However, these “higher order aberrations” account for only a small amount (probably no more than 10%) of the total refractive error of the average person's eye. Conventional Lasik increases higher order aberrations. Although wavefront-guided treatments attempt to eliminate higher order aberrations, results from the clinical studies have shown that the average aberrations still increase, but less than they do after conventional Lasik. In a few studies comparing wavefront-guided Lasik to conventional Lasik, a slightly larger percentage of subjects treated with wavefront Lasik achieved 20/20 vision without glasses or contact lenses compared to subjects treated with conventional Lasik. Patient selection and the experience and competence of the surgeon are still the most important considerations.