Abstract
Purpose :
We performed multivariate analyses of anisotropic, hyperelastic biomechanical properties of the human cornea using in vivo air-puff applanation and inverse finite element technique.
Methods :
50 eyes of 25 normal subjects, ranging in age from 11-50 years, were imaged with Corvis-ST and Pentacam (OCULUS Optikgerate Gmbh, Germany). Inclusion criteria were spherical equivalent less than -3D, no prior ocular surgery, no inflammation and no corneal degenerations. Cornea deformation from Corvis-ST and 3-D geometry from Pentacam was used to construct patient-specific inverse finite element models based on a recent study (Sinha Roy et al., J Mech Behav Biomed Mat 2015; 48:173-82). The recent study quantified the properties using a fiber and depth dependent hyperelastic model with 4 material constants (C10, C20, k1 and k2). C10 and C20 quantified the elastic response of the cellular matrix. k1 and k2 quantified the non-linear stiffening effect of the collagen fibers, arranged in a lamellar network with depth-dependent crosslinks. Multivariate analyses of covariance of material constants was performed with age, intraocular pressure (IOP) and central corneal thickness (CCT) as covariates. Association between the eyes of a subject was also studied in the multivariate model. Mean±standard error of the mean is reported here.
Results :
Mean age, IOP and CCT was 22.4±1.26 years, 534.6±3.8 μm and 15.5±0.4 mmHg, respectively. Mean C10, C20, k1 and k2 was 87.41±6.3 kPa, 5.1±0.25 MPa, 35±0.6 kPa and 154.4±23.5, respectively. C10 (p=0.62), C20 (p=0.42) and k1 (p=0.20) were similar for the left and right eye of the same subject. However, k2 of the left eye was significantly higher than the same of the right eye (p=0.01). k2 was also positively correlated with age (p=0.02) indicating a signficant age related stiffening effect in the human cornea. C10 was positively correlated with CCT (p=0.01). The other constants did not correlate with either age, IOP or CCT (p>0.05).
Conclusions :
We studied the in vivo anisotropic properties of the human cornea as a function of IOP, CCT and age for the first time. Increase in k2 with age indicated some age related stiffening effect in the human cornea. CCT may also influence the biomechanical property of the cellular matrix (C10). Further study with a larger sample size and older subjects is needed to confirm the trends.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.