Cornea microstructure and mechanical responses measured with nonlinear optical and optical coherence microscopy using sub-10-fs pulses

Qiaofeng Wu,Brian E Applegate,Alvin T Yeh

doi:10.1364/boe.2.001135

Abstract

A combined nonlinear optical microscopy (NLOM) and optical coherence microscopy (OCM) imaging system has been assembled in order to simultaneously capture co-registered volumetric images of corneal morphology and biochemistry. Tracking of cell nuclei visible in the OCM volume enabled the calculation of strain depth profile in response to changes in intraocular pressure for rabbit cornea stroma. Results revealed nonlinear responses with a depth dependent strain distribution, exhibiting smaller strains in the anterior and larger strains in the posterior stroma. Cross-sectional images of collagen lamellae, visible in NLOM, showed inhomogeneous collagen structure along the anterior-posterior direction that correlated well with the noted heterogeneous corneal mechanical responses.

Highlights

Mechanical properties of the cornea play a central role to its multifaceted function of serving as both a physical barrier and the primary refractive element in the eye
Cornea biomechanics have been found to affect seemingly routine intraocular pressure (IOP) measurements which appear to correlate with central cornea thickness and curvature, though in a non-straightforward manner as to preclude a simple correction for applanation tonometry [1,2,3,4]
There is accumulating evidence that the stroma is mechanically heterogeneous including ultrastructural measurements that showed more isotropic distribution of collagen lamellae in the anterior third compared with the posterior two-thirds [10], measurements of central cornea collagen microstructural responses to changes in IOP that exhibited differences among the anterior, mid, and posterior regions [11], and swelling experiments that attributed the maintenance of corneal curvature to a comparatively stiff anterior one-third relative to the posterior two-thirds [12]

Summary

Introduction

Mechanical properties of the cornea play a central role to its multifaceted function of serving as both a physical barrier and the primary refractive element in the eye. Our present understanding of its mechanical response and underlying microstructural basis is derived from disparate measurements of tissue biomechanics and ultrastructure performed under different conditions and sample preparations. Tissue mechanical properties are characterized by testing measurements that track the displacement of fiducial markers with applied loads [6,7,8]. There is accumulating evidence that the stroma is mechanically heterogeneous including ultrastructural measurements that showed more isotropic distribution of collagen lamellae in the anterior third compared with the posterior two-thirds [10], measurements of central cornea collagen microstructural responses to changes in IOP that exhibited differences among the anterior, mid, and posterior regions [11], and swelling experiments that attributed the maintenance of corneal curvature to a comparatively stiff anterior one-third relative to the posterior two-thirds [12]

Methods

Results

Conclusion