Corneal stiffening after cross-linking questioned by deformation testing

PARIS — Cross-linked corneas were not found to be stiffer than normal corneas in a study performed with the Corvis ST tonometer.

The Corvis ST (Oculus) uses Scheimpflug technology to visualize and measure the corneal deformation response to an air pulse, providing information on stiffness and viscoelasticity.

“We measured the biomechanical changes produced on the cornea by LASIK, PRK, intracorneal rings (ICRs) and cross-linking 1 month postop. As expected, we found that all the Corvis parameters were modified by the thinning of the cornea in PRK and LASIK and that ICRs had an influence on the pattern of deformation. Surprisingly, no significant change was found from preop in cross-linked corneas, and there was in fact a slight trend towards increased deformability,” David Touboul, MD, said at the meeting of the French Society of Ophthalmology.

David Touboul

Stiffening of the cornea after cross-linking has been proven in animal eyes but not in human eyes.

“The Corvis ST introduces a new dimension, which involves velocimetry and morphology. It is the first and only test that can prove stiffening in a clinical setting,” Touboul said.

It is difficult at this stage to draw conclusions, he said. The positive effects of cross-linking might be due to other reasons than increased stiffness, such as “changes in configurational entropy of the collagen molecules, renewal of the nerves or keratocytes. Some biological process that we do not know yet.” However, further studies are needed before any hypothesis can be reasonably formulated, he said.

Disclosure: Touboul has no relevant financial disclosures.