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Eva Acosta, Justo Arines, Rene Hernandez, Adrian Grewe, Stefan Sinzinger; Wavefront coding implementationfor retinal imaging systems. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1586.
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© ARVO (1962-2015); The Authors (2016-present)
To experimentally demonstrate the feasibility of using wavefront coding technique (WCT) for high resolution retinal imaging avoiding wavefront sensing or wavefront correction of the spatial and dynamic variations of the eye aberrations.
A cubic phase plate iplate fabricated in PMMA by ultraprecision micromilling is placed in the exit pupil of an optical system that provides magnified images of an artificial fundus. The plate has a trefoil shape, with 38 waves peak to valley aberration within 5mm pupil. The artificial retina consist in a USAF-1951 resolving power test negative target located at the fundus of a model eye where both low and high order eye aberrations have been included by means of a phase plate fabricated in photoresist. The cubic phase element is intended to blur images in such a way that invariance to optical aberrations is achieved. The blur is then removed by image post-processing by restoring images by means of a Wiener filter which uses the PSF of the optical system with the cubic phase plate.
We fabricated and characterized a phase plate in trefoil shape in order to implement WCT in eye fundus imaging. The plate generates not only trefoil but also some small amounts of other aberrations. We set up an optical system that allows recording distorted images of an artificial retina illuminated with a 625nm LED. Once decoded, the blurry images corresponding to eye aberrations and cubic phase plates are considerably sharper than those recorded without the cubic phase plate. We obtained that the used hybrid optical-digital processing device has a resolution of about 10 microns. Nevertheless, both the phase plate design and the image processing can be improved and we expect to increase the resolution obtained in this proof of concept.
WFT can be used to obtain high resolution retina images. The experimental results show that the technique can provide retinal details under 10 microns resolution for a wide range of eye aberrations and therefore significantly reduce the complexity, size and cost of some of the current systems by no longer having to sense and correct high order ocular aberrations and also allowing some degree of flexibility for remaining amounts of defocus and astigmatism. The optical system could be also integrated in a compact and inexpensive device because it does not need wavefront sensors and deformable mirrors.
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