Automatic retinal oximetry.
OBJECTIVE
To measure hemoglobin oxygen saturation (SO(2)) in retinal vessels and to test the reproducibility and sensitivity of an automatic spectrophotometric oximeter.


METHODS
Specialized software automatically identifies the retinal blood vessels on fundus images, which are obtained with four different wavelengths of light. The software calculates optical density ratios (ODRs) for each vessel. The reproducibility was evaluated by analyzing five repeated measurements of the same vessels. A linear relationship between SO(2) and ODR was assumed and a linear model derived. After calibration, reproducibility and sensitivity were calculated in terms of SO(2). Systemic hyperoxia (n = 16) was induced in healthy volunteers by changing the O(2) concentration in inhaled air from 21% to 100%.


RESULTS
The automatic software enhanced reproducibility, and the mean SD for repeated measurements was 3.7% for arterioles and 5.3% venules, in terms of percentage of SO(2) (five repeats, 10 individuals). The model derived for calibration was SO(2) = 125 - 142 . ODR. The arterial SO(2) measured 96% +/- 9% (mean +/- SD) during normoxia and 101% +/- 8% during hyperoxia (n = 16). The difference between normoxia and hyperoxia was significant (P = 0.0027, paired t-test). Corresponding numbers for venules were 55% +/- 14% and 78% +/- 15% (P < 0.0001). SO(2) is displayed as a pseudocolor map drawn on fundus images.


CONCLUSIONS
The retinal oximeter is reliable, easy to use, and sensitive to changes in SO(2) when concentration of O(2) in inhaled air is changed.
Hardarson
Sveinn Hakon
SH
Department of Ophthalmology, University of Iceland, National Univbersity Hospital, Reykjavik, Iceland.
Harris
Alon
A
Karlsson
Robert Arnar
RA
Halldorsson
Gisli Hreinn
GH
Kagemann
Larry
L
Rechtman
Ehud
E
Zoega
Gunnar Már
GM
Eysteinsson
Thor
T
Benediktsson
Jon Atli
JA
Thorsteinsson
Adalbjorn
A
Jensen
Peter Koch
PK
Beach
James
J
Stefánsson
Einar
E
D006801:Humans; D018496:Hyperoxia / Q000378:metabolism; D010092:Oximetry / Q000295:instrumentation*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology; D010108:Oxyhemoglobins / Q000378:metabolism; D015203:Reproducibility of Results; D012161:Retinal Artery / Q000378:metabolism*; D012169:Retinal Vein / Q000378:metabolism*; D012680:Sensitivity and Specificity
D010108:Oxyhemoglobins; D010100:Oxygen