Surgeons weigh WFG ablation

October 22, 2011

Leading refractive surgeons agree wavefront-guided ablation is a significant advance in laser vision correction, but have different opinions about its role in treating myopic eyes with low higher-order aberrations.

Orlando-Leading refractive surgeons agree wavefront-guided (WFG) ablation is a significant advance in laser vision correction, but have different opinions about its role in treating myopic eyes with low higher-order aberrations (HOAs).

Ronald Krueger, MD, explained why he believes WFG ablation has no measurable advantage in these cases, defined as having total HOA RMS < 0.3 μm. Steven C. Schallhorn, MD, presented evidence supporting its use.

Dr. Krueger, medical director, refractive surgery, Cole Eye Institute, Cleveland Clinic, Cleveland, OH, noted that the outcomes of a WFG treatment depend strongly on having a reliable wavefront measurement, perfect centration, and perfect eye-tracker performance. However, cyclorotation of more than 2° can occur in about two-thirds of patients and failure of iris recognition and iris tracking are also relatively common.

Both of these issues make perfect centration difficult, Dr. Krueger said.

He also presented data from a study he performed using adaptive optics that showed HOA < 0.3 μm are not visually significant along with evidence that for ideal visual performance, HOAs, should be optimized to maintain a prolate cornea, rather than minimized. This latter outcome can be achieved with a wavefront-optimized (WFO) ablation profile.

Finally, results of multiple comparative studies as well as a recent meta-analysis including 930 eyes from seven studies show no differences in refractive and visual acuity outcomes comparing groups of eyes with low levels of HOA undergoing WFG versus WFO ablation.

“These papers found that WFG is important in eyes with more than 0.3 μm HOA, but it has no benefit over WFO for the myopic eye with HOA < 0.3 μm,” Dr. Krueger said. “In fact, in eyes treated for higher levels of myopia, there is some induction of spherical aberration, especially when the profile is not WFO. Therefore, I believe WFO should be used in eyes with low HOAs, and specifically in higher myopes.”

In his discussion, Dr. Schallhorn, global medical director, Optical Express, presented study data showing that differences can be detected favoring WFG versus WFO ablation in eyes with low levels of HOA. For example, in a study by Tanzer et al. that evaluated a number of different endpoints, differences were found in very fine levels of uncorrected visual acuity (UCVA), mesopic 25% contrast acuity, and induction of HOA. Manche et al. also reported that at 12 months, WFG treatment was associated with better 25% mesopic contrast acuity, better UCVA, and greater patient preference than WFO ablation.

“The WFG treatment induces less HOA than WFO ablation and that gives advantages,” Dr. Schallhorn said. “Granted, they are subtle and may not show up in refractive outcomes or even in UCVA. However, they are detected in more sensitive measures of visual function, such as contrast sensitivity, or what I collectively call quality of vision.”

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