Troutman Award winner's focus is on wavefront findings

Dr. Netto is currently in the cornea and refractive surgery department, University of São Paulo, Brazil. He conducted the study while completing a 3-year fellowship under the direction of Steven Wilson, MD, at the University of Washington, Seattle, and The Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, OH.

Using a particular system (WaveScan WavePrint,VISX/Advanced Medical Optics), Dr. Netto and colleagues measured aberrations in 418 eyes of 226 consecutive patients seen at the Refractive Surgical Center of the University of Washington. The study population had a mean age of about 43 years, included a slight majority of men (53%), and had a mean spherical equivalent (SE) of –3.4 D.

The results showed that although defocus and astigmatism were the predominant aberrations in these patients, the surgical candidates had significant amounts of higher-order aberrations (HOAs), particularly coma, trefoil, and spherical aberration. The amount of HOAs increased with increasing pupil size and with patient age, especially once patients reached the fifth decade of life. However, it was not significantly related to patient gender or SE.

"Previous studies had established the wavefront aberrometer as a valid diagnostic tool and reported wavefront data from pathologic corneas as well as outcomes of conventional treatment. Through that research, wavefront technology changed our understanding of visual optics and enabled the development of new excimer laser platforms to correct lower- and higher-order aberrations. However, information was limited about the HOAs in the population of normal eyes of subjects presenting for refractive surgery," said Dr. Netto, explaining the rationale for the published study.

Eyes were selected for inclusion if they had no history of ocular trauma or surgery, a best spectacle-corrected visual acuity of 20/20 or better, and absence of any topographic abnormalities. The wavefront measurements were obtained in a dark room before cycloplegic drops were administered and using three different wavefront apertures.

At the largest pupil aperture (6.0 mm), total mean ± SD HOA RMS was 0.23 ± 0.11 µm (range, 0.03 to 0.65 µm). The most frequent HOAs were coma (mean, 0.14 ± 0.08 µm; range, 0.01 to 0.48 µm), trefoil (mean, 0.10 ± 0.07 µm; range, 0.0 to 0.43 µm), and spherical aberration (mean, 0.09 ± 0.07 µm; range, –0.04 to 0.39 µm).

Data accuracy

The study also was designed to investigate the accuracy of refractive data derived using the wavefront aberrometer by comparing it with values obtained from manifest refraction performed with a phoropter.

Based on the results, the investigators concluded that wavefront analysis could be a useful tool for objectively measuring preoperative refractive error, although they noted that there were significant disparities between the two measurement techniques in a few patients.

Discussing wavefront-guided surgery, Dr. Netto observed that it is difficult to try to compare the efficacy of different laser platforms for correcting HOAs.

Although results from the FDA clinical trials may be considered to offer the best datasets, no conclusions can be derived from comparisons based on those outcomes because the various studies differed with respect to a number of design issues. These issues involved inclusion criteria, range of attempted correction, duration of follow-up, offset and nomogram adjustments, and visual function assessments.

"All currently available platforms provide excellent outcomes, and in clinical practice, the key factors that influence the results are the experience of the surgeon and nomogram adjustment," Dr. Netto said.