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R.B. Dinn, A. Harris, L. Kagemann, H.J. Garzozi, S. Kresovsky; A New Image Analysis Technique for the Calculation of Optical Density in Retinal Oximetry . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3616.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Optical density (OD) is defined as log10(1/transmission), with transmission equal to transmitted light/illumination. In the case of reflectance oximetry utilizing an 8 bit digital image (0 = black and 255 = white), the illumination has a level of 255. The purpose of this study is to determine the effect of an improved unconventional pigment insensitive method of optical density calculation on reproducibility in retinal oximetry. Methods: : All procedures were approved by an IRB, and informed consent obtained. Five oximetry images were obtained in 17 normal healthy adults. Images were analyzed using a conventional OD calculation, and an innovative OD calculation; replacing the illumination level of 255 with the average reflectance of tissue surrounding blood vessels. OD, therefore, becomes log10(tissue/blood vessel). The coefficient of variation (CV) was calculated for each OD method, and compared by paired student’s t test. Results: CV of the old and new artery OD calculations were 12.0% and 12.9% respectively (p = 0.76). For the vein, the CVs were 12.6% and 14.7% (p = 0.59). Conclusions: Replacing the 255 constant term with a varying tissue reflectance level does not significantly alter variability in the calculation optical density in retinal oximetry analysis.
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