Posterior aspheric surface of lens helps improve image quality

May 15, 2007

A newer-generation IOL reduces higher-order, spherical, and trefoil aberrations when compared with the previous-generation lens. This reduction in higher-order aberrations may result in better outcomes for patients, specifically, improved contrast sensitivity, reduction in night vision disturbances, and improved visual performance compared with conventional spherical IOLs.

Key Points

Dr. Braunstein presented his group's findings with the newer-generation IOL here at the American Academy of Ophthalmology annual meeting.

"The goal of modern cataract surgery," Dr. Braunstein stated, "is to help the patient achieve the best quality of vision possible. Conventional spherical IOL implants have been shown to increase positive spherical aberration (SA) as the result of marginal light rays coming into focus in front of paraxial light rays. Increased SA can result in reduced visual function and worsened contrast sensitivity. The [new] IOL differs from conventional spherical IOLs in that it has a posterior aspheric surface designed to improve image quality by merging the marginal and paraxial light rays."

He and colleagues Ankoor Shah, BS, and Kira Manusis, MD, from Columbia University Medical Center and the New York Eye & Ear Infirmary, respectively, studied the HOAs resulting from the implantation of the newer IOL compared with its predecessor in patients undergoing cataract surgery.

The HOAs in all eyes were measured using a particular aberrometer (iTrace, Tracey Technologies). This aberrometer, Dr. Braunstein said, uses the principle of ray tracing, i.e., measurement of incoming parallel rays of light (256 rays) as they pass through the optical system of the eye and form spot images on the retina. The rays enter the entrance pupil sequentially, and each retinal spot is measured separately.