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W. J. Dupps, Jr., A. Sinha Roy; Differential Curvature Response to Collagen Crosslinking in Keratoconus: A 3-D Finite Element Modeling Study. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4636.
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To simulate the effects of corneal stiffening on corneal curvature in keratoconic eyes and to compare the topographic effects in central and eccentric cones.
Anterior and posterior corneal surface elevations were obtained with rotating Scheimpflug tomography in both eyes of a keratoconus patient. One eye had a central cone and the other had an eccentric cone. A 3-D finite element model of cornea and sclera was constructed to allow for physiologic corneal boundary conditions. A linear form of Zernike polynomials was used to reconstruct the surfaces of the pre-treatment corneal model. The hyperelastic strength of the anterior 200 microns of the cornea was then increased by factors of 2 and 4 to simulate clinically feasible crosslink-mediated stiffening. Pre- and post-treatment anterior surface axial curvatures were calculated and compared.
The FEM model is depicted in Fig. 1. Figs. 2 and 3 illustrate the treatment-induced changes in tangential power with 200% and 400% anterior corneal stiffening. In the case of a central cone, central flattening and peripheral steepening diametrically opposite the zone of flattening were noted. Focal flattening was as high as 3D with 200% stiffening and 6D with 400% stiffening. In an eccentric cone, the region of flattening was more peripheral, with maximum flattening of 2D with 200% stiffening and 2.8D with 400%. The locus of maximal flattening was concentrated within the cone in both cases.
Central and eccentric cones may exhibit different curvature responses to collagen crosslinking. Central cones are more likely to respond by flattening within the pupillary zone, while eccentric cones are less likely to demonstrate post-treatment central steepening.
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