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Corneal Topography in Modern Refractive Surgery

Over the last two decades, refractive surgical methods have evolved rapidly, owing in large part to the role played by modern corneal topographical analysis. Studies of early procedures, such as epikeratophakia and photorefractive keratectomy (PRK), showed that treatment zones were often small and could be markedly decentered so that significant areas of untreated cornea overlay the apparent entrance pupil of the eye. Such conditions led to visual complaints of halos, glare, and reduced contrast. In other early work, irregularities in the treatment zone, such as central islands, were discovered with corneal topographical analysis following PRK for myopia, and the means to avoid these, such as altered algorithms and scanning laser systems, were developed. The traditional yardsticks for the efficacy of specific refractive surgeries have been uncorrected and best corrected visual acuities and cycloplegic and manifest refractions. Even today, corneal topography analysis is not often considered a primary outcome measure for clinical trials. Corneal topographers are now the standard of care only for preoperative screening of refractive surgical candidates, although they are used in the qualitative analysis of postoperative results to pin down causes of reduced vision after eventful refractive surgery. In this chapter, both preoperative and postoperative use of corneal topography in modern refractive surgery will be explored, with close attention paid to clinical application. In particular, guidelines will be summarized to help to differentiate the normal from the abnormal cornea (relevant to preoperative refractive surgical screening) and to demonstrate the difference between optimal and suboptimal postoperative results in modern refractive surgery. Special attention to preoperative screening is given because of the urgent need—particularly for laserassisted in situ keratomileusis (LASIK)—for surgeons to be aware of the