Aspheric IOL brings benefits of being aberration-free

The aberration-free aspheric IOL is a three-piece foldable IOL with PMMA haptics. Its optic is made from a third-generation silicone, has square edges, and is constructed so that its power is equally distributed from the center to the periphery on both the anterior and posterior surfaces. Therefore, it is truly an aspheric lens.

"I think this advanced IOL is going to raise the bar in the field of implant surgery toward achieving higher quality of vision, just as we have seen the target raised in keratorefractive surgery," said Dr. Nichamin, medical director, Laurel Eye Clinic, Brookville, PA.

Design rationale With the focus of cataract surgery outcomes shifting from simply attaining an emmetropic result to achieving better quality of vision, implant engineers and designers have been striving to come up with innovative lens designs to fulfill that goal. The first product available was the modified prolate IOL featuring a negative spherical asphericity on its anterior surface (Tecnis, AMO). In contrast to standard spherical IOLs that impart positive spherical aberration, the modified prolate implant was designed to be an improvement by compensating for the positive spherical aberration of the average cornea (Tecnis, AMO).

Consequently, patients without "average" corneal asphericity may not be optimal candidates for that implant, and if the lens tilts or decenters in any eye, there is the potential for induced higher-order aberrations and worsened quality of vision. Although problems with post-implantation lens malpositioning are uncommon with modern surgery, they are not impossible, and there is particular concern in patients with pseudoexfoliation or who have weak zonules for other reasons, Dr. Nichamin observed.

He added that studies of the effects of decentration use the center of the pupil as a gauge. However, the center of the pupil is usually not coincident with the visual axis, and patients with a large angle kappa may experience induced aberration even with a perfectly centered modified prolate IOL or conventional lens.

"Compared with conventional IOLs, the aspheric IOL reduces induced spherical aberration in all eyes, and in contrast to the modified prolate IOL, the aspheric IOL is appropriate for all patients irrespective of their corneal asphericity while also being neutral in regard to avoiding induced aberration following tilt or decentration," Dr. Nichamin said.