SPOTLIGHT ON TECHNOLOGY & TECHNIQUE

Nidek CATz system marries topography with LASIK treatment

Topographic data with custom ablation planning software can help customize outcomes.

By Bill Kekevian, Senior Associate Editor

As George O. Waring, III, MD, FACS, explains it, LASIK outcomes are not solely a matter of visual acuity. Just as important is improved visual quality. To that end, Dr. Waring, an emeritus clinical professor at Emory University in Atlanta, has worked as a consultant and investigator for Nidek.

One key to attaining high-quality results involves gathering as many data points as possible to predict visual outcomes, he says. From that data, Nidek has developed the recently FDA-approved Customized Aspheric Treatment Zone, or CATz, for its NAVEX Quest, EC5000 CXIII excimer laser system, which couples with the OPD-Scan II — a combination topographer, refractometer and wavefront aberrometer.

A SINGLE TREATMENT ZONE

CATz utilizes the Nidek Final Fit software to gather measurement points that provide a topography-assisted correction unique to the individual patient. CATz uses the Quest Excimer to create a single treatment zone.

“The distinction between an optical zone and a transition zone is not useful because we treat an 8.5-mm treatment zone; the whole area is an aspheric uniform treatment area,” Dr. Waring says. “The instrument measures the cornea, like a topographer would, creates an elevation map (which other topographers can do as well), but then uses that map as a guide with Final Fit Custom Planning to treat the whole 8.5-mm ablation.”

SYMMETRIZING

“The more symmetrical the cornea, the better the optics,” Dr. Waring says. “If you have a cornea that has astigmatism or significant coma aberration, you will have a distorted optical result. If you render the cornea symmetrical, you create a better optical image.”

POTENTIAL ADVANTAGES OVER WAVEFRONT

The topography-guided CATz treatment differs from wavefront-guided treatments in that “it’s based on the actual cornea shape,” Dr. Waring says. Not only can topographers measure a wider area on the cornea than wavefront, which is limited by pupil diameter, but they can also accurately measure highly aberrated eyes, he adds.

“The topography measurements indicate how asymmetrical the cornea is, and then the Final Fit software produces a topographic map of the desired more symmetrical outcome,” he says.

The OPD can convert this to refractive outcome and analyze the quality of vision as the point spread and modulation transfer functions. Point­‐spread function presents the simulation of how a point of light images onto the patient’s retina.

This assessment, Dr. Waring says, helps evaluate the likelihood of nighttime glare or halos. “If the picture is just a pinpoint, that’s what you want; you want no distortion,” he says. “But if it looks like a comet or like Saturn, with rings around it, you know that the quality of vision is not optimal.” OM