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Vyas Akondi, Enrique Gambra, Maria Vinas, Sara Aissati, Carlos Dorronsoro, Daniel Pascual, Susana Marcos; Simulating multifocal intraocular lenses with a spatial light modulator and a tunable lens: a computational evaluation. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1272. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Vision simulators based on spatial light modulator (SLM) or tunable lens allow presbyopic patients to experience multifocal vision prior to intraocular lens (IOL) implantation. The pros and cons of these modalities are examined using computer simulations.
The phase of multifocal IOLs -diffractive trifocal, refractive bifocal and extended depth of focus (EDOF) IOLs- was estimated using geometrical profiles and pseudophakic computer eye models. Phase wrapped to the interval [0 2π] is addressable on a phase-only 8-bit SLM (pixel resolution: 1920 x 1080; pixel pitch: 8 µm). Tunable lens (0.2-1 kHz) based simulators (SimVis) work on the principle of time multiplexing and time coefficients for a multifocal design are optimized using through-focus (TF) Visual Strehl (VS) ratio metric. The accuracy in representing the IOLs, light efficiency, effects of pupil size and corneal aberrations were studied. The quality was assessed as the RMS difference between TF VS with the actual lens profile and the simulated lens.
Light efficiency (~51%) in SLM is limited by pixel diffraction (87% fill-factor gives 73% diffraction efficiency at 555 nm) and reflectivity (70%). SLM’s non-modulating portion (13%) leads to unwanted zero-order that can be avoided by 16-level blazed grating. The estimated RMS error in addressing a 4-mm multifocal phase pattern on the SLM (500 x 500 pixels) due to phase wrapping and limited pixel resolution is 0.02 µm, 0.06 µm and 0.04 µm for diffractive trifocal, refractive bifocal and EDOF IOLs. Use of 250 x 250 pixels alone results in TF VS RMS difference of 0.01. SimVis allows high light efficiency (96%) binocular see-through experience. To achieve TF VS RMS difference lower than 0.03, it needs 6, 13, 19 time coefficients for diffractive trifocal, refractive bifocal and EDOF IOLs. Reduction in pupil size from 4-mm to 3-mm causes TF VS RMS difference of 0.05 for trifocal diffractive IOL, though a look-up table of time coefficients for different pupil sizes nullifies this effect in SimVis. Also, the corneal aberrations affect the tunable lens based simulator in a similar manner as they affect SLM based simulator and real IOLs.
Simulations suggest that SimVis offers a light efficient, less bulky and sufficiently accurate solution in comparison with the SLM based simultaneous vision simulators.
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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