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Diego Rativa Millan, Ralf Blendowske, Brian Vohnsen; Effects Of Waveguide Properties Of Human Photoreceptor Cones, Simulating Its Optical Properties With A Photonic Crystal Fiber. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3206.
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The cone cells are known to work as waveguides that guide light from the inner to the outer segments where the visual pigments are contained. Different models have been introduced to describe the light-guide mechanism, its relation to the Stiles-Crawford effect, and its effects on aberrations and visual sensation. However, the models are considered abstractions and their formulations may miss essential details of the real eye. Here, our goal is to gain insight into the waveguide characteristics and its aforementioned effects by comparison with a fiber-based photoreceptor simulator.
We have used an optical setup with a lens to imitate the optics of the human eye and a liquid-filled photonic crystal fiber (LF-PCF) to imitate the photoreceptor cone mosaic (D. Rativa, B.Vohnsen, Biomed. Opt. Express, submitted). Simulated Stiles-Crawford measurements for the artificial eye and retina based on transmitted power measurements have been performed under single- and multimode waveguide conditions (as managed by temperature) across the visible spectrum. Furthermore, low-order optical aberrations have been introduced using a deformable mirror located at the conjugate pupil plane, and differences of guided and non-guided point-spread-function images are studied corresponding to effective retina images of the human eye.
As evidenced by the fiber-based retina simulator we have observed changes of the pupil apodization caused by single- and multimode transitions of the waveguides. These variations are compared with the apodization shapes acquired by independent psychophysical Stiles-Crawford measurements of the author’s eyes. The transmitted light power by the LF-PCF decreases with the increase of the pupil aberrations allowing a direct study of the influence that corresponding aberrations may have on effective retinal images and the accommodation mechanism of the human eye.
The detailed apodization shape and the high sensitivity to the refractive indices of the retina simulator have proven ideal to test the concept of waveguiding for a structure that resembles the organization of cone photoreceptors in the human eye. Waveguide coupling reduce the impact of aberrations in the retinal simulator and suggest that a similar mechanism exists in the human eye playing a role for vision and the accommodation mechanism.
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