Biomechanical properties of the keratoconic cornea: a review

Abstract

There has been a recent surge of interest in assessing corneal biomechanical properties due to potential clinical applications, particularly in the early detection of keratoconus (KC). This review discusses the effects of keratoconus on the biomechanical properties of the cornea and the current techniques used to detect these changes both in the laboratory and clinical setting. Specific structural changes occurring in the corneal stroma as part of the disease process can be linked to alterations in the viscous and elastic properties of the cornea in keratoconus. Although there are extensive ex vivo studies using techniques such as extensometry and inflation testing to analyse the biomechanical properties of the normal cornea, few have investigated the keratoconic cornea using the same methods. There are a number of ex vivo studies that confirm the effectiveness of collagen cross‐linking in increasing Young's modulus in healthy corneas. Recently, research has focussed on measuring corneal biomechanical parameters in vivo using two commercially available instruments: the Ocular Response Analyser (ORA) and the CorVis ST (CST). Both instruments analyse the dynamic behaviour of the cornea, when temporarily deformed by an air puff; however, the outputs of these instruments are not directly comparable due to differences in the characteristics of the air puff and output parameters. Studies using these instruments have reported significant differences between keratoconic and healthy corneas; however, neither instrument can currently be used in isolation to reliably diagnose keratoconus. Further research analysing the outputs of these instruments may enhance their diagnostic capabilities.

The natural history of corneal topographic progression of keratoconus after age 30 years in non-contact lens wearers

“…The pathogenesis, mechanisms and rate of progression of keratoconus are not completely understood 11. It has been noted that there is an increase in the amount of non-enzymatic cross-linking with increasing age12 likely due to exposure to ultraviolet radiation throughout life, which is a possible mechanism by which keratoconus progression is slowed or halted with increasing age 13.…”

Quantitative Analysis of Corneal Energy Dissipation and Corneal and Orbital Deformation in Response to an Air-Pulse in Healthy Eyes

“…25 Any comparisons made between these machines must adjust for these differences before drawing conclusions.…”

“…16 The behavior hails from the viscous component dissipating energy within the viscoelastic system. 25 Analysis of corneal hysteresis could reveal the viscous damping effect in the complex viscoelastic cornea. 24 The area between the loading and unloading curves for a deformation response to an air-pulse has been previously described by Ishii et al 17 as ''elastic hysteresis.''…”

The importance of corneal biomechanics in assessing first degree family members of keratoconus patients

“…The difference between P1 and P2 is an indicator of the corneal viscosity and is called hysteresis (CH). As for the other parameter, the corneal resistance factor (CRF) highlights the overall resistance and is referred to as the indicator of corneal elasticity [ 24 - 26 ]. In the last years, ORA has been used in the attempt of early detection of subclinical keratoconus and for monitoring its progression.…”