San Diego-A laboratory comparison of the theoretical optical performance of three different IOLs conducted under similar intraocular conditions indicated that the aberration-free IOL (L161AO, Bausch & Lomb) was superior to the conventional IOL (L161U, Bausch & Lomb) in optical performance under all conditions. It was superior to the modified prolate aspheric IOL (Tecnis Z9000, Advanced Medical Optics) in various degrees of decentration, and it maintained optical performance in various simulated clinical conditions.
Jay Pepose, MD, PhD, and colleagues described this study at the American Society of Cataract and Refractive Surgery annual meeting. The IOLs were analyzed using:
"The conventional IOL has reduced optical performance because it adds to the positive spherical aberration of the eye. An aberration-free IOL does not add to nor subtract from corneal spherical aberration," he said.
"The modified prolate aspheric lens was slightly superior to the other lenses. The aberration-free lens was better than the conventional IOL," explained Dr. Pepose, professor of clinical ophthalmology and visual sciences, Washington University School of Medicine, and director, Pepose Vision Institute, St. Louis. "However, all of the lenses demonstrated very good optical performance."
Lens decentration issues Differences in the lenses were seen when there was 0.5 to 1 mm of decentration. The investigators found that the aberration-free IOL has a much higher modulation transfer function at all spatial frequencies compared with the conventional IOL or the modified prolate aspheric IOL.
"At 0.5 mm of lens decentration, the modified prolate aspheric IOL was somewhat better at the lower spatial frequencies than the conventional IOL, but worse at the higher spatial frequencies compared with the conventional IOL," Dr. Pepose reported. "This may be the reason that the contrast sensitivity data are better but the visual acuity is not better in some of the clinical reports. However, the aberration-free IOL was superior to the other two lenses. Even at 1 mm of decentration the aberration-free IOL outperformed the conventional IOL that was centered perfectly."
With a 4-mm pupil, the effects of decentration are even more pronounced. A modified prolate aspheric IOL that was well-centered performed better than the aberration-free IOL and was far superior to the conventional IOL. However, when the lenses were decentered by 0.5 to 1 mm, the aberration-free lens outperformed the modified prolate aspheric lens. He pointed out that there was some splaying of the curve between tangential and sagittal views because non-axisymmetrical aberrations, such as coma and astigmatism, were induced when the decentered lenses had either positive or negative inherent spherical aberrations. There was no splaying of the curve with an aberration-free IOL because it is immune to the adverse optical effects of decentration.
"In this experiment in which we simulated variations in pupil size and decentration, the aberration-free IOL demonstrated higher optical performance compared with the conventional IOL under all conditions," Dr. Pepose concluded. "It demonstrated higher optical performance compared with the modified prolate aspheric IOL under conditions of decentration, particularly with decentration of 0.5 mm or greater, and it maintained optical performance in various simulated clinical conditions."