Stiles–Crawford effect (SCE) is exclusively observed in cone photoreceptors, but why the SCE is absent in rod photoreceptors is still a mystery. In this study, we employed dynamic near infrared light imaging to monitor photoreceptor kinetics in freshly isolated frog and mouse retinas stimulated by oblique visible light flashes. It was observed that retinal rods could rapidly (onset: ∼10 ms for frog and 5 ms for mouse; time-to-peak: ∼200 ms for frog and 30 ms for mouse) shift toward the direction of the visible light, which might quickly compensate for the loss of luminous efficiency due to oblique illumination. In contrast, such directional movement was negligible in retinal cones. Moreover, transient rod phototropism could contribute to characteristic intrinsic optical signal (IOS). We anticipate that further study of the transient rod phototropism may not only provide insight into better understanding of the nature of vision but also promise an IOS biomarker for functional mapping of rod physiology at high resolution.
This study is to test anatomic correlates, including connecting cilium (CC) and inner segment (IS) ellipsoid, to the hyper-reflective band visualized by optical coherence tomography (OCT) and commonly attributed to the photoreceptor inner/outer segment (IS/OS) junction. A line-scan OCT (LS-OCT) was constructed to achieve sub-cellular resolution (lateral: ∼ 2 μm; axial: ∼ 4 μm) of excised living frog retinas. An electro-optic phase modulator was employed for rapid and vibration-free phase modulation. Comparison of normalized distance measurements between LS-OCT images and histological images revealed that the dominant source of the signal reported as the IS/OS OCT band actually originates from the IS.
KEYWORDS: Information operations, Retina, In vivo imaging, Confocal microscopy, Near infrared, Image resolution, Line scan image sensors, Intrinsic optical signal, Imaging systems, Eye
Intrinsic optical signal imaging (IOS) promises a noninvasive method for high resolution examination of retinal function.
Using freshly isolated animal retinas, we have conducted a series of experiments to test fast IOSs which have time
courses comparable to electrophysiological kinetics. In this article, we demonstrate the feasibility of in vivo imaging of
fast IOSs correlated with retinal activation in anesthetized frog (Rana Pipiens). A rapid (68,000 lines/s) line-scan
confocal ophthalmoscope was constructed to achieve high-speed (200 frames/s) near infared (NIR) recording of fast
IOSs. By rejecting out-of-focus background light, the line-scan confocal imager provided enough resolution to
differentiate individual photoreceptors in vivo. With visible light stimulation, NIR confocal images disclosed transient
IOSs with time courses comparable to retinal ERG kinetics. High-resolution IOS images revealed both positive
(increasing) and negative (decreasing) light responses, with sub-cellular complexity, in the activated retina.
KEYWORDS: Information operations, Retina, Neurons, Visible radiation, Near infrared, Retinal scanning, Imaging systems, Visualization, Signal processing, Intrinsic optical signal
Simultaneous imaging of different retinal neurons functioning together can benefit better understanding of visual signal
processing mechanisms. In this paper we demonstrate that intrinsic optical signal (IOS) imaging allows simultaneous
monitoring of stimulus-evoked responses propagating from the photoreceptors to inner retinal neurons. High resolution
imaging revealed robust IOSs at the photoreceptor, inner plexiform and ganglion cell layers. While IOSs of the
photoreceptor layer were mainly confined to the area directly stimulated by the visible light; IOSs of inner retinal layers
spread from the stimulus site into relatively large areas.
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