OCT corneal elastography by pressure-induced optical feature flow

Abstract

The viscoelastic properties of the cornea are important determinants of the corneal response to surgery and disease. The purpose of this work is to develop an OCT-based technique for non-contact, high-resolution pan-corneal strain mapping using clinically-achievable pressure changes as a stressor. Porcine corneas were excised and mounted on an artificial anterior chamber that facilitated maintenance of a simulated intraocular pressure (IOP). Pressure was controlled and monitored continuously by saline infusion with an in-line transducer and digital monitor. Mounted specimens were positioned under a laboratory-based high-speed OCT system and imaged in three dimensions at various IOP levels. Matlab and C++ routines were written to perform 2-D bitmap cross-correlation analyses on corresponding images at different pressure levels. Resulting correlations produced a likelihood estimate of the 2-D vector displacement of corneal optical features. Strain maps from cross-correlation analyses revealed local areas of highly consistent displacements interspersed with inter-regional variability. Displacements occurred predominantly along axial vectors. Our analysis produces results consistent with expected and observed displacement of the cornea with varying IOP. Cross-correlation analysis of optical feature flow in the corneal stroma can provide high-resolution strain maps capable of distinguishing spatial heterogeneity in the corneal response to pressure change. A non-destructive, non-contact technique for corneal strain mapping offers numerous potential advantages over tensile testing of excised tissue strips for inferring viscoelastic behavior, and the membrane inflation model employed here could potentially be extended to clinical biomechanical characterizations.