Biomechanical Modeling of Pterygium Radiation Surgery: A Retrospective Case Study

Abstract

Pterygium is a vascularized, invasive transformation on the anterior corneal surface that can be treated by Strontium-/Yttrium90 beta irradiation. Finite element modeling was used to analyze the biomechanical effects governing the treatment, and to help understand clinically observed changes in corneal astigmatism. Results suggested that irradiation-induced pulling forces on the anterior corneal surface can cause astigmatism, as well as central corneal flattening. Finite element modeling of corneal biomechanics closely predicted the postoperative corneal surface (astigmatism error −0.01D; central curvature error −0.16D), and can help in understanding beta irradiation treatment. Numerical simulations have the potential to preoperatively predict corneal shape and function changes, and help to improve corneal treatments.

A simple cornea deformation model

“…In contrast to microscopic models of the cornea like FEM [13][14][15][16][17][18][19], our model of deformation behavior of the cornea is focused on a rather macroscopic description consisting of rigid and elastic transformations. Nevertheless, we were able to find a simpler mathematical model that could describe the observed undercorrection as discussed in [6,[10][11][12].…”

“…We will especially focus on transformations like the docking of the eye to the PI but also the closing of the lenticule. Rather complex mathematical/ computational models are, e.g., elaborated in [13][14][15][16][17][18][19], which make use of FEM methods that can respect some microscopic fiber/anisotropic structure of the corneal tissue. Furthermore, a whole issue was dedicated to 'Corneal Biomechanics' [20].…”

Changes of Corneal Biomechanical Properties upon Exclusive Ytt-/Sr-90 Irradiation of Pterygium

“…Unfortunately, pterygia treated by exclusive Strontium-/Yttrium-90 beta irradiation can induce a further increase in astigmatism, which again correlates positively with their horizontal length (HL) prior to irradiation, probably due to pulling forces of the regressing pterygium [ 22 , 28 ]. The observations of this study support this theory, as both increasing horizontal astigmatism as well as decreasing horizontal length of pterygium size could be shown.…”

“…As mentioned before, pterygia induce astigmatism and other ocular aberrations to a degree that correlates with pterygium size [ 25 , 26 , 27 ]. Pajic et al noted a further increase in astigmatism after exclusive irradiation and attributed this to pulling forces by the retracting pterygium [ 28 ]. Because of this and the potential induction of other corneal aberrations, a secondary excision can become necessary to improve visual quality.…”