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5 Supported by an unrestricted educational grant from Abbott Medical Optics by Steven Schallhorn, MD Experiencing the significant impact of LASIK versus surface ablation visual advantage in the early postopera- tive weeks (1 day postop, 72% of those having LASIK had 20/16 UCDVA vs. 9% of those with PRK; 1 week, 78% of those with LASIK vs. 36% of those with PRK; 1 month, 84% of those with LASIK vs. 63% with PRK). Three months after surgery, 20/16 UCDVA was achieved in 85% of those having LASIK versus 83% of those having PRK. PRK and whether we are maximizing the benefits of LASIK. Visual acuity We recently conducted a retrospective study of 1,007 patients (1,846 eyes) who had PRK and matched them to 22,866 patients (44,475 eyes) who underwent LASIK. When we examined the percentag- es of patients achieving 20/16 uncor- rected distance visual acuity (UCDVA), patients who had LASIK showed a clear Surgeons may have misperceptions regarding the value of surface ablation in particular cases F or a segment of our refractive surgery patients, concerns of dry eye may influence surgeons to choose surface ablation over LASIK. While it may come as no surprise that patients who have LASIK have a higher satisfaction rate early after surgery and faster visual recovery, there are less, not more, dry eye issues with LASIK. Therefore, some may wonder whether we are being overly cautious in opting for Topography-guided ablations Topography-guided corrections combine corneal topography with manifest refrac- tion, using Placido disk and Scheimpflug technology. The system measures 22,000 to 25,000 elevation points, and the abla- tion profile is based on the entire corneal shape (Figure 2). The surgeon can specify centration, adjust postoperative corne- al asphericity, and choose the desired refractive correction. One advantage of this system is that surgeons are familiar with topography. It is not influenced by accommodation or centroid shift. We can also consider angle kappa. It is designed to address corneal aberrations exclusively in primary eyes and therapeutic cases. It can be used in cases where the corneal aberrations are too high for accurate wavefront capture or in circumstances where the surgeon would not want to use wavefront-guided ablation, especially with older wavefront systems or in cases with previous corneal surgery such as penetrating keratoplasty, corneal scars, and keratoconus in con- junction with collagen crosslinking. Unmatched customization Advanced wavefront-guided ablation and topography-guided ablation offer an unprecedented level of customization. I have seen a number of patients with highly aberrated eyes who have been treated with topography-guided ablation to regularize their corneas. Six months later we imaged and treated them with wavefront-guided ablation to treat the remaining refractive error and have achieved excellent refractive outcomes. These higher-resolution diagnostics deliver higher-quality vision in virgin and highly aberrated eyes. The next step is to adopt this technology and define measurement standards to achieve these results. Dr. Manche is professor of ophthalmology and director of the cornea and refractive sur- gery division, Byers Eye Institute, Stanford School of Medicine, Calif. He can be contact- ed at edward.manche@stanford.edu. continued from page 4 continued on page 6 " Surface ablation plays a key role in treating specific patients, but misperceptions, including concerns about dry eye, may drive surgeons to choose PRK over LASIK. " –Steven Schallhorn, MD

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