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Tilman Schmoll, Daniel Bublitz, Nathan D Shemonski, Lars Omlor, Christoph Nieten, Matthew J Everett; Partial Field Holoscopy. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3810. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To improve the resolution and collection efficiency of optical coherence tomography (OCT) systems. Today’s ophthalmic OCT systems detect only about 5% of the light exiting the pupil because they use only about 20% of the eye’s numerical aperture (NA). To overcome this, we introduce partial field holoscopy, which creates images of the human retina with high detection efficiency and high spatially in-variant resolution.
We built an in-vivo swept source partial field holoscopy system, which illuminates the retina with a low NA beam and collects the backscattered light with a high NA using a spatially resolved detection unit. It consists of 2 detectors, arranged in a balanced detection configuration, each containing 37 detection channels. In conjunction with the 10 kHz, 1060 nm swept source this results in an effective A-scan rate of 370 kHz. For computationally correcting defocus and aberrations of the eye, we require phase sensitive, angle diverse data. Access to the phase is enabled by the interferometric nature of the imaging method and angle diverse information is provided by the spatially resolved detection unit. For reconstructing volumes with spatially invariant resolution, we use the subaperture correlation based digital adaptive optics algorithm (A. Kumar et al. Opt. Express 2013).
Images of reflective as well as highly scattering test targets were acquired. A significant resolution improvement was observed after defocus correction, even in heavily scattering samples (Fig. 1). In Fig. 2 a first in-vivo retina scan can be seen. Fig. 2e demonstrates speckle reduction by incoherently adding the 37 detection channels.
Partial field holoscopy enables a detection efficiency and resolution otherwise only achievable with hardware adaptive optics. The angle diverse and phase sensitive nature of the captured data will enable many exiting extensions, e.g. photoreceptor imaging, quantitative blood flow measurements, tissue specific directional scattering contrast, dark field imaging.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Fig. 1 a) group 6 elements 2&3 of USAF resolution test target, showing the resolution improvement after digital correction; b) USAF target with scotch tape on top, to demonstrate computational refocusing of highly scattering samples
Fig. 2 a) In-vivo prototype; b) fiber array used as detector; c) average b-scan of 37 detection channels; d) center channel b-scan of section indicated by red box; e) average of all 37 channels, showing significant speckle reduction
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