Finite-element modeling of posterior lamellar keratoplasty: Construction of theoretical nomograms for induced refractive errors

Purpose: To estimate the theoretical corneal refractive error induced by mechanical weakening effects from posterior lamellar keratoplasty (PLKP) in the human cornea. Methods: The refractive effects of PLKP are simulated by finite-element modeling (FEM) as a mathematical function of the thickness of the excised posterior lamellar corneal button, with a nonlinear formulation of stress-strain relation for the corneal material. A theoretical nomogram was developed to correlate the refractive changes to button thickness. Results: The predicted refractive change after PLKP is less than 1 dpt for a 170-μm thickness posterior corneal button over a broad range of Young's modulus. Thicker buttons result in greater surgically induced refractive errors. Conclusions: According to FEM analysis, the excision of a posterior lamellar button of less than 170 μm thickness produces a minimal predicted refractive change (<1 dpt) in the cornea after PLKP.