Corneal wound healing following excimer laser ablation

The excimer laser is currently being investigated in ophthalmology for refractive correction, including myopia, hyperopia and astigmatism. Laser photo ablation offers a consistent, precisely controllable method of tissue removal that potentially gives the surgeon more accurate control of surgical results than do conventional methods of corneal reshaping (i.e., diamond knives for radial keratotomy). In addition, there is interest in using laser photo ablation to smooth irregular corneal surfaces and to remove corneal stromal opacities. Early clinical studies have elucidated two problems common to refractive surgery. First, the cornea tends to develop a subepithelial haze approximately two weeks post-op in the ablation zone. In most cases this subsides during the ensuing six months. Second, the initial level of refractive correction reverses during the process of healing. This problem tends to be exaggerated in patients whose correction is greater than five diopters requiring a deeper ablation. Depending on the depth of the ablation, the epithelium, Bowman’s layer and the anterior stroma will be removed. The reparative process includes reepithelialization and the restoration of the stroma through the migration of keratocytes to the wound area. This is followed by the secretion of collagenases as well as new collagen and extracellular matrix (GAGs).