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Justin V Migacz, Iwona M Gorczynska, Ravi Sankar Jonnal, Robert J Zawadzki, John S Werner; OCT Angiography of the Human Choriocapillaris at 1.7M A-scans/second. Invest. Ophthalmol. Vis. Sci. 2016;57(12):444. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Optical coherence tomography angiography (OCTA) is an emerging tool for imaging vasculature in the healthy and diseased retina. Because image acquisition usually takes several seconds, involuntary saccadic movements of the eye create skew distortions and discontinuities in the resulting images, leading to an inaccurate representation of the vessel network. This is a significant problem when imaging the smallest vessels of the choriocapillaris. We have designed and constructed a small field of view (5x5 degrees), raster-scanning swept-source OCT system capable of imaging the human retina and choroid at 1.7 million axial scans per second, which is the fastest speed of any ophthalmic OCT system and about 20 times faster than commercial systems. With this extraordinarily high imaging speed, we are able to capture high-quality vessel maps of the choriocapillaris with a dramatic reduction of motion artifacts and distortions.
Our custom OCT system used a commercial swept-source laser (OptoRes GmbH, Munich, Germany, λ=1060 nm, Δλ=80 nm) with a sweep repetition rate of ~1.7MHz. The optical power of the OCT light beam on the cornea was 1.8mW. Single volumes spanned ~0.7x1.5mm on the retina and images of multiple locations were acquired, and tiled in post-processing. Angiograms were rendered from the volumetric data using multiple processing algorithms, including the phase-variance and amplitude decorrelation methods.
In cross-sectional intensity images, motion of blood was visible in the retinal vascular plexi and choroidal layers, with the high frame rate permitting observation of the passage of small (5–10µm) objects in the vessels. High-contrast angiograms of the retina were generated, such as the ones shown in Figures 1 and 2. These images show clearly the microscopic structure of the choriocapillaris, and were acquired in a fraction of the time of most other OCTA systems.
Our 1.7M A-scan/sec acquisition speed OCTA system is capable of producing choriocapillaris images with high contrast, higher than when averaging multiple slower volumes. These images can facilitate our understanding of the role played by microscopic vascular structures in diseases of the outer retina.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Choriocapillaris at 8° nasal, 2.5° superior from the fovea
Choriocapillaris at fovea
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