MAY 2013

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

Issue link: https://digital.eyeworld.org/i/129516

Contents of this Issue


Page 77 of 86

Update on the latest in refractive cataract techniques and technologies 7 Improving analysis and treatment of astigmatism with LASIK by Steve Schallhorn, MD A new wavefront-guided system is producing strong results out of the box, before optimization W avefront aberrometers have provided refractive surgeons the ability to measure and treat more ocular aberrations and give our patients better outcomes. We have 20 surgical centers, each of which has wavefront aberrometry. While wavefrontguided ablations have improved outcomes to very high levels, treating precise levels of astigmatism axis and magnitude is an area where we can make incremental improvements. We evaluated a new aberrometer (iDesign, Abbott Medical Optics, Santa Ana, Calif.) in 282 eyes (149 patients) who underwent LASIK between May 30, 2012 and August 19, 2012 in one of our centers and compared results to 18,866 eyes (8,657 patients) who underwent LASIK during the same time period at the remaining 19 centers with our current wavefront aberrometer. We matched the two groups for age and refractive error (sphere and cylinder). Our current wavefront-guided LASIK is finely tuned and finely honed. We have undertaken a very comprehensive nomogram development and analysis over the last several years, starting almost five years ago. This evaluation consisted of more than 65,000 treatments and included one, three, and six month follow-up. We create a nomogram adjustment and then look at how well our adjustment performed and readjust when necessary. In other words, our current system represents the penultimate formulas after five years of intense evaluation and re-evaluation. Because astigmatism has magnitude and direction, cylinder correction needs to be analyzed using vector analysis; if the preop astigmatism was 1.0 D axis 180 and postop is 1.0 D axis 090, the magnitude of cylinder alone suggests no change. In reality, though, the cylinder was significantly overcorrected because of the change in axis. Figure 1 shows very tight results with both systems. When we looked at intended refractive change versus the surgically induced refractive change in cylinder, better cylinder outcomes with the iDesign over our current system become apparent (Figure 2). The correlation coefficient (r2) is closer to 1 (ideal) with the iDesign compared to the current system. Figure 3 illustrates similar cylinder outcomes in terms of the ratio of attempted vs. achieved cylinder continued on page 9 Figure 1. At one month, the manifest spherical equivalent results with the new wavefront-guided system are essentially equivalent to a wavefront-guided system with years of use and optimization. New vs. current A review of the data shows that the iDesign immediately "out of the box" without the benefits of years of refinements produces similar or better outcomes as our current wavefront system (Figure 1). There are two distinct lessons here: Our current outcomes are exceptionally good, and the out-of-the box iDesign results are equally impressive. Figure 2. In this comparison of intended cylinder correction vs. surgically induced refractive change in cylinder, the new wavefront-guided system results in less undercorrection and a tighter distribution of outcomes. Steve Schallhorn, MD " The new aberrometer produces results at least as good as what we are currently using—and that system has undergone years of analysis and refinement. "

Articles in this issue

Archives of this issue

view archives of Eyeworld - MAY 2013