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Clara Pfäffle, Dierck Hillmann, Hendrik Spahr, Lisa Kutzner, Sazan Burhan, Felix HIlge, Yoko Miura, Gereon Huttmann; Functional imaging of retinal neurons using OCT. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6083.
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© ARVO (1962-2015); The Authors (2016-present)
Recently, non invasive functional imaging of the retinal photoreceptor cells has been shown, using phase stable optical coherence tomography (OCT). In our work, we want to characterize those intrinsic optical signals (IOS) to link them to the biochemical processes causing those optical changes. This knowledge helped us to visualize IOS in the ganglion cell layer.
The IOS were imaged by FF-SS-OCT, which is able to detect sub-wavelength morphological changes by phase evaluation. The required phase stability is reached by parallel illuminating the field-of-view and detecting with an area camera (FASTCAM SA-Z, Photron) at frame rates of up to 75 kHz. The OCT uses wavelengths between 867 and 816 nm, which are outside the sensitivity range of the human retina. White light was used to stimulate the retina. Both, OCT and stimulation light, were below the maximal permissible exposure, as confirmed by the responsible safety officer. The study was approved by the ethic boards of the University of Lübeck.
The observed IOS in the photoreceptor cells are caused by a change of the optical path length of the outer segments. Due to the magnitude and time course of the IOS and its dependency on stimulus intensity we assumed osmotic driven volume change which lead to the observed elongation. Osmotic changes are also expected for other cell layers of the retina when ion concentrations change by neuronal activity. Therefore, such changes of the optical pathlength should be visible for example in the ganglion cell layers, although the magnitude is expected to be considerably smaller. With this knowledge we were able to visualize expansion of the OPL between ganglion cells and inner plexiform layer after stimulation. The parallel imaging of activated photoreceptor and ganglion cells enables us to generate a wiring map, which shows a lateral translation of connected neurons radially away from the fovea. The translation is biggest in the direct neighborhood of the fovea and becomes smaller in the periphery. These results are confirmed by previous anatomical studies, which show similar results for the wiring behavior of photoreceptor and ganglion cells.
The functional imaging of the ganglion cell layer suggests that in general all retinal neurons exhibit measurable optical changes. Visualizing the function of the different neurons in the retina, in vivo, yields a possibility for investigating the visual post processing of the retina.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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