Purchase this article with an account.
IBRAHIM SEVEN, Abhijit Sinha Roy, William Dupps; Finite Element Analysis of Treatment of Corneal Astigmatism with Collagen Crosslinking. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1620.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To test the hypothesis that selective collagen crosslinking can alter corneal astigmatism and to assess the effects of treatment orientation and pattern.
3D geometry of a patient with corneal astigmatism was measured by a Scheimpflug tomography system (Pentacam v.1.61). Elevation data was fit and extrapolated with 12th order Zernike polynomials routine which was coded in Python2.7. The extrapolated data was imported into Solidworks (ver. 2011). The geometry was meshed with hexahedral elements by Trugrid (v. 2.3.3). Corneal biomechanical properties were defined as nonlinear, isotropic and incompressible. The intra-ocular pressure was assumed as 15 mmHg. Finite element analyses were performed using Abaqus (v. 6.11). Since the in vivo (or pre-operation) geometry was pre-stressed by intra-ocular pressure, the geometry was solved for the no-load condition and pre-stresses were calculated. We simulated 4 different crosslinking treatment patterns with a stiffening factor of 2 and effective depth of 300 um. The treatment was simulated with a bow-tie pattern oriented on the steep astigmatism axis (pattern1), a bow-tie pattern oriented on the flat astigmatism axis (pattern2), a fan pattern (pattern3), and a central ellipse pattern oriented on the flat astigmatism axis (pattern4). The corneal anterior surface coordinates were extracted at the end of the each simulation and the anterior surface axial curvature was calculated. The refractive index was as assumed as 1.3375.
Keratometry (Sim K) values in the preoperative eye (in vivo) were 44.85/46.22@78. The SimK value changed to 44.06/46.62@90, 44.83/45.88@45, 44.76/46.27@84, 44.64/45.64@51 with pattern1, pattern2, pattern3, and pattern4 treatment, respectively. The astigmatism value was 1.37in the pre-operation stage. The value changed to 2.56, 1.05, 1.51, and 1.00 with pattern1, pattern2, pattern3, and pattern4 treatment, respectively.
In this pilot study, simulated patterned collagen crosslinking had an effect on corneal astigmatism. Treatments on the steep axis increased astigmatism, while treatments orthogonal to the steep axis decreased astigmatism. Additional clinical geometries with regular and irregular astigmatism will be investigated and modeling will be expanded to include an anisotropic, fiber-dependent hyperelastic material formulation.
This PDF is available to Subscribers Only