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Kristen Ann Mendoza, Cynthia J Roberts, Ashraf M Mahmoud, Riccardo Vinciguerra, Paolo Vinciguerra, Renato Ambrósio, Rebecca Kuennen, David Castellano; Comparison of biomechanical deformation response after myopic LASIK to thin normal corneas.. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4318.
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© ARVO (1962-2015); The Authors (2016-present)
To test the hypothesis that post-LASIK corneas are more biomechanically compliant than normal corneas with similar intraocular pressure (IOP), central pachymetry, and age.
Twenty-seven eyes of 15 subjects who had previously undergone LASIK surgery for myopia or myopic astigmatism were prospectively recruited for biomechanical analysis using the Corvis ST. Subjects were matched to a retrospective dataset of normal subjects (NL) using biomechanically corrected intraocular pressure (bIOP), pachymetry, and age. Corvis dynamic corneal response parameters (DCR’s) compared included: stiffness parameters (SP-A1 and SP-HC) at first applanation (A1) and highest concavity (HC) respectively, A1 Velocity (A1Vel), A1 Deformation Amplitude (DA), DA Max, DA Ratio 2mm, Radius HC (concave radius of curvature), Inverse Radius Sum (InversRad), pachymetry profile (ARTh), and central curvature (SimK3mm). Significance threshold for T-test comparison was .005 using a Bonferroni correction, and statistical analysis was performed using SAS. Additionally, regression analyses were performed of the DCR’s against ARTh and SimK3mm.
Average surgical treatment was -3.76D sphere (±1.12) and -0.76D cylinder (±0.65). The post-LASIK corneas had a significantly lower pachymetry profile and central curvature than NL corneas. Radius HC, InversRad, and DA Ratio 2mm were significantly different between groups, consistent with greater compliance in post-LASIK corneas. SP-HC and DA Max values were not different. Unexpectedly, SP-A1 was significantly higher and A1Vel significantly lower in post-LASIK corneas, implying lower compliance compared to NL corneas. Regression analyses showed significant relationships between ARTh and both SP-A1 and A1Vel (Figures 1a and 1b respectively), as well as SimK3mm and both SP-A1 and A1Vel (Figures 2a and 2b respectively), when the datasets were combined. Regressions were not significant within each group.
Radius HC, InversRad, and DA Ratio 2mm confirmed the hypothesis of lower compliance after myopic LASIK compared to thin normal corneas. However, SP-A1 and A1Vel had values more consistent with increased stiffness. This can be explained by the important effect of the peripheral cornea on the biomechanical response of post-LASIK corneas.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
ARTh Regression Graph
SimK3mm Regression Graph
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