodynamics. Fundus images were captured by a nonsimultaneous retinal oximetry. A total of 45 subjects were included in the analysis. Median age of the subjects was 21 years ranging from 19 to 34 years. The median retinal arteriolar and venular oxygen saturation was 94.7% and 55.8%. Comparison of retinal oxygen saturation between three visits showed no statistically significant difference for both arteriolar (p = 0.33)and venular oxygen saturation (p = 0.79). Intraclass correlation coefficients for test–retest, short-term, and day-to-day repeatability were 0.84, 0.90, and 0.86 for arteriolar oxygen saturation and 0.92, 0.98, and 0.98 for retinal venular oxygen saturation. Oxygen saturation in retinal arteriolar and venular blood vessels can be measured by nonsimultaneous image acquisition technique using a conventional fundus camera with good repeatability.
Highlights
In recent years, the use of these oximeters in research has increased, they are not utilized in clinical practice
Zeiss FF450IR (Carl Zeiss Meditech) fundus camera with Zeiss ZK-5 camera back was used for capturing the retinal images using oxyhemoglobin sensitive and oxyhemoglobin insensitive wavelengths, the wavelengths of filters that were used for the oxyhemoglobin sensitive and oxyhemoglobin insensitive wavelengths were 600 and 570 nm with a bandwidth of 10 nm each[8] (Fig. 1); The individual has given written informed consent to publish his photograph in the manuscript
An algorithm was written using MATLAB R2013b to calculate the optical density ratio of the blood vessels at two different wavelengths, as it is linearly proportional to the oxygen saturation
Summary
The use of these oximeters in research has increased, they are not utilized in clinical practice This is probably because of the fact that these measurements are more for academic interest and the equipment are stand-alone devices used only for this purpose and need change in the hardware part of the imaging system. These are usually camera specific and as they are based on the simultaneous acquisition of retinal image with two wavelength filters, they need changes in the camera, which increases the cost; again limiting their clinical use. The aim of this study was to develop a method for measuring oxygen saturation in the retinal vessels using the existing retinal camera, Zeiss FF450IR (Carl Zeiss Meditech, Germany); to elucidate the test–retest, day-to-day, and short-term variability of the system; and to report the results of the pilot study in using this customized device
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