Griffith E. Altmann

Optical performance of 3 intraocular lens designs in the presence of decentration

Purpose: To study the theoretical optical performance of 3 intraocular lens (IOL) designs in the presence of IOL decentration. Setting: Optics Center, Bausch & Lomb, Rochester, New York, USA. Methods: A ray‐tracing program was used to evaluate the effect of IOL decentration on the optical performance of 3 silicone IOLs (LI61U, Bausch & Lomb; Tecnis Z9000, Advanced Medical Optics; and a new aberration‐free IOL [SofPort AO, Bausch & Lomb]) in an experimental model eye. The study was done using pupil diameters of 3.0 mm, 4.0 mm, and 5.0 mm and IOL decentrations of 0 mm, 0.25 mm, 0.50 mm, 0.75 mm, and 1.00 mm. The modulation transfer functions were computed and plotted. A Monte Carlo simulation analysis with 1000 trials with IOL decentration randomly varying for each pupil size was performed. Results: Decentration of LI61U and Tecnis Z9000 IOLs led to asymmetrical higher‐order aberrations that adversely affected the optical performance of the model eye; performance was not affected with the aberration‐free IOL because it lacks inherent spherical aberration. Optical performance with the aberration‐free IOL was better than with the LI61U IOL as the former has less spherical aberration and did not introduce other aberrations when decentered. Performance with the aberration‐free IOL was better than with the Tecnis Z9000 IOL for 3.0 mm, 4.0 mm, and 5.0 mm pupils when decentration exceeded 0.15 mm, 0.30 mm, and 0.38 mm, respectively. Performance with the LI61U IOL was better than with the Tecnis Z9000 IOL for 3.0 mm, 4.0 mm, and 5.0 mm pupils when decentration exceeded 0.3 mm, 0.5 mm, and 0.5 mm, respectively. Monte Carlo simulations showed the expected postoperative results of the LI61U IOL and aberration‐free IOL would be repeatable and predictable, whereas the outcomes with the Tecnis Z9000 IOL would vary widely. Conclusions: The optical performance of the model eye was not affected by decentration of an aspheric IOL designed to have no inherent spherical aberration. With decentration, the performance with the new IOL was better than with a conventional spherical IOL and an aspheric IOL designed to offset the spherical aberration of an average cornea.

Comparison of Through-Focus Image Sharpness Across Five Presbyopia-Correcting Intraocular Lenses

PURPOSE To assess through-focus polychromatic image sharpness of 5 FDA-approved presbyopia-correcting intraocular lenses (IOLs) through a range of object vergences and pupil diameters using an image sharpness algorithm. DESIGN Laboratory investigation. METHODS A 1951 USAF resolution target was imaged through Crystalens AO (AO), Crystalens HD (HD), aspheric ReSTOR +4 (R4), aspheric ReSTOR +3 (R3), and Tecnis Multifocal Acrylic (TMF) IOL in a model eye and captured digitally for each combination of pupil diameter and object vergence. The sharpness of each digital image was objectively scored using a 2-dimensional gradient function. RESULTS AO had the best distance image sharpness for all pupil diameters and was superior to the HD. With a 5-mm pupil, the R4 distance image sharpness was similar to the HD and at 6 mm the TMF was superior to the HD, R3, and R4. The R3 moved the near focal point farther from the patient compared to the R4, but did not improve image sharpness at intermediate distances and showed worse distance and near image sharpness. Consistent with apodization, the ReSTOR IOLs displayed better distance and poorer near image sharpness as pupil diameter increased. TMF showed consistent distance and near image sharpness across pupil diameters and the best near image sharpness for all pupil diameters. CONCLUSIONS Differing IOL design strategies to increase depth of field are associated with quantifiable differences in image sharpness at varying vergences and pupil sizes. Objective comparison of the imaging properties of specific presbyopia-correcting IOLs in relation to patients pupil sizes can be useful in selecting the most appropriate IOL for each patient.

Comparing pupil-dependent image quality across presbyopia-correcting intraocular lenses

Maxwell et al. report the AcrySof ReSTOR SN6AD3 aspheric diffractive multifocal intraocular lens (IOL) (Alcon, Inc.) has some superior optical properties (ie, modulation transfer function [MTF] and United States Air Force 1951 Resolution Target) demonstrated in distance optical-bench testing of 6 presbyopia-correcting IOLs, including the monofocal Crystalens accommodating IOL (Bausch & Lomb). Amultifocal IOL, which splits the light energy continuum between multiple foci and loses some energy to higher diffractive orders, outperforming a monofocal IOL is perplexing, especially considering (as the authors point out) that clinical studies contradict this finding. Recent studies show that despite the aspheric modification, the ReSTOR SN6A6D3 shows mesopic contrast sensitivity that remains comparatively decreased in many patients compared with contrast sensitivity in those with a monofocal IOL. Similarly, there has been no change in the U.S. Food and Drug Administration labeling of the aspheric ReSTOR warning about exercising caution when driving at night or under low visibility conditions, because some patients may have reduced contrast sensitivity under these conditions compared with those with monofocal IOLs. In reviewing the paper, the methods and study design have 2 limitations that should be addressed to place the findings in proper context. First, the authors chose to examine imaging performance through a 5.0 mm aperture at the IOL plane,