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B. Audrey Nguyen, Cynthia J Roberts, Matthew Aaron Reilly; Preliminary study on biomechanical contribution of the sclera to dynamic corneal response in air-puff induced deformation. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1410.
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It has been shown experimentally that the biomechanical deformation response of the cornea to an air-puff may be impacted by its boundary conditions. We present a preliminary study showing the effect of varying scleral properties on corneal biomechanical response to air-puff induced deformation.
Human donor eyes (8 pairs) were obtained for this study. One eye from each pair had its sclera stiffened using 1% or 4% glutaraldehyde, while the fellow eye served as control for follow up uniaxial strip testing. Dynamic corneal response (DCR) parameters were measured before and after scleral stiffening using the Corvis ST at IOPs of 10, 20, 30, and 40 mmHg. Uniaxial tensile strip testing data were fit to a Neo-Hookean model to estimate stiffness ratios of treated sclera to untreated cornea and untreated sclera to untreated cornea. Paired t-tests compared the change in DCRs following treatment (delta), and MANCOVA analyses were performed for selected delta DCRs as dependent variables with IOP and estimated scleral stiffness as independent co-variates. An axisymmetric, steady-state, hyperelastic finite-element (FE) model of the human eye, comprised of cornea, sclera, and vitreous humor was constructed from literature values to simulate Corvis ST loading on the eye.
Mean treated and untreated sclera-to-cornea stiffness ratios were 6.7 and 2.6, respectively. Paired t-tests showed statistically significant (p < 0.05) decreases in the following DCRs at highest concavity (HC) and low IOP (10 mmHg) after scleral stiffening: maximum deformation amplitude (DAmax), peak distance, and DA Ratio Max 2mm and 1mm. MANCOVA results showed significant relationships with both IOP and stiffness for all parameters listed and significant interaction between IOP and stiffness for DAmax. Decreasing values in HC DCRs at IOP of 10 mmHg were predicted in the FE model.
We present a preliminary study that examines the impact of sclera stiffening on corneal biomechanical response to an air-puff. The experimental results demonstrate that stiffened sclera limits corneal deformation at lower IOP, and the simulation results of the FE model also predict these findings. This has important clinical implications, and suggests that the observed corneal biomechanical response in air-puff induced deformation has contributions from both corneal and scleral material properties.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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