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Toshifumi Mihashi, James Wolffsohn, Takahiro Hiraoka, Sandeep Dhallu, Yoko Hirohara, Masashi Nakajima, Tetsuro Oshika; Shack-Hartmann wavefront aberrometer with ray based analysis for measuring bifocal lenses. Invest. Ophthalmol. Vis. Sci. 2017;58(8):339.
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© ARVO (1962-2015); The Authors (2016-present)
Several studies suggest that bifocal intraocular lenses(IOLs), such as Oculentis bifocal IOL, have larger depth of focus than monofocal IOLs. But, wavefront analysis with typical low order Zernike polynomial expansion may not be suitable for evaluating the eye with segmented bifocal IOL in which the wavefront has discontinuity at the boundary between the two power level areas. A ray based method for analyzing the output from a Shack-Hartmann wavefront aberrometer (SHWA) to better assess the double foci in bifocal IOLs was investigated.
A bifocal artificial eye (prototype, University of Tsukuba, Japan), a toric IOL (SN6AT5, Alcon, TX), and a bifocal segmented IOL （Lentis Mplus LS-312 MF15, Oculentis, Germany）was measured using an SHWA (prototype, Topcon, Japan). A wavefront sensor of the SHWA detected the slight local deviations at the foci of the lens array. To analyze the data, a ray based method instead of the conventional standard analysis method with the low order (typically up to 6th order) Zernike polynomial expansion was used. In the ray based method, the data from the wavefront sensor were interpreted as ray vectors instead of wavefront aberrations in the conventional method. The ray transfer equations to form spot diagrams at multiple though focus points were calculated using the measured ray vectors. The point at which the spot diagram standard deviation (SD) was minimum in all the though focus points was regarded as a focal point. The minimum SD was evaluated over each power level area for the bifocal lenses. Vertical and horizontal SDs were evaluated for the toric IOL.
High contrast spot diagrams from the three lenses were achieved and measured. The difference between the two foci for the bifocal artificial eye was 2.04 diopter (D) and its design value was 2.28 D. For the toric IOL, astigmatism was 1.97 D and its catalog value was 2. 28 D. The difference between the two foci for the bifocal IOL was 1.59 and its catalog value was 1.5 D.
The measured value for the artificial eye and the toric IOL were 10% smaller than the nominal values. Considering this method had not been specifically calibrated before the measurements and the reasonable observation of spot diagrams, the method has potential to evaluate refractive powers of bifocal IOLs.
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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