Multiaxial mechanical behavior of the porcine anterior lens capsule

Abstract

The biomechanics of the lens capsule of the eye is important both in physiologic processes such as accommodation and clinical treatments such as cataract surgery. Although the lens capsule experiences multiaxial stresses in vivo, there have been no measurements of its multiaxial properties or possible regional heterogeneities. Rather all prior mechanical data have come from 1-D pressure-volume or uniaxial force-length tests. Here, we report a new experimental approach to study in situ the regional, multiaxial mechanical behavior of the lens capsule. Moreover, we report multiaxial data suggesting that the porcine anterior lens capsule exhibits a typical nonlinear pseudo-elastic behavior over finite strains, that the in situ state is pre-stressed multi-axially, and that the meridional and circumferential directions are principal directions of strain, which is nearly equi-biaxial at the pole but less so towards the equator. Such data are fundamental to much needed constitutive formulations.

Accommodation of the human lens capsule using a finite element model based on nonlinear regionally anisotropic biomembranes

“…Their work has been largely based on uniaxial tests on thin strips cut out from the lens capsule and their data presented in terms of linear elasticity. More recent work from our group revealed, however, that the lens capsule exhibits a nonlinear, regionally anisotropic behavior (Heistand et al 2005;Heistand et al 2006;Pedrigi, Staff et al 2007). These data and findings are used as key assumptions in the present model of human lens accommodation.…”

Redistribution of strain and curvature in the porcine anterior lens capsule following a continuous circular capsulorhexis

“…Our basic test system, experimental procedures, and methods for strain analysis are similar to those reported in Heistand et al (2005). Briefly, we mount fresh, enucleated eyes in a moldable wax fixture, remove the cornea and iris, and then affix numerous closely placed, 40-mm diameter fluorescent microspheres (markers) to the surface of the anterior lens capsule.…”

“…As shown in Heistand et al (2005), the normal lens capsule is under a pre-strain of roughly 12% in both the meridional and circumferential directions. Herein, however, we compute changes in strain from the native values; we do not compute the actual values of strain.…”

“…Global reconstruction techniques can be used with the biplane video system to determine the 3-D position of the centroid of each marker (Heistand et al, 2005). Thereafter, a Delaunay triangularization technique (Matlab) was used to construct an array of lines connecting marker centroids, thus forming a mesh of triangles over the entire field of markers, with nodes at each marker centroid.…”

Inverse elastographic method for analyzing the ocular lens compression test

“…6 Previous methods for estimating lens sti®ness include spinning tests, [7][8][9] dynamic mechanical analysis, 10 indentation, 11,12 penetration, 13 Brillouin microscopy, [14][15][16][17][18][19] acoustic methods, 20,21 and compression. [22][23][24][25][26][27] The lens capsule has been mechanically characterized by in°ation testing 28,29 and uniaxial tensile testing. 30,31 However, no test has yet enabled a simultaneous mechanical analysis of both the lens and its capsule.…”