Corneal elasticity and ocular rigidity in normal and keratoconic eyes

Abstract

The elastic properties of a given tissue may be characterized by Youngs Modulus (Y) which relates the stress (force per unit cross sectional area) and the resultant strain (the relative linear deformation). Cornea and sclera react to stress by a biphasic viscoelastic response consisting of a quick immediate deformation followed by a further slow deformation. Thus, it is necessary to distinguish between Y determined from the immediate elastic response (Yi) and Y determined in steady state (Ys). In a normal (n = 29) and a keratoconic group (n = 27) the ocular rigidity (E) was determined as estimate of the Yi of the ocular tunics. Further based on measurements of intraocular pressure, corneal diameter, corneal shape and thickness profile that value of Ys which represents elastic minimum energy content in the actual corneal membrane was estimated in the two groups. E as well as Ys were found to be significantly lower in keratoconic eyes compared with normals and uncorrelated to each other in the two groups.

Changes of extracellular matrix of the cornea in diabetes mellitus

“…The difference in biomechanical properties between eyes with keratoconus and normal eyes has been determined experimentally [6,7]. Cross-sectional clinical studies on the influence of diabetes mellitus on keratoconus corneas in-vivo, however, are rare [1,2].…”

The pathogenesis of keratoconus

“…The corneal tissue in KC is less rigid than normal tissue 26 and an increased axial length suggests a relationship with myopia. 27 The stroma is predominantly formed of water and type I collagen.…”

Noncontact depth-resolved micro-scale optical coherence elastography of the cornea

“…For example, keratoconus is associated with localized reduced rigidity of the cornea, and the information of the corneal stiffness is useful to provide improved diagnosis and monitoring of this pathological status [3,4]. Also, real-time in vivo measurement of the spatial elasticity distribution with microscopic scale in the cornea could lead to adaptive mechanical modeling of the individual corneal structure [5], which is extremely important to prevent overcorrections, under-corrections and ectasia from refractive surgeries, such as LASIK, and to further optimize the laser ablation procedures [6,7].…”