Photorefractive Keratectomy (PRK)
Until recently, if you were one of the millions of people with a refractive error-light rays not focusing precisely on the retina-eyeglasses and contact lenses were the only options for correcting vision. But with the arrival of refractive surgery, some people may have their vision corrected through surgery. Photorefractive keratectomy (PRK) is one of several refractive surgery procedures used by ophthalmologists to permanently change the shape of the cornea to improve the way it focuses light on the retina.
PRK is an outpatient procedure, done under topical anesthetic eyedrops. It takes about fifteen minutes. The epithelium, the outer cell layer of the cornea, is removed with a blade, alcohol or a laser. An excimer laser, which produces ultraviolet light and emits high-energy pulses, is used to remove a thin layer of corneal tissue. Your ophthalmologist enters your vision correction information in a computer and the laser beam vaporizes the surface of the cornea up to that precise depth. By breaking the bonds that hold the tissue molecules together, your cornea is reshaped, correcting the refractive error. Because no incisions are made, the procedure does not weaken the structure of the cornea.
Immediately following surgery the eye is patched or a bandage contact lens is placed on the eye. After PRK vision is blurry for 3 days to one week. It may take a month or longer to achieve one’s best vision. Patients may be on eyedrops for up to three months.
Possible complications of PRK surgery include undercorrection, overcorrection, poor night vision and corneal scarring. Permanent vision loss is very rare. In recent studies monitored by the FDA, 95% of eyes were corrected to 20/40, the legal limit for driving without corrective lenses in most states.
To be a candidate for the procedure you must have a stable and appropriate refractive error, be free of eye disease, be at least eighteen years old and be willing to accept the potential risks, complications and side effects of PRK.
Phototherapeutic Keratectomy (PTK)
Intracorneal rings are plastic inserts placed in the cornea. The rings flatten the central cornea to PTK is an excimer laser surgical procedure that removes roughness or cloudiness from the cornea. The cornea is the smooth clear window of the eye in front of the colored iris that helps bend light rays so they focus directly on the retina, the light-sensing layer of cells at the back of the eye. If the corneal surface is rough or cloudy, the rays of light do not focus properly on the retina and images are blurry.
Until recently, the rough cornea was scraped smooth with a surgical blade, while the cloudy cornea required a partial or full corneal transplant. More recently, phototherapeutic keratectomy, or PTK, is an option.
The excimer laser allows some abnormal corneas to be treated with a cool beam of light that evaporates tissue. The principal advantage of laser surgery over conventional surgery is the laser is able to create a smoother corneal surface than a blade and smaller amounts of tissue can be removed.
Potential complications after PTK include poor wound healing, excessive corneal flattening resulting in farsightedness, and irregular astigmatism or poor vision that cannot be corrected completely with glasses.
Radial Keratotomy (RK)
Radial keratotomy (RK) is surgical procedure that has been used since the late 1970′s to reduce myopia by changing the curvature of the cornea.
Using a microscope, microsurgical instruments and a diamond blade, the surgeon makes several deep incisions (keratotomies) in the cornea in a radial or spoke-like pattern. People with myopia have difficulty with distance vision because the cornea has too much power and focuses light rays in front of the retina. RK weakens the support of the cornea, flattening it and reducing its power. This allows the light rays to focus directly on the retina.
RK takes fifteen minutes and may be performed with the patient awake. Eyedrops anesthetize the cornea, eliminating pain during the procedure. Following surgery, people are moderately uncomfortable and often require oral pain medication. Antibiotic eyedrops need to be taken for approximately one week. Clear vision can be present the day following surgery.
Postoperative complications include glare, halos, undercorrection, overcorrection and astigmatism that may not be able to be corrected with glasses. The major disadvantage of RK compared to laser procedures is it permanently weakens the cornea. Radial keratotomy is currently being used to correct low levels of myopia.