Wavefront optimized profile offers excellent results

February 15, 2005

New Orleans—Incorporating higher-order aberrations (HOAs) into LASIK treatment performed with aspherically optimized profiles using the MEL80 excimer laser (Carl Zeiss Meditec) increases treatment benefit without compromising refractive accuracy, said Dan Z. Reinstein, MD, MA (Cantab), FRCSC, at the ISRS subspecialty day meeting.

He presented 6-month follow-up results from a prospective, paired-eye comparison study of 25 consecutive patients who were treated for low to moderate myopia (-1.75 to -7.50 D) and astigmatism up to -1.50 D. To be eligible to participate, patients had to have an interocular spherical equivalent (SE) difference of less than 0.75 D.

Wavefront measurements were obtained using the WASCA Aberrometer (Carl Zeiss Meditec). The CRS-Master platform (Carl Zeiss Meditec) was used to integrate the data into the standard optimized aspheric profiles (SOAP) for sphere and cylinder to produce a wavefront optimized profile (WOP).

The results showed the two protocols were associated with similarly excellent treatment precision, efficacy, accuracy, and safety. However, there was a benefit for the WOP approach for minimizing induced spherical aberration and that seemed to translate into a benefit of significantly better mesopic contrast sensitivity.

"In context of the fact that these were normal eyes with only minimal levels of higher-order aberrations and considering that mesopic contrast sensitivity testing is not a highly reproducible test, these findings demonstrate that there seems to be an advantage to using wavefront-guided treatment over and above aspheric profiles alone," Dr. Reinstein said.

"And, we expect that the favorable differences associated with the WOP technique would be even more marked in eyes that present with more significant aberrations," said Dr. Reinstein.

Dr. Reinstein is medical director, London Vision Clinic, England, and assistant professor, clinical ophthalmology, Weill Medical College of Cornell University, New York.

He added this is the first demonstration that application of the HOAs results in superior outcomes compared with treatment using an aspheric profile. Therefore, this study's findings refute claims that maximum benefit can be achieved using an aspheric profile alone.

State-of-the-art technology The unique ability to achieve a benefit over and above wavefront optimization using the Carl Zeiss Meditec system can be explained by the fact that the high-resolution wavefront technology is truly state-of-the-art, Dr. Reinstein said.

"Degradation of the accuracy of sphere and cylinder correction with the introduction of higher-order aberrations into the ablation profile has been a problem with other systems, but we found it was not the case using this advanced platform. We believe the high resolution of the WASCA wavefront sensor, extreme accuracy of the CRS-Master, and the highly stable energy delivery of the MEL80 laser allowed us to show a difference between treatment with an aspheric profile and an aspheric profile with wavefront optimization where others could not," he commented.

Mean preoperative SE for the 50 eyes included in the study was -3.75 ± 1.80 D and mean cylinder was -0.55 ± 0.40 D. Mean (SD) higher-order RMS HOAs for third- and fourth-order Zernike coefficients were 0.44 ±0.1 µm.

Treatment precision was analyzed using the Pearson correlation coefficient from a linear regression for the plot of attempted SE change versus achieved SE. Pearson correlation coefficients were 0.97 for eyes that underwent correction using the aspheric profile only and a virtually identical 0.96 for those treated with the higher-order wavefront components added.