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Toshifumi Mihashi, Yoko Hirohara, Yoshiyuki Kitaguchi, Takeshi Morimoto, Tomomitsu Miyoshi, Takashi Fujikado; Differences in the independent components in two-spectral-band for retinal functional imaging . Journal of Vision 2009;9(14):88. doi: 10.1167/9.14.88.
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We have developed a functional imaging fundus camera with two-spectral-band observation (730–780 nm, 820–880 nm) to reveal oxygen saturation in the retina. The eye of the cat was studied under general anesthesia. The retina was stimulated by a visible light stimulus or trans-corneal electrical stimulus two seconds after the onset of experiment and the duration was four seconds. One sequence of measured images in one spectral range consisted of 1000 images for a 26-second imaging duration at 40 frames per second. We repeated the sequence 10 times and averaged the ten images at the same timing in the sequences. After obtaining two-spectral-band images, we performed independent component analysis and obtained ten components. Each component consisted of an image for 730–780-nm band and an image for 820–880-nm band. We obtained a time course of each component performing back-projection of the independent component to the 1000 raw images. We investigated differences between a 730–780-nm band image and 820–880-nm band image in the components.
We found three kinds of differences between the two spectral bands at independent components. Firstly, we obtained components that included reflectance changes on the vein in the 820–880-nm image but not in the 730–780-nm image. The reflectance rose slightly just after the stimulus onset and it decreased towards opposite polarity 4 seconds after the onset. In 820–880-nm spectral band, optical absorption of oxi-hemoglobin is larger than that of deoxi-hemoglobin. Because we observed the reflectance of the back of the retina that penetrated through the blood vessel, the more reflectance we observe, the less oxi-hemoglobin the blood vessel has. We could interpret the time course of reflectance as the vein had less oxi-hemoglobin just after the stimulus onset with metabolism caused by the stimulation and then the vein had more oxi-hemoglobin several seconds after the onset with the additional blood supplied by the artery.
Secondly, we found a component that included a response of choroidal vessels only in 820–880-nm images. We speculated that the cause is that the retinal tissue in 820–880-nm is more transparent than that in 730–780 nm. The other difference is in components that include the reflectance change in the area around the disk. Although we found this in a 730–780-nm component and in an 820–880-nm component, the area in the 730–780-nm component was larger than that in the 820–880-nm component. Finally, the tendency of the patterns was the same for both optical and electrical stimulations.
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