Retinal oximetry based on nonsimultaneous image acquisition using a conventional fundus camera

To measure the retinal arteriole and venule oxygen saturation (SO ₂) using a conventional fundus camera, retinal oximetry based on nonsimultaneous image acquisition was developed and evaluated. Two retinal images were sequentially acquired using a conventional fundus camera with two bandpass filters (568 nm: isobestic, 600 nm: nonisobestic wavelength), one after another, instead of a built-in green filter. The images were registered to compensate for the differences caused by eye movements during the image acquisition. Retinal SO₂ was measured using two wavelength oximetry. To evaluate sensitivity of the proposed method, SO₂ in the arterioles and venules before and after inhalation of 100% O₂ were compared, respectively, in 11 healthy subjects. After inhalation of 100% O₂, SO₂ increased from 96.0±6.0% to 98.8±7.1 in the arterioles (p=0.002) and from 54.0±8.0% to 66.7±7.2 in the venules (p=0.005) (paired t-test, n=11). Reproducibility of the method was 2.6% and 5.2% in the arterioles and venules, respectively (average standard deviation of five measurements, n=11).