Reflected light imaging of ON and OFF responses in frog retina

Using a near infrared (NIR) light flood-illumination imager equipped with a high-speed CCD camera, we demonstrated reflected light imaging of stimulus-evoked retinal ON and OFF responses in isolated, but intact, frog eye. Both fast and slow transient intrinsic optical signals (IOSs) were observed. Fast optical response occurred immediately after the stimulus onset, and correlated tightly with the ON and OFF edges of the visible light stimulus. High resolution images revealed both positive (increasing) and negative (decreasing) IOSs, and dynamic optical change at individual CCD pixels could often exceed 10% of the background light intensity. Our experiment on isolated eye suggests that further development of fast, high resolution fundus imager will allow robust detection of fast IOSs in vivo, and thus allow noninvasive, three-dimensional evaluation of retinal neural function.