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Toshiaki Nakagawa, Atsushi Kakuuchi, Takayoshi Suzuki, Shinji Toyoda; Retinal oximetry using stereo retinal fundus camera with band-pass filter. Invest. Ophthalmol. Vis. Sci. 2013;54(15):45.
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© ARVO (1962-2015); The Authors (2016-present)
To measure hemoglobin oxygen saturation (SO2) in the retinal blood vessels by use of a stereo fundus camera with two narrow band-pass filters.
Stereo retinal fundus image pairs were taken simultaneously using a prototype stereo fundus camera with two narrow band-pass filters, which was modified from a commercially available stereo fundus camera (nonmydWX, Kowa Company, Ltd., Japan). The two different filters were inserted into the left and right of light paths, respectively. The center wavelengths of the filters were 570 nm and 600 nm and the half-bandwidth was 10 nm. Namely, the stereo retinal fundus image pair consists of a left image and a right image of the same area with 570-nm and 600-nm light. This was able to be generated by taking a single shot using a single sensor, the images were acquired with a digital camera (D90, Nikon Corporation, Japan) attached to the stereo fundus camera. Images were 4288 × 2848 pixels in size with a 27° field of view. SO2 of the individual blood vessel was measured using specially developed software were obtained with the two-wavelength algorithm proposed by Beach et al. (J Appl Physiol., 1999). The blood vessels were extracted by using the black-top-hat transformation, which is a type of grayscale morphological operation, from the 570-nm image of the stereo retinal fundus image pairs. Optical density ratio (ODR) for each blood vessel was calculated and SO2 was calculated as SO2 = 1.96 − 6.00 × ODR. Six stereo fundus images were taken from both eyes of 3 healthy volunteers (age 41 ± 7.2 y) without mydriasis. Mean SO2 was measured in 71 artery and 67 vein segments.
SO2 was 97.2 ± 16.0 % (mean ± SD) in arterioles and 58.5 ± 13.9 % in venules. There was a significant variation of the SO2 of the individual arteriolar and venular vessels (p<0.0001).
Experimental results show that the proposed technique could be useful for the SO2 measurements in the retina.
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