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Benjamin D. Abramowitz, Ashraf M. Mahmoud, Cynthia J. Roberts, Amit Tandon, Deborah M. Grzybowski; Swelling Analysis Of Thickness, Curvature, And Biomechanical Properties In The Post-LASIK Cornea. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5186.
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To investigate potential differences in swelling patterns and biomechanical changes with increased hydration between non-surgical and post-LASIK eyes due to the structural alterations induced by LASIK.
20 non-surgical (mean 34.5±12 yrs.) and 20 post-LASIK (mean 39.9±12.5 yrs.) subjects were recruited. Subjects wore air tight goggles for two hours while a constant flow of humidified nitrogen induced swelling to mimic physiologic conditions of increased corneal hydration. Participants were scanned before and immediately after the swelling period and variables were analyzed using univariate analysis of variance. The Orbscan II provided central, paracentral, and peripheral pachymetry measurements and axial curvature (AC). Scans from the Optovue RTVue measured central pachymetry. Data from the Reichert Optical Response Analyzer (ORA) included Goldmann-correlated IOP (IOPg), corneal compensated IOP (IOPcc), corneal resistance factor (CRF), corneal hysteresis (CH), and peak 1 from analysis of the infrared signal.
All regions increased significantly in pachymetry between the pre-swelling and post-swelling periods for both groups (p<0.05). The Orbscan II reported no difference in central swelling between non-surgical (N) and post-LASIK (L) populations, with both groups swelling 8.1% centrally. The RTVue demonstrated significant differences in central pachymetry change between groups (p = 0.001, N: 5.25±1.40%, L: 7.06±1.62%). The groups were significantly different (p<0.05) for central anterior (N: -0.29±0.68D, L: 0.19±0.49D) and posterior (N: -0.026±0.12D, L: -0.17±0.28D) axial curvature change as well. The ORA revealed that the post-LASIK corneas had a significant reduction in CH, a viscoelastic parameter, from 8.90±1.64 to 8.52±1.46 (p = 0.038) while the non-surgical corneas had a substantial reduction in peak 1, a stiffness parameter, from 775.3±100.1 to 687.9±151.8 (p = 0.015). IOPg, IOPcc, and CRF were not significantly different between groups or within groups in response to swelling.
Post-LASIK corneas exhibit distinct thickness, viscoelastic, and curvature pattern changes when compared to non-surgical corneas in response to induced swelling. Other biomechanical properties are unaffected by increased hydration in both groups. These results may have an impact as subjects age and may require ocular interventions and/or medications that impact corneal hydration status.
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