THE DISTRIBUTION OF STRAIN IN THE HUMAN CORNEA

Experimental data on the mechanics of human cornea is meager and somet imes flawed. Moreover, questions regarding the correct material symmet ry and the role of the fibrous microstructure are usually glossed over when mechanical models of the cornea and corneal shape changing proce dures are presented. Accordingly, the deformation of 14 intact human c orneas was measured for five pressures in the physiologic range (0, 5, 10, 25 and 45 cmH(2)O) by tracking small, self-adherent particles pla ced on their anterior surfaces. The meridional strains: calculated in five regions assuming axisymmetric deformation, are small, the average strain in the apical region being 1.14% at 45 cmH(2)O. Results also i ndicate that the strain distribution is unexpectedly nonuniform with s tatistically significant (p < 0.01, typical) variations between region s and a minimum occurring approximately half-way between apex and limb us. To better understand these results, a finite-element moder (FEM) o f the cornea was constructed and used to simulate the experiment. The heterogeneous model shows that our data may reflect the changing fiber orientation along a meridian suggested in the literature. The implica tions of a link between microstructure and mechanics are discussed in light of clinical procedures, such as radial keratotomy, the outcomes of which are dependent on corneal mechanical properties. (C) 1997 Else vier Science Ltd.