Keratomileusis and the Excimer Laser
Part 2 of a 4-Part Series
Although Radial Keratotomy was the more widely practiced refractive procedure in the United States, it was not the first. This accolade is instead reserved for keratomileusis. In keratomileusis, part of the cornea is removed and then the cornea is reshaped using a blade in order to correct refractive errors.
As with R.K., keratomileusis was stumbled upon, as an incidental finding, when Dr. Barraquer performed a corneal transplant on a patient with keratoconus. Keratoconus is a degenerative corneal disease which is characterized by thinning and cone-shaped protrusion of the central cornea. Therefore, keratoconus-afflicted corneas are typically steep centrally. Since healthy corneal tissue is flatter, the corneal transplant flattened the cornea, which caused a reduction in myopia, or nearsightedness. Subsequent to this finding, Dr. Barraquer spent many years experimenting with different surgical techniques for the correction of myopia. He held his first course in Refractive Keratoplasty at the Barraquer Institute in Columbia in 1977. Seventeen of these courses were held at the institute until 1984.[ii]
In 1981, in the U.S., the physicist Rangaswamy Srinivasan discovered that the ultraviolet-light-based excimer laser could be applied in etching or drilling organic solids, including human tissue, without causing thermal damage to the surrounding area.[iii] In 1983, he began collaborating with ophthalmic surgeon Stephen Trokel, M.D. Together they developed the excimer laser used in refractive surgery today. This is a cold ultraviolet laser used to reshape the cornea. The laser uses UV light to remove microscopic amounts of corneal tissue. Its precision is at the level of a micron.
In 1985, Dr. Mandel was part of the first team, along with Dr. Trokel, proving that the excimer laser was effective in refractive surgery. Based on Dr Mandel’s work, he won the WIlliam Warner Hoppin Award from the New York Academy of Science and was recruited to Harvard’s Laser Laboratory to work on the next generation of research: large area ablation (PRK). Dr. Mandel’s work, which was the first paper proving that the excimer laser works in current laser vision correction techniques, was presented in 1987 at the leading ophthalmologic research association (ARVO).
The first refractive procedure performed with the excimer laser was PRK (Photo-Refractive Keratomileusis), which was approved by the FDA in 1996 to treat nearsightedness[iv]. FDA approval for farsightedness and astigmatism soon followed.
In the PRK procedure, the epithelium is gently removed using a specialized epithelial brush. The cornea beneath is then reshaped using the excimer laser. A bandage soft contact lens is placed on the eye to allow the epithelium of the cornea to regenerate, which typically takes 72 hours. Although vision is functional and patients usually go back to work the next day, vision is slightly blurry and the visual recovery period for PRK is generally 7 to 10 days. Optimal vision then slowly returns over the next several months.
PRK is one of the technologies still utilized today for some patients who are not candidates for LASIK. These patients include those with both thin corneas and high levels of nearsightedness. The end results of PRK are just as good as LASIK. Thus, the determining factor for patients who are candidates for both procedures is convenience. In our world of immediate gratification, LASIK is the winner as optimal vision is achieved the morning after the procedure.