Purpose: To quantify the changes in the elevation topography of the front and back corneal surfaces after three different refractive treatments for correcting myopia with standard and custom laser in situ keratomileusis (LASIK) and orthokeratology using corneal refractive therapy.
Methods: We evaluated 20 eyes undergoing orthokeratology for correction of myopia spherical equivalent (mean±SD=−3.41±0.76 D), 18 eyes undergoing custom LASIK surgery (mean±SD=−4.14±0.89 D), and 23 eyes undergoing standard LASIK (mean±SD=−3.61±0.67 D). The values of front and back corneal surfaces were derived by using Pentacam (Oculus, Inc. GmbH, Wetzlar, Germany) before and at least 3 months after each treatment, in the center of the cornea and 4 points to each side of the horizontal meridian at intervals of 1 mm.
Results: Corneal elevation data before treatment were not statistically different between patients in either group (P>0.070, for back and front elevation). After treatment, both surgical procedures significantly increased the positive value of the front elevation beyond an area of 6 mm. The opposite trend was found within the central 5 mm of the cornea, presenting a statistically significant decrease in elevation (P<0.001). In the case of orthokeratology, the elevation experienced a minor but a statistically significant reduction in the central region (P<0.001). On the back surface, the elevation did not undergo statistically significant alterations in any of the procedures and none of the items discussed (P>0.285).
Conclusions: Differences in front corneal elevation changes between LASIK and orthokeratology reveal a much different mechanism for producing corneal power subtraction. The back corneal surface does not suffer significant changes after surgical and nonsurgical treatments for the correction of myopia.
From the Clinical and Experimental Optometry Research Laboratory—CEORLab (A.Q., J.J., J.M.G.-M.), Madrid, Spain; Center of Physics (Optometry), School of Sciences, University of Minho, Braga, Portugal; Department of Optica and Optometria (C.V.-C.), European University de Madrid, Spain; Department of Ophthalmology (A.R.G.), University of Murcia, Murcia, Spain; Department of Mathematics (M.S.R.-Q.), School Gonçalo Sampaio, Póvoa de Lanhoso, Portugal; and Óptica Queirós, Department of Optometry (S.C.P.-M.), Póvoa de Lanhoso, Portugal.
Supported by a grant from the Science and Technology Foundation (FCT) of the Ministry of Science and Superior Education (MCES) (European Social Funding). Doctoral Fellowship (AQ) number SFRH/BD/61768/2009.
The authors have no funding or conflicts of interest to disclose.
Address correspondence and reprint requests to António Queirós, Ph.D., Department of Physics (Optometry), Campus de Gualtar, University of Minho, 4710-057 Braga, Portugal; e-mail: firstname.lastname@example.org
Accepted August 15, 2011.