Abstract
Purpose: :
To validate the feasibility of imaging stimulus-evoked retinal activity in frog eye using fast intrinsic optical signals (IOSs), which have time courses comparable to ERG responses of the retina.
Methods: :
A high (~µm) resolution NIR light imaging system was constructed to detect transient IOSs in isolated (but intact) frog eye. While a white light flash was used for retinal stimulation, a continuous near infrared (NIR) light was used for optical imaging of stimulus-evoked retinal activity through ocular optics of the frog eye. By differentiating the pre-stimulus and after-stimulus images recorded with a high-speed (120 Hz) CCD camera, dynamic IOS images were constructed to characterize spatial and temporal properties of stimulus-evoked retinal activities.
Results: :
High spatiotemporal resolution NIR light imaging demonstrated transient IOSs in intact frog eye that was correlated with the visible light stimulation. Both fast and slow transient IOSs were observed. Fast IOSs occurred immediately after the stimulus onset, reached peak magnitude within 100 ms, and were correlated tightly with the ON and OFF edges of the visible light stimulus. Slow IOSs lasted a relatively long time (many seconds). Dynamic optical change at individual CCD pixels could often exceed 10% of the background light intensity. High resolution images revealed both positive (increasing) and negative (decreasing) IOSs in adjacent retinal areas.
Conclusions: :
NIR light imaging of fast IOSs could be obtained from isolated frog eye through intact ocular optics. High spatial resolution was necessary to obtain large transient IOSs of opposite polarities, because recording at a low spatial resolution would pool responses of opposite polarities together and would consequently reduce recorded fast IOS magnitude or even fail to record any fast IOS. We anticipate that further development of high (sub-cellular) resolution fundus imager, with high (> 100 Hz) imaging speed, will allow robust recording of fast IOSs in vivo, and thus make noninvasive, three-dimensional evaluation of physiological health of photoreceptors and inner retinal neurons possible.
Keywords: retina • neuro-ophthalmology: diagnosis • photoreceptors