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James E. Morgan, Irina A. Erchova, James Fergusson, Alexandre R. Tumlinson, Frank Sengpiel, Wolfgang Drexler; Optophysiological Characterisation of Retinal Ganglion Cell Responses to Bleach Stimuli by UltraHigh Resolution Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2195.
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Functional characterization of retinal neurons in response to light flashes is essential for clinical testing and diagnostics. The purpose of this project was to test whether light driven activity in the inner retina could be detected and quantified in vivo by UltraHigh Resolution Optical Coherence Tomography (UHR-OCT).
We developed an efficient 1050 nm Fourier domain UHR-OCT device for retinal imaging. The device was linked to animal electrophysiological recording from the lateral geniculate nucleus (LGN) in treeshews and superior colliculus (SC) in rats. Animals (treeshew n=2 and rat n=2) were anaesthetized with 1.2% isoflurane and the ocular movements were minimized by application of neuromuscular blocking agent gallamine to allow imaging of the same retinal areas over time. The EEG, heart and respiratory rate were monitored during these experiments and used to gate the acquisition and image processing. A small area of retina 60 um2 was sampled optically every 20 ms for 5s. Light flashes of different intensity (max 95% cone bleach) were presented for 2s; a recovery period up to 30 min was allowed between different stimuli.
Stimulation with bright flash (bleach) resulted in changes in inner retinal optical responses that coincided temporally with the flash and the magnitude of evoked responses correlated with flash brightness. For the brightest flash the average change in contrast was 27% for ON response and 22% for OFF response, with individual values ranging from 2.2% to 62%. A variety of temporal patterns of response were observed on the time scales from 60 ms to 1200 ms (on average 415 ms). Some of the patterns were consistent with average firing rate responses of retinal ganglion cells (short latency phasic responses with ON or OFF preferences); the other patterns (longer latency tonic responses) were more likely to originate from blood vessels/glia.
We have successfully developed a 1050nm Fourier domain UHR-OCT customized for animal use which can generate optical cross sections of the retina in vivo. Using this set up we were able to demonstrated light-evoked optical changes in the inner retina consistent with both metabolic and functional RGC responses.
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