The far ultraviolet energy of the excimer laser is capable of excising or removing human tissue, such as the anterior layers of the cornea. The cornea provides more than 80% of the refractive power of the eye, and small changes in the shape of the anterior corneal surface can produce refractive changes that are sufficient to correct optical errors in the range of those seen in human eyes. Recent studies in non-human primates suggest that it may be possible to create such changes in the shape of the cornea by removing moderate amounts of corneal tissue safely and precisely with the excimer laser; if so, it may be possible to use the excimer laser to correct optical errors in spectacle- and contact lens-intolerant patients who are nearsighted, farsighted, aphakic, or astigmatic and to provide them with nearly perfect, uncorrected vision without the need for optical devices. Contact lens-intolerant infants and children with monocular cataracts could be treated with the laser to provide rapid visual rehabilitation, facilitating amblyopia therapy, which is essential to prevent blindness in such young patients with developing visual systems. The excimer laser may also be useful for the excision of tumors and benign growths, such as pterygia, as well as the sterilization of infectious lesions such as corneal ulcers caused by viruses, bacteria, or fungi. The overall objective of this proposal is to study the safety and efficacy of excimer laser ablation to alter the anterior curvature of the cornea for the correction of refractive errors.
The specific aims are 1) to test, in non-human primate eyes, the results of central corneal sculpting with the excimer laser for the correction of high myopia, hyperopia, high hyperopia (aphakia), and myopic and hyperopic astigmatism, in terms of safety, efficacy, stability, and long-term corneal clarity and smoothness; 2) to determine the short- and long-term structural effects of laser-created lesions on the primate cornea in terms of the time course of regeneration of the basal lamina complex, the types of collagen produced after laser ablation and the long-term structural stability of the anterior stroma, the mechanism of fibroblast aggregation, and the factors regulating thickening of the epithelium; and 3) to examine the possible cytotoxic/mutagenic effects of the 193 nm laser on corneal tissue. The therapeutic potential for this application of laser energy is considerable and the potential benefits to the patient population with optical errors may be enormous, but there is still much work to be done in the testing and refinement of the system.
