A New Two-Spectral-Band Functional Imaging Fundus Camera Reveals Oxygen Saturation Level of the Retinal Artery and Vein

Abstract

Purpose: : Recently, intrinsic optical imaging of the retina has been studied by several groups. The methods used by the most groups were monochromatic sequential imaging using fundus cameras revealing the response in the intensity of reflections from arteries and the other parts of the retina. In this study, we built a two-spectral-band functional imaging fundus camera (FIF2S) and one of the purposes of the instrument was monitoring oxygen saturation (OSat) level as a response to stimulation. Validity of optical density (OD) of the vessel and that of saturation level were investigated using the new instrument.

Methods: : The retina of the eye of a cat under general anesthesia was observed using a two-spectral-band (730-780nm, 820-880nm) functional imaging fundus camera based on a mydriasis type fundus camera (TRC-50LX, Topcon). A white light stimulation and transcorneal electrical stimulation (TES) were applied. The retina was observed 40 frames per second by two high quality CCDs. We recorded the retina for 2 s before stimulation, then for 4 s during stimulation, and finally for 20 s after stimulation. We measured intensities on and by the artery and the vein, and analyzed OD and OSat.

Results: : ODs of the veins did not vary for the two kinds of stimulations in both spectral bands. ODs of the arteries increased during the light stimulation and peaked at the cessation of the stimulus and then gradually decreased in 820-880nm band. ODs of the arteries with TES in both spectral bands varied in the same way as that with the light stimulation and the variation in 820-880nm band was larger than that in 730-780nm band. All OSats measured on the arteries were larger than those on the veins. OSat of the artery with TES decreased during the stimulation and increased after the stimulation.

Conclusions: : OSat of the artery in the retina decreased in response to TES. This suggests that TES initiated the consumption of oxygen in the artery as the metabolic changes in the retina. The variation of the OSat by the light stimulation was smaller than that by the electric stimulation. Thus variation of OD of the vessels by optical or electrical stimulations can be evaluated using the new FIF2S.

Keywords: imaging/image analysis: non-clinical • metabolism • neuro-ophthalmology: diagnosis