Abstract
Purpose :
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
Methods :
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.
Results :
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.
Conclusions :
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.