Determining intraocular lens power following corneal refractive surgery

Abstract

Corneal power after refractive surgery is difficult to assess, which makes it hard to calculate the appropriate intraocular lens power in the event that the patient needs cataract surgery later on. In the last 5 years, a variety of methods have been described to improve the accuracy of keratometric measurements in patients who have undergone corneal refractive corrections. We review the factors that make keratometric measurements inaccurate before discussing the traditional and novel methods developed to obtain reliable measurements in these patients. As patients who have undergone corneal refractive surgery get older, their chance of developing a visually impairing cataract increases. Unfortunately, the traditional methods used to measure corneal power (i.e., keratometry and videokeratography) are inaccurate after radial keratotomy, photorefractive keratectomy and laser in situ keratomileusis. This inaccuracy can easily lead to refractive surprises after phacoemulsification and intraocular lens implantation. For over 10 years, surgeons were obliged to rely on clinical history and contact lens over-refraction as the only methods to obtain a relatively predictable estimate of postrefractive surgery corneal power to be entered into intraocular lens calculation formulae. As interest in this topical issue continues to grow, more methods to accurately measure postrefractive surgery corneal power have been described. In addition, new technologies, such as the slit-scanning topography system (combined with Placido-disk videokeratography) and the rotating Scheimpflug camera, have been developed with the aim of determining the true corneal power after corneal refractive surgery.