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D.M. Grzybowski, N. Rogers, C. Roberts, R. Lembach; Analysis Of Corneal Biomechanics Based Upon Central And Peripheral Corneal Thickness, Topography And Wavefront Aberration In Normal And Post Refractive Surgery Eyes . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4336.
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© ARVO (1962-2015); The Authors (2016-present)
1) To measure and compare changes in topography, pachymetry and wavefront aberrations of normal cornea and post–LASIK cornea in response to induced corneal edema 2) To evaluate the impact of refractive surgery on the biomechanical corneal forces.
Five subjects (ten eyes) underwent induction of corneal edema by wearing nitrogen (N2) goggles for 2 hours. Two subjects had previously undergone LASIK; three had not. Corneal topography (Orbscan II) and wavefront analysis (Zywave) was performed on each eye prior to and after induction of corneal edema. The change in central and peripheral corneal thickness in each eye was evaluated as was the change in axial and tangential corneal curvatures. The change in the Zernike second and fourth order terms was also calculated. These changes were then compared between post–LASIK and normal eyes.
Analysis of corneal thickness change revealed an increase in corneal thickness in all subjects following exposure to N2. The post–lasik group had a larger (p=0.0039) mean increase in corneal thickness in response to the N2. (Mean central change = 44.533 ± 9.478 for post–lasik; Mean central change = 29.343 ± 3.732 for control). The mean increase in corneal thickness was significantly (p<0.0001) larger in the central cornea than the peripheral cornea when both groups were considered together (post–lasik and control). The interaction term was not found to be significant. The anterior tangential curvature change revealed a pattern in the post–lasik group of more peripheral steepening than central steepening following nitrogen exposure and the interaction term between the two groups was significant (p=0.0364). The control group did not show this pattern. The posterior corneal surface underwent a central steepening in the post–lasik group while the control group experienced a flattening of the central posterior curvature. The group effect for this observation was significant (p=0.0212). Zywave analysis did not reveal a significant change in the second order terms or in the fourth order term of spherical aberration.
Corneas that have undergone Lasik surgery demonstrate an exaggerated response to induced edema, manifested by a larger increase in corneal thickness than normal subjects with intact anterior lamellae. The post–lasik cornea also responds differently in terms of peripheral anterior curvature and central posterior curvature to induced edema. These findings indicate that the biomechanical and swelling forces acting within and upon the cornea are altered after LASIK.
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