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Denise Valente, Brian Vohnsen; Retinal Simulator for Refractive Eye Models and Retinal Implants. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4210.
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© ARVO (1962-2015); The Authors (2016-present)
Neither refractive eye models nor retinal implants do currently take into account the directional properties of the photoreceptors. The purpose of this study is to manufacture and experimentally validate a waveguide-based retinal simulator that can be attached onto eye models and retinal prostheses with optical properties that resemble those of the photoreceptors.
The waveguide-based simulator was manufactured by UV lithography using a chrome mask with a 50 µm AZ40 XT photoresist film producing arrays of parallel cylindrical waveguides. Each waveguide core in the latent image has a slightly increased refractive index as verified by optical interferometry. The effective directionality of the waveguides, and thus their acceptance angle, was determined by angular scanning with respect to an incident collimated beam of light (543 nm wavelength) with the simulator imaged onto a CCD camera. Recorded images were analyzed with ImageJ and Matlab to determine the total power coupling efficiency for each waveguide.
It is found that the transmitted power through the waveguides decreases for oblique light thereby mimicking the angular sensitivity of the photoreceptor cones and the Stiles-Crawford effect of the first kind. However, the measured directionality is smaller than the theoretically expected by an array of waveguides with the same numerical aperture. Leakage of light was also observed which suggests that the finite length of the waveguides may still not suffice to effectively decouple radiative modes.
Arrays of cylindrical waveguides were realized in photoresist that resemble the angular sensitivity to light of retinal photoreceptor cones. With further development this may prove an essential add-on for refractive eye models and next-generation retinal implants to reduce the impact of intraocular scattered light by angular filtering.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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