Tangential topography corneal map to diagnose laser treatment decentration

PURPOSE: To describe the use of corneal topography to determine the cause of decentration and pseudodecentration after laser ablation METHODS: A total of 148 eyes referred for treatment of decentration after primary excimer laser surgery were evaluated using corneal topography. The criteria and maps used to distinguish between decentration and pseudodecentration are described. All eyes were analyzed with the tangential algorithm of the CSO corneal topographer and the NIDEK OPD-Scan. RESULTS: Eyes were classified into two groups: decentered and pseudodecentered. Only 5 (3.4%) eyes were decentered, and 143 eyes were classified as pseudodecentered. Analysis of the different causes of pseudodecentration included 28 cases due to an irregular ablation, 107 cases due to high corneal dioptric gradient, and 8 cases due to central islands. Instantaneous corneal topography was the most suitable map to determine decentration and pseudodecentration. CONCLUSIONS: Decentration and pseudodecentration were due to corneal topographic abnormalities causing sudden changes of corneal curvature in the midperiphery. The evaluation of the instantaneous curvature maps in this study underscores the importance of these peripheral changes by highlighting their impact on the optical performance of the central cornea.