Henry Gelender1. 1. Cornea Associates of Texas, Dallas, Texas, USA.
Abstract
PURPOSE: This study tests the hypothesis that the keratometric value derived from Orbscan II mean power maps, when used in an intraocular lens (IOL) calculation formula, at a specific measurement zone, will accurately determine the power of an IOL for planned cataract surgery in patients who have undergone prior myopic laser-assisted in situ keratomileusis (LASIK). METHODS: This is a two-part study conducted in a referral practice. Experiment 1 is a prospective study of 59 eyes of 30 patients undergoing LASIK. The change in Orbscan mean power maps at five central zones (1.0, 1.5, 2.0, 2.5, and 3.0 mm) was compared with the refractive change from LASIK to determine the optimum Orbscan correlation zone. In Experiment 2, the power of the LASIK-altered cornea was measured by Orbscan and applied to IOL calculations for 17 eyes of 13 patients undergoing cataract surgery. RESULTS: In Experiment 1, analysis at the Orbscan 1.0-mm measurement zone demonstrated overestimation of the refractive change, whereas the 2.5-mm and 3.0-mm zones demonstrated underestimation. The 1.5-mm and 2.0-mm zones best approximated the net refractive change following LASIK. In Experiment 2, the Orbscan power at 1.5 mm was selected for IOL calculations to minimize undercorrections. The refractive error following cataract surgery ranged from -0.75 to +0.90 diopters (average, +0.05 diopters). Eight eyes were overcorrected (average, -0.52 diopters) and nine eyes were undercorrected (average, +0.54 diopters). CONCLUSIONS: The 1.5-mm Orbscan II zone measures the effective power of the LASIK-altered cornea. When applied to an IOL calculation formula, it accurately predicts the IOL power for planned cataract surgery.
PURPOSE: This study tests the hypothesis that the keratometric value derived from Orbscan II mean power maps, when used in an intraocular lens (IOL) calculation formula, at a specific measurement zone, will accurately determine the power of an IOL for planned cataract surgery in patients who have undergone prior myopic laser-assisted in situ keratomileusis (LASIK). METHODS: This is a two-part study conducted in a referral practice. Experiment 1 is a prospective study of 59 eyes of 30 patients undergoing LASIK. The change in Orbscan mean power maps at five central zones (1.0, 1.5, 2.0, 2.5, and 3.0 mm) was compared with the refractive change from LASIK to determine the optimum Orbscan correlation zone. In Experiment 2, the power of the LASIK-altered cornea was measured by Orbscan and applied to IOL calculations for 17 eyes of 13 patients undergoing cataract surgery. RESULTS: In Experiment 1, analysis at the Orbscan 1.0-mm measurement zone demonstrated overestimation of the refractive change, whereas the 2.5-mm and 3.0-mm zones demonstrated underestimation. The 1.5-mm and 2.0-mm zones best approximated the net refractive change following LASIK. In Experiment 2, the Orbscan power at 1.5 mm was selected for IOL calculations to minimize undercorrections. The refractive error following cataract surgery ranged from -0.75 to +0.90 diopters (average, +0.05 diopters). Eight eyes were overcorrected (average, -0.52 diopters) and nine eyes were undercorrected (average, +0.54 diopters). CONCLUSIONS: The 1.5-mm Orbscan II zone measures the effective power of the LASIK-altered cornea. When applied to an IOL calculation formula, it accurately predicts the IOL power for planned cataract surgery.
Authors: Sergio Sónego-Krone; Gerson López-Moreno; Oscar V Beaujon-Balbi; Carlos G Arce; Paulo Schor; Mauro Campos Journal: Arch Ophthalmol Date: 2004-02
Authors: H John Shammas; Maya C Shammas; Antoine Garabet; Jenny H Kim; Abraham Shammas; Laurie LaBree Journal: Am J Ophthalmol Date: 2003-09 Impact factor: 5.258