Tissue biomechanics


Human eye has complex biomechanical structure with muscles and tissue structures designed to achieve precise movement and focus to track objects, maintain and regulate pressure inside the eye ball against the environment, etc. The front surface of the eye called cornea loses it's stiffness due to disease or degeneration, thereby reducing the ability to view objects clearly. Biomechanics arm of IBMS uses sophisticated tools to study the role of biomechanics in human visual machinery.

Analytical model based biomechanics of keratoconus

Keratoconus is a progressive eye disease in which corneal collagen thins out causing the cornea to bulge into a cone-like shape. Change in shape of the cornea causes deflection of light which in-turn results in blurred vision. Since collagen gives strength to the cornea, its degradation causes a change in corneal tissue strength. In this study, we analyzed strength of the cornea to evaluate progression of the disease. For achieving this, we assumed that the cornea is made of same material throughout. Then by applying a known amount of force and measuring the deformation of cornea with respect to that force, we calculated material property. This material property was decreased not only in the diseased but also in suspect pool. Hence, this material property could be the key in identifying keratoconic eyes as well as the suspect eyes.

Reference: Mathew F, Natasha P, Rushad S, Roshan G, Himanshu M, Rohit S, Everette J. Remington Nelson, Sinha Roy A. Waveform analyses of deformation amplitude and corneal deformation in normal, suspect and keratoconus eyes.  Journal of cataract and refractive surgery, under review

Top row images show cross-sectional view of a normal and keratoconic eye. The bottom row shows the biomechanical model and result obtained along with the corneal deformation schematic.

Inverse finite element method based corneal biomechanics

Biomechanics of the eye has gained more significance with the advancement of refractive surgery. We developed and evaluated an inverse finite element method to estimate corneal biomechanics. The inverse finite element model is specific to the patient's corneal structure and uses known microscopic tissue construction to achieve higher degree of accuracy. This model, unlike the analytical model does not assume that cornea is made of same material throughout. Hence the model can capture localized problems such as keratoconus better. This is the first collagen fiber dependent corneal biomechanical assessment. 

Reference: Sinha Roy A, Kurian M, Matalia H, Shetty R. Air-puff associated quantification of non-linear biomechanical properties of the human cornea in vivo. Journal of Mechanical Behavior of Biomedical Materials. 2015; 48: 173-82

Schematic describe the process, in which the structure of cornea and its deformation towards known force is used to estimate the corneal biomechanics.