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Abstract #22477 Published in IGR 10-4
Impact and permanence of LASIK-induced structural changes in the cornea on pneumotonometric measurements: Contributions of flap cutting and stromal ablation
Sánchez-Navés J; Furfaro L; Piro O; Balle SJournal of Glaucoma 2008; 17: 611-618
PURPOSE: To determine the factors that lead to changes in intraocular pressure (IOP) measurements after laser-assisted in situ keratomileusis (LASIK) and their long-term stability. PATIENTS AND METHODS: Five hundred twenty-two myopic eyes and 296 hyperopic eyes were enrolled in the study. Pneumotonometry was used to measure IOP once in the preoperative stage and twice in the postoperative stage 1 month after the operation and 1 year later. Ultrasonic pachymetry was used to determine preoperative and intraoperative corneal thicknesses and axial length of the eye, whereas optical pachymetry was used in the preoperative stage and 1 month after surgery. Corneal topography was used to determine the preoperative and postoperative mean curvature of the anterior surface of the cornea over 3- and 5-mm diameter regions. Comparative statistical analysis of the retrospective data series was performed. RESULTS: A highly significant reduction of IOP readings is found after LASIK for both myopic and hyperopic eyes. The reduction is stable 1 year after LASIK. In the case of myopic eyes, the reduction has a highly significant linear correlation with the amount of tissue ablated in the central region of the cornea. CONCLUSIONS: Pneumotonometric IOP readings after LASIK are reduced, without recovering preoperative values even 1 year after surgery, because of flap cutting and tissue removal in the central region of the cornea. The contribution of flap cutting is estimated to be (1.6 ± 0.8) mmHg, whereas ablation contributes an additional (0.029 ± 0.003) mmHg/μm of removed tissue. This effect should be considered when evaluating the accuracy of IOP measurements in LASIK patients who are at risk for developing glaucoma.
Dr. J. Sánchez-Navés, Department of Physics Instituto Balear de Oftalmología, Ctra. La Vileta, Palma de Mallorca, Spain
