A new method for individualized characterization of the distribution of collagen fibril dispersion using corneal aberrations

Abstract

Purpose : The spatial distribution of collagen fibril dispersion (CFD) has a significant impact on corneal biomechanical and optical behaviors. We proposed a novel method to characterize the distribution of CFD from IOP-induced changes in corneal optical aberrations.

Methods : Our characterization method was based on a linear correlation found between the IOP-induced changes in corneal wavefront aberrations and the degree of CFD. The method was tested through both theoretical simulations and ex vivo experiments on three rhesus monkey corneas (male, 156 days old (n=2) and 10 years old (n=1)). Inflation tests with multiple levels of IOP (ranging from 5 to 40mmHg) were conducted numerically in corneal models with three arbitrarily assumed patterns of CFD and experimentally on the monkey corneas. Corneal geometry, depth-dependent matrix stiffness and the IOP-induced changes in optical aberrations for a 6mm diameter were measured for individual corneas. An individualized model with customized CFD was developed for each cornea using finite element software (ABAQUS 6.14) and the estimated optical aberrations were compared with the measured data.

Results : For the theoretical investigation, all of the three assumed distributions of CFD were successfully characterized (Fig.1a). The estimated IOP-induced changes in corneal aberrations closely matched the measured data (Fig.1b). The RMS difference between the estimated and the measured corneal aberrations averaged for three IOPs was 0.29, 0.24 and 0.10μm for three assumed fibril dispersion patterns, respectively. Increased estimation errors were observed in ex vivo experiments. The overall features of the IOP-induced changes in corneal aberrations were still estimated for 2 monkey corneas (Fig.1c, 1d). The average RMS difference for these two corneas was 0.57 and 0.43μm. The characterization of CFD for the third cornea might be affected by corneal hydration during the experiment, which resulted in an increased RMS difference, 0.80μm.

Conclusions : A method proposed to characterize the distribution of CFD using changes in corneal aberrations was demonstrated by both theoretical simulations and ex vivo experiments. With this method, a more advanced corneal model with individual spatial distribution of CFD can be developed and used to improve our ability to understand optical and biomechanical behaviors of corneas.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.