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Theodore DuBose, Francesco LaRocca, Sina Farsiu, Joseph A Izatt; Optical photon reassignment super-resolution scanning laser ophthalmoscopy. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3809. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Scanning laser ophthalmoscopy (SLO) is a type of confocal imaging and therefore optimal resolution is only achieved in the limit of an infinitely small pinhole and at the expense of signal-to-noise ratio (SNR). Optical photon reassignment (OPRA) microscopy, is an all-optical (free from image reconstruction) super-resolution microscopy technique that achieves optimal confocal resolution without an SNR tradeoff. However, to date, OPRA has only been demonstrated for microscope imaging of fluorescent samples. Therefore, we present a system and preliminary results for obtaining super resolution in retinal imaging with the first SLO system employing OPRA.
Light was scanned onto the eye by a double-sided 8 kHz resonant scanner and a galvanometer scanner. The returning light was magnified, rescanned by a second galvanometer scanner and the backside of the resonant scanner, and imaged onto a camera. The system was configured to achieve either widefield imaging resolution or OPRA resolution by changing the intermediate transverse magnification between the descanned light from the sample and the rescanned light.
To experimentally verify the resolution improvement for the system, we imaged a 1951 USAF test target, in both the widefield-equivalent and OPRA configurations, as shown in Fig. 1. The resolution improvement factor in terms of full width at half maximum (FWHM) was 1.40 and 1.32 for the horizontal and vertical directions, respectively, which compares favorably to the theoretical expected improvement of 1.41. Retinal image mosaics acquired with and without OPRA are shown in Fig. 2. The cone photoreceptors are much clearer (Fig. 2 C-F) in the OPRA-enhanced images than in the widefield images.
We have demonstrated optically super-resolved retinal imaging by combining SLO with OPRA to achieve improved visualization of parafoveal cone photoreceptors without the typical confocal loss of SNR. The use of this technology may provide increased resolution capabilities for either conventional SLO systems or those employing adaptive optics.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
(A) Widefield vs (B) OPRA SLO imaging of a test target. Red and blue boxes indicate the locations where the horizontal and vertical line spread functions were calculated. (C-F) Corresponding line spread functions with indicated FWHMs.
(A) Widefield equivalent vs (B) OPRA retinal image mosaics at a 2.3° eccentricity. (C-F) Detailed views with a 0.3° x 0.3° FOV.
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