Posters

Characterization of the corneal mechanical behavior along the time after treatment with corneal collagen cross-linking

Poster Details

First Author: Á.Ortillés Gonzalo SPAIN

Co Author(s):    J. Rodriguez Matas   J. Cristobal Bescos   B. Calvo Calzada              

Abstract Details

Purpose:

Most of the mechanical tests described to determine the corneal biomechanical properties after corneal collagen crosslinking (CXL) are performed in in vitro animal models. Corvis ST is the only device that provides the in vivo mechanical corneal response, but it has been described that the corneal deformation response to an air puff is dependent on intraocular pressure (IOP) and corneal thickness (CT) and not only of the corneal biomechanical properties. A new in vivo indentation test is validated in an experimental animal model to assess the corneal mechanical behavior after CXL along the time, considering the IOP and CT effect.

Setting:

Department of Ophthalmology, Lozano Blesa University Clinic Hospital (Zaragoza, Spain); Aragón Institute of Engineering Research (i3A), University of Zaragoza (Zaragoza, Spain); LaBS, Department of Chemistry, Materials and Chemical Engineering Giulio Natta, Politecnico di Milano Italy.

Methods:

CXL (3 mW/cm2; 370 nm) for 20 minutes was performed in both eyes of twelve male New Zealand white rabbits (2-2.5 kg) under intramuscular and topical anaesthesia after the removal of the corneal epithelium. In vivo indentation tests were performed twice in each eye (corneal centre) before (PreCXL; n=24) and after CXL at 7th day (PostCXL-7d; n=16), 21th day (PostCXL-21d; n=8) and 56th day (PostCXL-56d; n=8). IOP/CT were measured before each test. Furthermore, in vitro uniaxial tensile tests and corneal immunohistochemistry were performed after the euthanasia of four rabbits in PreCXL (n=8), PostCXL-7d (n=8) and PostCXL-56d (n=8).

Results:

In vivo indentation tests: there were no statistically significant differences between all groups. However, in average, the PostCXL-7d cornea showed the most compliant behavior, and thereafter was observed a progressive recovery of corneal stiffness until PostCXL-56d. In vitro uniaxial tensile tests: there were statistically significant differences between the tangent modulus of PreCXL/PostCXL-7d and PreCXL/PostCXL-56d. The corneal tissue showed the stiffest behavior in PostCXL-7d remaining practically constant until PostCXL-56d. Immunohistochemistry: in PostCXL-7d was observed a cell lack in the anterior stroma and the number of positive (mitotic) cells was significantly greater. PostCXL-56d showed a normal stromal cell density again.

Conclusions:

The in vivo indentation test did not show to be a statistically significant discriminant to assess the mechanical effects of the CXL and the corneal structural recovery in the same patient along the time. However, it is hypothesized that in the case of pathologic eyes (progressive keratoconus or infectious keratitis) where the collagen structure is severely compromised, significant differences could be found. The effect of CXL on the corneal collagen structure can be reliably observed using uniaxial tests.

Financial Disclosure:

NONE