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Stephen A Burns, Thomas Gast, Xiaofeng Qi, Ann E Elsner; High Speed Line Scanning AOSLO using a CMOS detector and dual scanning. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5203.
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© ARVO (1962-2015); The Authors (2016-present)
Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO) systems can provide high contrast, high resolution images of the living human eye but are limited in imaging speed by the need for a high speed scanning system. While higher frame rates can be achieved by scanning fewer lines and both directions of the scan can be utilized, the major limit is the line rate. For clinical work total imaging time as well as measurements of some physiological processes (ie. blood flow) could benefit from higher rates. We used a line scanning system and an sCMOS array detector, to provide a high speed confocal AOSLO with programmable control of aperture size.
We constructed a dual-mirror line scan AOSLO. A cylindrical lens focused a beam to a line, which was relayed to the deformable mirrors and then to a galvanometer mirror and finally to the human eye. The galvanometer located at the final relay before the eye scanned the line illumination across the retina. Light returning from the eye is first descanned, then relayed through the system to the SH sensor and a second galvanometer, which scans the image across the high sensitivity sCMOS detector (Hammatsu). The rolling shutter mode allowed control of the time each pixel line integrated light from the retina. By synchronizing the second scanner to the camera we placed the retinal conjugate in a known location relative to the pixels being exposed. Controlling the exposure time varies the effective aperture size. Wavefront sensing was performed at 857 nm and imaging at 720 nm. A model eye and two human subjects were tested.
Retinal images were acquired at 95 Hz with a line rate of 61 kHz. Confocality was documented by shifting the plane of focus; light return depended on focus and confocality (exposures from 4 to 40 lines). The system could be smoothly varied from images similar to those obtained with flood illumination to confocal images. The image quality in human eyes was good with photoreceptors and red blood cells visible, although contrast was decreased somewhat relative to a fully confocal system.
An sCMOS based line scan AOSLO can provide confocal retinal imaging at higher speeds with little loss of sensitivity. The sCMOS line scan system is simple and reliable since scanning is performed only at the final conjugates and there are fewer optical relays required than a 2D scanning system.
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