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Akos Kusnyerik, Balazs Rozsa, Janos Nemeth, Pal Maak; Sequential Model for Retinal 2-Photon Imaging in the Human Eye. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3101.
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We intend to use two-photon microscopy for assessing functional activity on sub-cellular level in the human retina. Our aim was to exhaust possibilities of a novel acousto-optic 3D scanning method to adapt our system for different samples and configurations during in vivo imaging.
Optical engineering was performed in ZEMAX software (ZEMAX-EE Optical Design Platform). The model of a 3D acousto-optic scanner was combined with a sequential eye model. We developed a lens with aspheric surfaces to match the microscope to the eye samples that generally compensated the major optical aberrations. The adaptive potential of the acousto-optic scanner was tested using measured data from different eyes and analyses reported in the literature. (J. Schwiegerling: Visual and Ophthalmic Optics, SPIE Field Guides FG04, 2004.) The varied parameters were the anterior chamber depth (3.5-4.3 mm), crystalline lens length (3-3.6 mm), as well as front and back radius of curvature (13.2-14 mm and -5.6 to - 6.5 mm, respectively). These data were fitted into a sequential eye model based on the model elaborated by Liou & Brennan (LBE). The aspheric matching lens was generated using a certain set of average parameters.
The use of the coupling aspheric lens efficiently reduced the minimum lateral PSF (point-spread function) size to 2.5 µm which is very near to the diffraction limit, in the case of average eye parameters. Furthermore we used effectively the potential of the electronic compensation offered by the acousto-optic lenses maintain the lateral resolution in the 2.5-4 µm range over a field of view of 150 µm radius in all individually parameterized eyes. We found that the natural spread in focusing power of the analyzed eyes (48-62 D) can be fully compensated with the acousto-optic focusing feature, which nominally allows a z scanning range of more than 1600 µm in tissue. Strength of acousto-optics is in the compensation for astigmatism, since it provides separate focusing possibility in two distinct perpendicular planes.
Modeling shows that acousto-optic two-photon microscopy is a flexible tool for acquiring structural and functional information from eyes with large spread in power and optical imaging errors. Our next goal is to implement and confirm the results in a clinical study.
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