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Eva Acosta, Justo A Arines, Miguel Olvera-Ángeles, Alfonso Padilla-Vivanco, Jose Sasian, Jim Schwiegerling; Extending depth of focus of ophthalmic elements with trefoil aberration. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5803.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of this work is to design, fabricate and test a contoured plate that introduces a phase shift that varies cubically across the pupil providing simultaneous near and distance focused vision. We seek invariance of the response of the system rather than multifocality.
Computational Fourier Optics is used to obtain the magnitude of a trefoil aberration that provides the deepest range of clear vision. The neural transfer function is taken into account to evaluate the Modulated Transfer Functions (MTF) which provide the depth of focus. The size of photoreceptors is taken into account for the simulations of retinal images. The shape of a PMMA phase plate is designed with Zemax.
Numerical simulations show that trefoil aberration degrades the PSF, but it does it uniformly through-focus. Moreover, the MTF’s are not only invariant but also have no zeroes (no loss of details). Loss of contrast is predicted. Retinal images were also simulated for different pupil sizes, and we did not find qualitative differences.The required amount of trefoil aberration for maximum depth of focus with an acceptable contrast is 135λ @550nm. The shape of the plate in polar coordinates isS(ρ,θ )=α(ρ3cos3θ)+A(6ρ4-6ρ2) with α=152μm and A=1.7 μm.The plate introduces some chromatic defocus, which slightly reduces the predicted depth of focus @550nm.We tested the plate in a highly myopic subject (-6.00D). Acuity was measured at 4.0m with an ETDRS chart. With no correction, the subject was only able to identify one letter on the top row, corresponding to a LogMAR acuity > 1.0. The phase plate was held near the subject’s right eye, increasing monocular acuity to 0.8. For the left eye monocular acuity increased to 0.7. Finally, a pair of plates were used to assess binocular performance, leading to an acuity of 0.6. The process was repeated with a Rosenbaum pocket vision screener at 35cm. Without correction, the subject’s near acuity was >J16. For the right and left eyes with the phase plate, the monocular acuities were J5 and J7, respectively. Finally, the binocular acuity was between J3 and J5.
Contact or intraocular lenses the design of which includes large amounts of trefoil aberration can be an alternative design to multifocal contact or intraocular lenses for presbyopia correction. This is due to the fact that the resulting PSF is relatively uniform both across the image plane and through an extended focal range.
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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