Effect of penetration enhancer with novel corneal cross-linking using recombinant human decoron in porcine eyes.

The aim of the study was to investigate the effectiveness of exogenous recombinant human decoron and an accompanying penetration-enhancing solution in stiffening ex-vivo porcine corneas both transepithelially and after de-epithelialization. Eight porcine paired eyes were treated transepithelially: one eye with a pre-treatment solution (Pre-Tx), penetration enhancing solution (PE), and decoron while the fellow eye was treated by the same protocol but without decoron. A second group included 4 de-epithelialized pairs treated identically. The final group included 4 de-epithelialized pairs with one eye treated with Pre-Tx, PE, and decoron while the fellow eye was treated without PE. Uniaxial tensile testing was used to compare the corneal stiffness between the different treatment conditions. Residual tissue underwent immunohistochemistry analysis to evaluate the depth of penetration of decoron into the corneal stroma. There was no stiffening effect exhibited among corneas treated transepithelially with decoron compared to control (P > 0.05) and poor stromal penetration was exhibited on tissue analysis. Among de-epithelialized corneas, there was a significant stiffening effect seen in those treated with decoron at 3%, 4%, 5%, & 6% strain (P < 0.05) compared to control. Among de-epithelialized corneas there was also a significant stiffening effect seen in those treated with the PE and decoron at 4%, 5%, & 6% strain (P < 0.05) with improved stromal penetration confirmed by immunohistochemistry, versus without PE. De-epithelialization is necessary for effective stromal penetration of decoron. Depth of penetration and subsequent corneal stiffening may be improved with a penetration enhancing solution. Compared to riboflavin, decoron requires shorter treatment time and spares UV light exposure.

Biomechanical contribution of the sclera to dynamic corneal response in air-puff induced deformation in human donor eyes.

This study was conducted to evaluate the impact of varying scleral material properties on the biomechanical response of the cornea under air-puff induced deformation. Twenty pairs of human donor eyes were obtained for this study. One eye from each pair had its sclera stiffened using 4% glutaraldehyde, while the fellow eye served as control for uniaxial strip testing. The whole globes were mounted in a rigid holder and intraocular pressure (IOP) was set using a saline column. Dynamic corneal response parameters were measured before and after scleral stiffening using the CorVis ST, a dynamic Scheimpflug analyzer. IOP was set to 10, 20, 30, and 40 mmHg, with at least 3 examinations performed at each pressure step. Uniaxial tensile testing data were fit to a neo-Hookean model to estimate the Young's modulus of treated and untreated sclera. Scleral Young's modulus was found to be significantly correlated with several response parameters, including Highest Concavity Deformation Amplitude, Peak Distance, Highest Concavity Radius, and Stiffness Parameter-Highest Concavity (SP-HC). There were significant increases in SP-HC after scleral stiffening at multiple levels of IOP, while no significant difference was observed in the corneal Stiffness Parameter - Applanation 1 (SP-A1) at any level of IOP. Scleral mechanical properties significantly influenced the corneal deformation response to an air-puff. The stiffer the sclera, the greater the constraining effect on corneal deformation resulting in lower displaced amplitude. This may have important clinical implications and suggests that both corneal and scleral material properties contribute to the observed corneal response in air-puff induced deformation.

Biomechanical Impact of the Sclera on Corneal Deformation Response to an Air-Puff: A Finite-Element Study.

Aim or Purpose: To describe the effect of varying scleral stiffness on the biomechanical deformation response of the cornea under air-puff loading via a finite-element (FE) model. Methods: A two-dimensional axisymmetric stationary FE model of the whole human eye was used to examine the effects varying scleral stiffness and intraocular pressure (IOP) on the maximum apical displacement of the cornea. The model was comprised of the cornea, sclera, vitreous, and surrounding air region. The velocity and pressure profiles of an air-puff from a dynamic Scheimpflug analyzer were replicated in the FE model, and the resultant profile was applied to deform the cornea in a multiphysics study (where the air-puff was first simulated before being applied to the corneal surface). IOP was simulated as a uniform pressure on the globe interior. The simulation results were compared to data from ex vivo scleral stiffening experiments with human donor globes. Results: The FE model predicted decreased maximum apical displacement with increased IOP and increased ratio of scleral-to-corneal Young's moduli. These predictions were in good agreement (within one standard deviation) with findings from ex vivo scleral stiffening experiments using human donor eyes. These findings demonstrate the importance of scleral material properties on the biomechanical deformation response of the cornea in air-puff induced deformation. Conclusion: The results of an air-puff induced deformation are often considered to be solely due to IOP and corneal properties. The current study showed that the stiffer the sclera, the greater will be the limitation on corneal deformation, separately from IOP. This may have important clinical implications to interpreting the response of the cornea under air-puff loading in pathologic conditions.