Wavefront-Guided LASIK Nomogram Improves Myopia Outcomes

Lara C. Pullen, PhD

November 15, 2012

CHICAGO — A new LASIK nomogram uses the least complicated approach to predict improvements in outcomes, according to new research.

Steven C. Schallhorn, MD, chief medical director for Optical Express in the United Kingdom, presented the comprehensive model here at the American Academy of Ophthalmology 2012 Annual Meeting.

It was developed using iterative statistical modeling that balances potential outcomes with ease of use, and is based on a substantial dataset of wavefront-guided (WFG) procedures.

The dataset was obtained by searching the Optical Express database for patients who underwent a primary WFG LASIK procedure to correct myopia in 2010. The search yielded 61,543 consecutive procedures.

When developing the nomogram, the team used linear/nonlinear regression, parametric/nonparametric regression, robust regression, Bayesian probability, and weighted least squares regression.

Independent variables were also evaluated, 2 of which had notable univariate significance: age (stratified) and sex (high interaction with age). "We have so much data that we can stratify the data to understand where there is bias and where there isn't," Dr. Schallhorn reported.

Different nomogram models were developed through an iterative process that considered all significant variables. The models were then used to predict outcomes. The most comprehensive model was named model B; it was estimated to improve refractive accuracy by 87.5% (3-month manifest spherical equivalent within 0.50 diopters). The simpler model C predicted an 87.4% improvement, so was considered to be almost as good as the more complex model B.

Model C consisted of 3 steps: selecting a wavefront capture with the sphere within 0.75 diopters of manifest; adjusting to match the treatment sphere to manifest; and boosting by +5%. Model C was used as the nomogram and was tested on patients from January to June 2012. One-month outcomes were evaluated. During this time, primary WFG LASIK was performed on 25,412 eyes (12,966 patients). "We achieved actually better than we expected," Dr. Schallhorn explained.

Session moderator Karl G. Stonecipher, MD, director of The Laser Center in Greensboro, North Carolina, said "you've got to applaud these guys.... Wouldn't it be great if we could put our 1-month data in a box and do this?"

Dr. Schallhorn explained that the best outcomes occur in young patients who are myopes. He hopes that the nonogram will help them to get the best outcome for each stratified group. For example, the higher the level of myopia, the more variance there is in outcome; it is important to reduce that variance.

One specific improvement with the nomogram was in astigmatism correction. Dr. Schallhorn reported that the old WFG did an undercorrection of astigmatism. The nomogram was able to improve the outcome.

Dr. Schallhorn reported that the nomogram resulted in the same delta of improvement for photorefractive keratectomy as it did for LASIK, although he did not present those data. He noted, however, that the techniques are used on different patient populations.

Dr. Schallhorn reports being a consultant for AMO. Dr. Stonecipher reports being a consultant for multiple ophthalmological companies.

American Academy of Ophthalmology (AAO) 2012 Annual Meeting: Abstract PA020. Presented November 11, 2012.

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