The Geometric Effect of Arcuate Relaxing Incisions for The Treatment of Corneal Astigmatism

Corneal astigmatism is a refractive error caused by distortion of the normal shape of the cornea. Most corneal astigmatism is regular, i.e., it can be corrected using a sphero-cylindrical lens. When the refractive error of regular astigmatism is too high to be corrected by glasses or contact lenses, arcuate relaxing incisions can be made. The incisions are performed on the cornea`s steepest meridian, and flatten it, causing the cornea to become less cylindrical and more spherical. The incision also causes the meridian perpendicular to it to steepen.

Currently most incisions are done by hand, using decades-old nomograms which specify the number, depth and length of the requires incisions, for different degrees of corneal astigmatism. Incisions can also be made using femtosecond laser.

The aim of this study is to develop a method to calculate the optimal geometrical parameters of relaxing corneal incisions for regular astigmatism.

Based on previously-published biomechanical models of the cornea, We have formulated a numerical model of the cornea. Several simulations were performed using the Finite Element Method (FEM) and the obtained results were compared to the existing literature. Our model showed increased flattening effect with increased depth and length of the incisions, and with decreased distance of the incisions from the center of the cornea. These results were compatible with previous clinical literature.

In the future we will use the built model for the study of non-arcuate incisions as a treatment for irregular astigmatism unamenable to arcuate incisions.