Finite element analysis of astigmatic keratotomy based on corneal biomechanical properties

Objective To establish a finite-element biomechanical model of astigmatic keratotomy, and to investigate the impact of surgical parameters on corneal deformation, stress distribution and astigmatism correction. Methods With Rhinoceros modeling and Abaqus finite element analysis software, a three-dimensional finite-element model of astigmatic cornea was developed, and surgical parameters such as incision optical zone, incision depth and length were varied. Postoperative corneal stress, apical deformation and astigmatism correction were assessed. Results A significant increase of stress was noticed near corneal incisions, and maximum corneal stress decreased with the increase of incision depth. Both anterior and posterior corneal surface moved slightly forward postoperatively. Maximum corneal stress was 340 392, 361 022 and 214 187 Pa, and anterior and posterior apical deformation was 49.80, 51.64, 55.53 μm and 54.15, 55.91, 59.67 μm, with 45°, 60° and 90° in arc length of the incision, respectively. The refractive power decreased in steep meridian and increased in flat meridian, resulting in a total decrease of corneal astigmatism. The magnitude of astigmatism correction was 0.85, 1.59, 2.23 and 3.06 D with 30°, 45°, 60° and 90° in arc length of the incision, respectively. Conclusions The finite-element biomechanical model of astigmatic keratotomy could be used to predict the optical outcomes after surgery. The magnitude of astigmatism correction is positively correlated with the surgical incision arc length. (Chin J Ophthalmol, 2016, 52: 674-680) Key words: Astigmatism; Refractive surgical procedures; Cornea; Biomechanics; Finite element analysis