Cataract Surgery Feature Story

NOVEMBER/DECEMBER 2012 CATARACT & REFRACTIVE SURGERY TODAY EUROPE 1 A ccuracy of biometric calculations and, more important, of refractive results depends on three main factors: preoperative biometric data including axial length, anterior chamber depth, lens thickness, and corneal curvature power variables; power calculation formulas; and quality and accuracy of the IOL. In the past 15 years, several million people worldwide have undergone various refractive surgery procedures for the most disparate visual defects. These patients will soon be candidates for cataract removal due to the natural aging process. In this population, corneal curvature is profoundly modified, and obtaining reliable biometry becomes complex. Additionally, patients who have previously undergone refractive surgery are accustomed to a high level of visual quality, translating to high expectations after cataract surgery. All available biometric devices, even the most sophisticated, are designed for use on normal prolate corneas, for which keratometry measurement based on 4 to 6 points is considered enough to accurately determine corneal curvature. These points are measured several millimeters from the corneal center; however, after refractive surgery, the corneal gradient changes dramatically across the corneal surface, from the pupil center to the periphery. The postoperative course may therefore be full of surprises due to inaccurate determination of corneal curvature using these devices and standard measurements. The same situation tends to occur in individuals whose corneas have been subjected to other surgical treatments that affect corneal curvature, such as corneal transplantation, radial keratotomy, deep anterior lamellar keratoplasty, Descemet-stripping automated endothelial keratoplasty, and phototherapeutic keratectomy. In comparison, topography can accurately detect the mean pupillary power rather than just 4 to 6 points in the medium periphery. Topography measures the actual power of the entire pupillary area that is involved with visual acuity.