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Refractive Surgery | Feb 2011

The Achilles Heel of Customized Correction

The Zyoptix Advanced Nomogram compensates for aberration interaction.

There are encouraging developments in wavefront technology, suggesting that after 10 years of working with this medium it is finally giving us the type of results we had hoped for a decade ago. For instance, Suphi Taneri’s group in Münster, Germany, has demonstrated neutralization, and sometimes reduction, of higher-order aberrations (HOAs) and accurate correction of sphere and cylinder with the Technolas PTA Zyoptix LASIK system (Technolas Perfect Vision GmbH, Munich, Germany).

Historically, refractive surgeons have noticed problems with correcting HOAs. First, we are working with the oldest generation of wavefront sensors, some of which are more than a decade old, that were built by basic scientists who were unfamiliar with the complexity of clinical medicine. Second, when customized correction was originally done, we did not have active rotational eye trackers. In 2011, we have better understandings of wavefront sensors, active rotational eye trackers, and the interactions of aberrations, all of which facilitate the accurate correction of HOAs.

The PTA Zyoptix system combines an active rotational eye tracker, an accurate wavefront sensor, and an aspheric ablation profile that compensates for induced spherical aberration. The Achilles heel of customized correction has been unanticipated aberration interaction, which caused eyes with preoperative HOA to be under- and overcorrected postoperatively with regard to sphere and cylinder. Incorporation of the Rochester Nomogram, which Technolas calls the Advanced Nomogram, compensates for aberration interaction and makes the correction of sphere and cylinder extremely accurate, even when treating eyes with preoperative HOA. The Zyoptix PTA system effectively neutralizes HOA—and often reduces it—but does not compromise on correcting sphere and cylinder accurately. This is an exciting development that gives us the best of both worlds and improves optical quality for our patients.

Scott M. MacRae, MD, is a Professor of Ophthalmology and a Professor of Visual Science, Flaum Eye Institute, University of Rochester Medical Center, New York. Dr. MacRae states that he is a consultant to Bausch + Lomb and Technolas Perfect Vision and has disclosed a patent application on the Rochester Nomogram. He may be reached at tel: +1 585 273 2020; e-mail: scott_macrae@urmc.rochester.edu.