Photorefractive Keratectomy (PRK) is a vision correction procedure that uses laser technology to reshape the cornea, the transparent front surface of the eye. This surgery corrects common refractive errors such as nearsightedness, farsightedness, and astigmatism. By altering the cornea’s curvature, PRK enables the eye to properly focus light onto the retina, reducing or eliminating the need for glasses or contact lenses. The history of PRK is closely tied to the discovery of a specific type of laser that provided the necessary precision for corneal tissue removal.
The Initial Breakthrough and Timeline
The foundational work that made PRK possible began in the early 1980s, when researchers first recognized the unique properties of the excimer laser for biological tissue. In 1981, physicist Rangaswamy Srinivasan, working at IBM, demonstrated that the excimer laser could etch organic material with precision. His discovery showed that the laser could remove tissue without causing thermal damage to the surrounding area, a process he termed ablative photodecomposition.
Ophthalmologist Dr. Stephen Trokel quickly recognized the potential of this technology for corneal surgery. He and colleagues published an influential paper in 1983 detailing the first application of the excimer laser on corneal tissue. This research established the concept of using a laser to change the eye’s refractive power by sculpting the corneal surface.
The first human eye treatment using PRK was performed in 1987 by Dr. Theo Seiler in Germany. The first successful PRK procedure in the United States on a sighted eye was completed by Dr. Marguerite McDonald in 1988. After years of clinical trials, the United States Food and Drug Administration (FDA) formally approved the PRK procedure for vision correction in 1995.
Technological Foundation: The Excimer Laser
The success of PRK depends upon the excimer laser. This device produces a beam of ultraviolet (UV) light, specifically at a 193-nanometer wavelength. The UV energy is absorbed by the corneal tissue, causing the precise breaking of molecular bonds, which is the mechanism of “photoablation”.
This photoablative process enables the laser to vaporize and remove microscopic layers of tissue without generating heat that would damage adjacent cells. The controlled nature of this tissue removal allows for the fine adjustments needed to correct vision errors. For instance, correcting one diopter of nearsightedness requires removing a layer of tissue only about 10 to 12 microns thick.
Evolution of Refractive Surgery
PRK served as the direct predecessor for subsequent advancements in laser vision correction, most notably Laser-Assisted In Situ Keratomileusis (LASIK). LASIK emerged in the early 1990s, building upon the excimer laser technology developed for PRK. The primary procedural difference lies in how the deeper corneal tissue is accessed for reshaping.
In PRK, the surgeon removes the thin, outermost layer of the cornea, the epithelium, before applying the excimer laser to the underlying tissue. Conversely, LASIK involves creating a hinged flap of corneal tissue that is lifted to allow the laser to reshape the inner layer, after which the flap is repositioned. This flap technique is why LASIK typically offers a faster initial recovery time with less post-operative discomfort.
Despite the faster recovery associated with LASIK, PRK remains a preferred procedure for certain patients today. Because PRK does not require the creation of a flap, it is a safer option for individuals with corneas that are too thin for LASIK. It is also the recommended choice for people whose jobs or hobbies involve a high risk of eye trauma, such as contact sports, as there is no flap that could become dislodged later.