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Rebekka Heitmar; Ethnic differences or imaging problems: Dual wavelength retinal vessel oximetry in Caucasians and South Asians. Invest. Ophthalmol. Vis. Sci. 2013;54(15):47.
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© ARVO (1962-2015); The Authors (2016-present)
To collect normative oximetric data from healthy Caucasians and South Asians.
Forty healthy volunteers (20 Caucasian and 20 South Asian) underwent non-contact tonometry, digital blood pressure measurements and dual wavelength oximetry. Oximetric images were collected using the Imedos Oximetry Tool, capturing images at 548 and 610 nm simultaneously using a dual wavelength filter. All images were collected with the camera angle set at 30 degrees and the optic nerve head centred. Oximetric data was analysed in a concentric ring around the nerve head.
All subjects were normotensive. There was no difference between Caucasians and Asians in the number and diameter of vessels included for analysis. However, the optical density ratio as well as the oxygen saturation derived from it were significantly different in Caucasians (CA) compared to South Asians (SA) (ODR arteries: CA 0.045 (0.016), SA 0.075 (0.026), p=0.0001; ODR veins: CA 0.147 (0.038), SA 0.200 (0.034), p=0.00005; SO2 arteries: CA 95 (8)%, SA 87 (9)%, p=0.003; SO2 veins: CA 57 (14)%, SA 41 (10)%, p=0.0004).
This data clearly shows differences in the optical density measurements obtained form two ethnic groups. The differences between groups highlights the need of further investigation into the imaging technology in particular the equation to calculate oxygen saturation. The Imedos Oxyimetry Tool automatically implements a diameter and pigmentary correction but this might not be suitable.
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