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Koichi Ito, Naoto Honda, Hiroyoshi Nakanishi, Masaaki Hanebuchi, Naoki Isogai; Optical Design of Ultra-Wide-angle Fundus Imaging Device Using Four-color Lasers. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5872.
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Many conventional fundus imaging devices have a viewing angle of approximately 45° and cannot perform wide-angle imaging without taking multiple images. In this experimental study, we tested an optical design using a confocal scanning system for acquiring ultra-wide-angle fundus images using a four-color laser.
To achieve a compact optical arrangement a refractive optical system with an objective lens was designed. An adapter lens unit was created for ultra-wide-angle imaging. An objective lens that converges light rays is advantageous for achieving a compact optical system. However, light reflected from the objective lens surface creates a bright spot (optical noise) due to a weak SLO signal from the fundus. The optical arrangement was designed to compensate for the optical noise to mini the bright spot artifact.
In the confocal optical system, optical noise around the image plane can be reduced with a small confocal aperture. However, obtaining a ultra-wide-angle image requires a specific focus depth which is impossible with an extremely small aperture. We used a hole mirror to separate the light projecting system and light receiving system, and placed a black spot plate in the receiving system to mitigate the bright spot artifact. Additionally, multiple objective lenses were used as a lens group, some of which we decentered to prevent direct reflection of noise returning to the receiving system. As a result, bright spot noise was significantly reduced without lowering the efficiency of the SLO signal. Images of human eyes were acquired using this prototype optical system, with high quality images, suitable for ophthalmic diagnosis. An angle of view of 60° was achieved with an ordinary objective lens optical system, and 110° with an ultra-wide-angle adapter.
Our prototype optical design was more compact than conventional fundus imaging devices and achieved larger viewing angles suitable for ultra wide field imaging.. Incorporation of decentered objective lens, hole mirror, and black spot plate allowed high-quality fundus imaging with significant reduction of optical noise and artifacts.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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