What is corneal biomechanics and why it is important?

by Ahmed Elsheikh, Professor of Biomaterial Mechanics, University of Liverpool

​The cornea plays an important role in allowing us to form clear images of the world. It is responsible for two thirds of the refractive power of the eye, or its ability to focus light on the retina. This important function is only possible when the cornea maintains a particular curved shape, which depends on a fine equilibrium between the eye’s internal fluid pressure and the cornea’s mechanical resistance or biomechanics. 

With diseases, such as keratoconus, the cornea’s biomechanics deteriorates causing bulging, loss of the tissue’s regular shape and loss of clear vision.

The ability to measure corneal biomechanics is of great clinical importance. There are several processes and surgical procedures that either interact or interfere with corneal biomechanics, and in these cases, knowledge of biomechanics is essential for their customisation for individual patients’ needs.

For example, the ability to characterise the deterioration of corneal biomechanics in keratoconic eyes would enable customisation of a treatment regime called collagen cross-linking that can stiffen the tissue to its natural levels. Another example is in refractive surgeries such as LASIK and SMILE. These surgeries involve removing a tissue layer in order to re-shape the cornea’s front surface. With tissue loss, cornea’s stiffness reduces, allowing it to deform more under the eye’s internal pressure. In these applications, knowledge of corneal biomechanics would allow the accurate prediction of post-surgery corneal shape and hence better selection of surgery parameters.

Other applications include cataract surgeries where a peripheral incision is made in the cornea to enable removing the natural crystalline lens and introduction of the artificial intraocular lens in its place. This incision changes corneal biomechanics leading to changes in its geometry.

The ability to measure corneal biomechanics in vivo has been a major challenge. While we knew from ex vivo laboratory experiments that the biomechanics change with age and diseases (such as keratoconus, diabetes and glaucoma), we have not been able to measure the tissue’s biomechanical properties in vivo. 

Our IMCUSTOMEYE project is intended to address this challenge through the development of medical devices that can estimate corneal stiffness and viscoelasticity (the most important corneal biomechanical properties) in vivo. Initial results indicate the robustness of our new technologies and their suitability for clinical application within a few years of project end. Our studies will go beyond the measurement of corneal stiffness and viscoelasticity to their implementation to customise various clinical processes and procedures.