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Barry Cense, Kenta Sudo, Kazuhiro Kurokawa, Yoshiaki Yasuno; Adaptive Optics-Assisted Optical Coherence Tomography For Patient Imaging. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5603.
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As optical coherence tomography (OCT) systems become faster, the short acquisition time per depth scan leads to a reduced image quality. Since sending more light into the eye is limited by standards for safe use of light, we optimized the light collection efficiency by using a larger beam size and adaptive optics. The purpose of this study is to image the retina of healthy subjects and patients with retinal pathology with a small and low cost adaptive optics-assisted optical coherence tomography (AOa-OCT) system and to compare the image quality to images obtained with a commercial OCT system.
We built an AOa-OCT system around a Boston Micromachines 140 actuator 5.7 micrometer stroke deformable mirror and an ImagineEyes HASO Shack Hartmann sensor. By using a dual axis galvanometer with a single mirror surface, we minimized the number of telescopes to one, thereby keeping system astigmatism to a minimum. We optimized the optical design of the system with ray-tracing software, to find a sweet spot for OCT imaging: a 3.4 mm beam (1/e2 diameter) entering the eye allows for diffraction-limited performance over an isoplanatic patch of 10 degrees and a Rayleigh length that encompasses the full retinal thickness. This system was built on a 25 cm x 50 cm optical breadboard. AO operation was performed at 12 Hz, and diffraction-limited performance was reached routinely for subjects without dilation and prescriptions up to +/- 3D of sphere. Acquisition time per B-scan (1000 A-scans) was 40 ms. In the commercial system, patient eyes were corrected for defocus using the built-in Badal optometer.
AOa-OCT images were taken on healthy subjects and patients with pathology, and compared to images taken with a commercial system. The lateral resolution and speckle size improved by a factor of 3, and the dynamic range in the images (defined as the highest pixel value above the noise floor) was approximately 4 times or 6dB higher.
In comparison to standard OCT for retinal imaging, AOa-OCT offers an approximately three times higher lateral resolution and smaller speckle size over a 10 degree field of view. Since more photons are collected in comparison to standard OCT, the image quality is significantly better, with gains in dynamic range up to approximately 6 dB.
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