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C.J. Roberts, J.L. Güell, A.M. Mahmoud, F. Velasco, M.T. Sisquella; The Influence of Hinge Placement on the Corneal Shape Response to the Creation of a Flap in LASIK . Invest. Ophthalmol. Vis. Sci. 2004;45(13):208.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the influence of hinge placement on corneal shape response to the making of a LASIK flap. Methods: Ten eyes of 10 patients who were scheduled for bilateral laser in situ keratomileusis (LASIK) were prospectively recruited. The Moria M2 130 microkeratome (Microtech, France ) was used to create a superior–nasal hinge in one eye and a superior–temporal hinge in the contralateral eye. The Keratron Scout (Optikon, Rome, Italy) was used to acquire corneal topography before and immediately after the flap was created, prior to ablation. The topographic exams were exported to custom software for analysis. A Zernike decomposition was performed on the topographic elevation data. The surface was iteratively reconstructed, and the curvature map calculated. The optimized reconstructed order was determined (up to 12th), based on a minimization of the fit error in curvature. Results: When analyzed as a group (n=10), the creation of the LASIK flap produced a significant increase in C7, the vertical coma term (p<0.0187). No other higher order terms were affected. A small, but significant (p<0.0251) decrease in the magnitude of the C4 or second order defocus term was also observed, indicative of central flattening or a hyperopic shift. In comparison between hinge position groups (n=5 in each group), only C8, or horizontal coma was different between groups. No other terms showed a significant difference. Tangential topography maps demonstrated a pattern of inferior steepening indicative of oblique coma oriented as a function of hinge position. Conclusions: The creation of either a superior–nasal or a superior–temporal hinged flap with a MORIA M2 130 microkeratome induces vertical coma via topography, and the orientation of the coma on either side of the vertical axis is dependent on whether the hinge is nasal or temporal. This information may be important in planning customized ablations in the future.
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