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Up Front | Sep 2007

The Advent of Excimer Refractive Surgery

Ophthalmology has made remarkable achievements in vision correction.

Twenty years have passed since I first aimed an excimer laser at a cornea. I performed the experiment to test the ability of the excimer laser to ablate the cornea. At the time, the Nd:YAG laser stimulated ophthalmologists' interest in laser surgical technologies beyond the photocoagulator, and practitioners sought a laser that would reshape the cornea. I believed that we had found one. The smoothness of the corneal surface and the absence of visible damage to the underlying stroma astounded everyone who saw this particular case. My colleagues and I also noted that four or five excimer laser pulses were necessary to remove 1 µm of tissue. The removal of tissue layers that were thinner than the wavelength of light was strong evidence that this may be a potent technology for producing a controlled modification of the eyes' optical properties. The decade that followed confirmed this idea.

The success of the instruments with which we are familiar today reflects the efforts of many clinical investigators as well as less visible hardware and software engineers. Their labors were driven by the widely recognized limitations of the existing technology for the correction of refractive errors. The ametropic patient was frustrated by the limitations of spectacles and contact lenses, and the ophthalmic surgeon was inhibited by the complication rates, unpredictability, instability, and optical imperfections of existing refractive surgical techniques. Patients' desire for improved refractive surgical technology and surgeons' frustration with the status quo drove an enormous investment of time, energy, and capital into the development of excimer laser systems. The goal was to create a stable and accurate change of the corneal curvature with a predictably altered refractive state of the eye.

The barriers to the successful expression of excimer laser technology in ophthalmology were formidable and, to many, seemingly insurmountable. For example, calculations relating to laser physics demonstrated that the excimer laser would need almost 1 minute to remove an adequate amount of tissue from a myopic eye. Not only did the technology have to work, but it had to be extremely safe, with low biological and optical complications.

The first prototypic excimer laser system was shown at the American Academy of Ophthalmology (AAO) in 1987 and it generated great interest in radial keratotomy alternatives. There was also great resistance to the idea that anyone would touch the center of a normal cornea with a laser and disbelief that the procedure could ever be made safe enough to engender wide acceptance. The first successful PRK procedure, performed on a human eye in 1988 by Marguerite McDonald, MD, of New York, countered that disbelief.

Initially, the lack of immediate postoperative discomfort and the rapid rehabilitation of vision with LASIK pushed PRK into second place. Corneal thickness limitations and complications associated with the LASIK flap, however, renewed surgeons' interest in PRK around 2000. In particular, thinner-than-average corneas were contraindicated for LASIK because of their limitations regarding larger optical zones and wavefront-guided ablations. Interest in PRK, fueled by the necessity for deeper ablations, was further ignited by surgeons' recognition of the antihazing effect of topical mitomycin C, improved laser ablation algorithms, and better laser designs. These technical advances have increased the indicated range of PRK, improved the postoperative optical quality of corneas, and allowed PRK treatment in a number of patients whose refractive errors can be corrected with excimer laser corneal reshaping.

LASIK flap creation is not without significant risk. PRK that does not create corneal haze provides the patient and surgeon with a safer surgical alternative.

Excimer laser refractive surgery, which began as a hotly contested hypothesis based on a handful of animal experiments, has developed into a widely accepted technique used on millions of patients. This achievement is due to the many people who made extraordinary efforts to understand the nature of the interaction of far UV light with the cornea and develop the complex instrumentation that is now effectively used to correct human refractive errors.

Stephen L. Trokel, MD, is Professor of Clinical Ophthalmology at Columbia University, in New York City. Dr. Trokel states that he has no financial interest in the products or companies mentioned. He may be reached at trokel@columbia.edu.

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