By revealing that the first generation of LASIK procedures were inducing higher-order aberrations (HOAs), wavefront technology answered a key question about why outcomes had been less than perfect. At the same time, it raised a new question: How best to use that information to improve outcomes? In response, two different approaches, wavefront-guided (WFG) treatments and wavefront-optimized (WFO) treatments, emerged. So far, the FDA has approved three laser systems for WFG treatments: Alcon's CustomCornea, Advanced Medical Optics' CustomVue, and Bausch & Lomb's Zyoptix. In 2003, the agency approved one system for WFO treatments: WaveLight's AllegrettoWave.
The availability of both approaches leaves refractive surgeons wondering which is better for their patients. While no large-scale, true head-to-head comparison has been done, the results of individual FDA clinical trials, studies performed more recently, and insights from surgeons who are familiar with both approaches can help to clarify the differences.
How the approaches differ
In contrast to WFG treatments, the WFO treatment does not attempt to correct or reduce any pre-existing HOAs. Instead, it is designed to prevent the induction of one HOA, spherical aberration. Of all the HOAs, first-generation treatments induced spherical aberration most prominently, causing glare, halos, and blurred vision for some patients, especially in dim light conditions. The theory behind the WFO treatment is that 80% to 90% of patients do not have a substantial amount of preoperative HOAs and therefore benefit more from a treatment that preserves their existing quality of vision. The theory further holds that WFG treatments are only necessary for the small percentage of patients with certain preoperative visual symptoms.
Are results equivalent?
Proponents of WFG treatments say that the problem with addressing only one HOA is that many aberrations pre-exist or are induced by treatment. They say that the aberrations are known to diminish vision quality, and a treatment that does not take care of them is not the best treatment possible, nor is it truly customized to an individual eye.
"Theoretically, why would you not treat all of an eye's distortions?" asked Daniel S. Durrie, MD. "In some patients, 98% of the correction might be lower-order. For them, there should be no difference in results with a wavefront-guided or a wavefront-optimized treatment.
"However, at least 80% of eyes have some level of HOAs, and in the FDA clinical trials of the three wavefront-guided treatments, all produced better outcomes than their corresponding conventional treatments even in patients with low preoperative levels of HOAs."