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Yifan Jian, Kevin S.K. Wong, Michelle Cua, Stefano Bonora, Robert J Zawadzki, Marinko V Sarunic; Wavefront sensorless adaptive optics OCT with real time axial tracking for imaging human retina. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4096.
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© ARVO (1962-2015); The Authors (2016-present)
We describe our wavefront sensorless adaptive optics optical coherence tomography (WSAO-OCT) system for imaging the human photoreceptor mosaic in vivo. Real time segmentation of the retinal OCT B-scan permitted axial tracking and extraction of en face images. We validated our system performance by imaging the retina at several eccentricities, and demonstrated the improvement in photoreceptor visibility with WSAO aberration correction.
A human WSAO-OCT system was constructed using lenses (instead of mirrors), delivering a 5.5mm (diameter) at the subject’s pupil. The OCT engine acquired A-scans at a rate of 200 kHz, and volumes of 1024x200x80 voxels were acquired in ~0.1 s. A custom written GPU program tracked the layer of interest initially selected by the operator using a simple retinal segmentation algorithm, and then extracted the corresponding en face projection image. The modal WSAO algorithm optimized Zernike radial orders 2 to 4 in order to maintain a balance between optimization time and effective aberration correction. For each Zernike mode, the optimization was performed by acquiring an OCT volume and extracting an en face image for each of 5 different coefficient values. The coefficient that produced the brightest en face image was selected as the optimized value. The entire optimization process required 6~12 seconds, depending on the amount of the aberrations in the subject’s eye.
We present en face images acquired at three different retinal eccentricities before and after WSAO optimization in Figure 1. In the unoptimized images, the cones are mostly indistinguishable from speckle pattern. After optimization, the image contrast increased, and the cone mosaic can be resolved.
We demonstrated a lens-based approach for WSAO-OCT that is capable of resolving the cone mosaic in the human eye at small angles of eccentricity with non-mydriatic pupils even with a small-stroke DM. The reduced complexity of the lens-based WSAO design can facilitate a robust and compact imaging system that is highly suitable for clinical applications in ophthalmology.
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