Corneal model may help improve LASIK outcomes

A computer model of the cornea has been helpful in examining the effects of laser ablation on spherical aberration, according to researchers at the University of Rochester. Data gleaned from this eye model can be incorporated into ablation algorithms to decrease the induction of spherical aberration in LASIK, the researchers said.

Geunyoung Yoon, PhD, and colleagues modeled the preoperative cornea as a rotationally symmetric surface. A ray-tracing program and Zernike polynomial fitting were used to calculate the induced amount of spherical aberration after laser ablation. A biological eye model of the corneal surface change after laser refractive surgery was also developed to explain the induced spherical aberrations after myopic and hyperopic treatments.

Clinical data has showed that positive spherical aberration is induced after LASIK for myopia and negative spherical aberration is induced after LASIK for hyperopia. But the researchers’ theoretical calculations with the eye model suggested that the opposite should be the case. When they adjusted the model to account for the laser spot striking the cornea at variable angles of incidence, however, “the theoretically predicted induction of spherical aberration tends to fit better with the myopic and hyperopic clinical data,” the researchers said in the January issue of the Journal of Cataract & Refractive Surgery.

In the biological eye model, the magnitude of the biological response in myopic correction was three times smaller than in hyperopic correction, the researchers said

Spherical aberration is a better predictor than corneal asphericity when estimating the optical quality of the postop cornea, the researchers said. They advocated further investigations and a better understanding of corneal wound-healing responses.