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Alok K. Sahgal, Jean-Claude Mwanza, Sarah Moyer, Bruce Baldwin, Kathleen Gordon, Seema Garg; Determinants Of Retinal Oxygen Saturation In Healthy Subjects. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2164.
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Retinal oximetry is a novel imaging modality that non-invasively measures retinal oxygen saturation. As an emerging technology, little is known about normal oxygen measurements in healthy adults. In this study, we have evaluated a cohort of healthy individuals to obtain normative values and determine which factors influence retinal oxygen saturation (SO2).
Both eyes of 60 healthy subjects from European, African, Hispanic and Asian descent underwent retinal oximetry (Oxymap, Reykjavik, Iceland) and color fundus photography (Carl Zeiss, Dublin, CA). The SO2 values in retinal arterioles (SaO2) and venules (SvO2) were measured in four retinal quadrants: superotemporal, inferotemporal, superonasal, and inferonasal (the optic nerve was used as the center of the retina). The global SO2 was defined as the average of the four quadrant measurements in either arterioles or venules. The correlation between SO2 and age was assessed using simple linear regression. Multivariate regression analysis was performed to determine the association between global SO2 and ethnicity, iris color, age, gender, eye laterality, refraction, history of smoking and arterial hypertension. Only one eye randomly selected per patient was included in the analysis.
There were 15 subjects from each ethnic group. The average age was 41.8±14.1 years. The average global SaO2 was 93.4±3.0% and global SvO2 was 64.3±4.6%. Global SO2 did not differ between ethnic groups in either arterioles (p = 0.72) or venules (p = 0.38). Statistically significant differences in SaO2 and SvO2 were observed between quadrants (both p < 0.001). Linear regression analysis indicated that SO2 decreases with increasing age, but this effect was significant only in subjects older than 50 years for SaO2 (R2 = 0.37, p = 0.004) and SvO2 (R2 = 0.58 , p < 0.001). In multivariate regression analysis, history of systemic hypertension was the only significant determinant of both global SaO2 (β = -1.19, p = 0.027) and global SvO2 (β = -2.37, p = 0.004) and quadrant SaO2 (β = -1.30 to -1.97, all p <0.01) and quadrant SvO2 (β = -2.27 to -3.34, all p < 0.01).
As a first step in evaluating this emerging technology, we have established a preliminary, multi-ethnic normative database in retinal oximetry. We observed significant variation in SO2 among retinal quadrants. Although older people had lower SO2, history of systemic hypertension was the only significant independent predictor of SO2. These factors should be taken into account when translating retinal oximetry measurements into a clinically meaningful interpretation. Future studies will build on these normal values from which to compare retinal oximetry measurements in disease states.
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