Modeling the Optical Performance of the Human Cornea Following Refractive Surgery

Disturbances of the stromal microstructure occurring in refractive surgical procedures may create unexpected and undesired changes to the vision quality of the eye. Examples of common procedures which can profoundly alter the integrity of the stroma include laser ablation techniques such as Laser in situ keratomileusis (LASIK) for treating myopia, hyperopia and astigmatism, scleral incisions for lens extraction in cataract surgery and conducting keratoplasty (CK) for the treatment of hyperopia and presbyopia. The stroma is the primary load-carrying layer of the cornea and in the normal eye it is in a state of tension resulting from the intraocular pressure (IOP). When a surgical procedure disrupts the stromal tissue, the stresses in the tissue will be redistributed inducing what may be called the biomechanical response of the tissue to the surgical procedure. In the case of LASIK and CK, for example, surgeons wish to change the optical power of the cornea by reshaping the anterior surface. Biomechanically induced deformations may cause the achieved power to deviate from the planned correction and may also introduce aberrations in the resulting optical path. In contrast, in cataract surgery, surgeons may wish to preserve the original power of the cornea and in this case biomechanical deformations may defeat this objective.