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K. Ohnuma, T. Noda, K. Negishi; Design and Optical Performance of a New Diffractive Multifocal IOL With Additional Spherical Aberration . Invest. Ophthalmol. Vis. Sci. 2006;47(13):321.
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To evaluate the optical performance of a new diffractive multifocal intraocular lens (IOL) by changing the positions of the two main focal points and adding spherical aberration to determine the best design for obtaining broader depth of field and higher image contrast than with conventional multifocal IOLs.
In the new design, spherical aberrations were added to the two main focus points at distance and near to obtain broader depth of field and higher image contrast than conventional multifocal IOLs. To determine the amount of spherical aberrations to add, the images of Landolt’s ring (logMAR 0.4) were computer simulated using various combinations of the two focus points and additional positive/negative spherical aberrations with pupil diameters of 2, 3, 4, and 5 mm. The contrast of each simulated image was calculated using our original software. The corneal spherical aberration was included in the spherical aberration of the IOL.
The best design with the broadest depth of field and the highest image contrast seemed to have not only two focal points at 0.75 diopter (D) (distance) and 1.25 D (near) with equal diffraction efficiency but also additional negative spherical aberration at the far focal point and additional positive spherical aberration at the near focal point. The depth of field, that is, the range at which the image contrast exceeds 60%, was 2 D with the 2–mm pupil diameter. This design maintained good or fair image contrast with the other pupil diameters. These results suggest that this design could provide good vision from infinity to 50 cm during the day and acceptable vision at night.
Computer simulation provided a good design for a diffractive multifocal IOL with additional spherical aberration. However, this method included the corneal spherical aberration in that of the IOL. Further investigation is needed to determine the best design by eliminating the effect of the corneal spherical aberration using data from an average cornea.
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