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Ramkumar Sabesan, Vimal Prabhu Pandiyan, Aiden Maloney-Bertelli, James A Kuchenbecker, Austin Roorda; Adaptive optics line-field OCT for high-speed imaging of retinal structure and function. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1780.
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© ARVO (1962-2015); The Authors (2016-present)
Line-field OCT offers an avenue to visualize depth-resolved retinal structure and function with high sensitivity, speed and phase stability. Here, we incorporate adaptive optics(AO) into this platform to demonstrate cellular-scale imaging of cone photoreceptor structure and function
An AO line-scan imager was constructed in free-space to include 3 illumination and 3 detection channels. An 840±25nm source was used as illumination for OCT and line-scan ophthalmoscope(LSO), a 980±10nm source for wavefront sensing, and a 660±10nm LED in Maxwellian view for retinal stimulation. In detection, a 1200 line-pairs/mm diffraction grating and a high-speed 2D camera formed the spectrometer for OCT, a line-scan camera placed at the zeroth diffraction order of the grating formed the detection channel for LSO and a wavefront sensor measured aberrations. A maximum imaging field of 2x2deg was allowable by illuminating a line-field on the retina using a cylindrical lens and scanning it using a 1D galvo-scanner. OCT volumes and LSO images were acquired at 1.5-5 deg temporal ecc. through a 6.7mm dilated pupil. To probe light-activated cone function, 2-sec OCT volumes were acquired after 3 min. dark adaptation, followed by a 30ms flash stimulus. The temporal evolution of phase difference was computed between individual cone inner/outer segment junction and outer segment tips to yield a measure of light-induced optical change in cones.
In both LSO and OCT, AO improved image quality substantially and lateral resolution was ultimately limited by the Nyquist spatial sampling in detection. OCT sensitivity was linear with B-scan acquisition speed - 91dB for the minimum(2.5kHz) B-scan rate. The phase sensitivity was 4mrad at 50dB SNR. Cone mosaics in OCT were clearly resolved at speeds between 3kHz-16kHz B-scan rate, corresponding to 10 – 50 volumes/sec for 300 line-scans per volume. Individual cones exhibited a light-induced optical response characterized by an increase in path length of their outer segments and modeled by an exponential function saturating at 105-140 nm on average, 300-500ms after stimulus flash.
High-speed volume acquisitions, high phase stability and cellular resolution demonstrate the potential of AO line-field OCT for imaging retinal structure and function.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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