Photorefractive Keratectomy, or PRK, is a laser eye surgery designed to correct common vision problems, including astigmatism. Astigmatism is a refractive error where the cornea or the lens has an uneven, often oval shape, rather than a perfectly spherical one. This irregular curvature causes light to focus unevenly on the retina, resulting in blurred or distorted vision at any distance. PRK offers a method to permanently reshape the corneal surface, addressing the structural irregularity that causes this distortion.
The Mechanics of Astigmatism Correction via PRK
PRK corrects astigmatism by reshaping the cornea to make its curvature uniform. Astigmatism is often described as the eye being shaped like a rugby ball, featuring different curvatures along two main axes, or meridians. The goal of the PRK procedure is to sculpt this surface into a more symmetrically spherical shape, allowing light rays to converge at a single, sharp focal point on the retina.
An excimer laser accomplishes this reshaping, emitting ultraviolet light to precisely ablate, or vaporize, tissue. The laser’s application is guided by detailed preoperative measurements of the cornea’s topography, mapping the specific areas that require correction. Unlike correction for simple nearsightedness, astigmatism correction requires an asymmetrical tissue removal profile.
The excimer laser targets the steeper meridian of the cornea to selectively flatten it, while simultaneously adjusting the flatter meridian, equalizing the curvature across both axes. This ensures the resulting corneal surface is smooth and regular. The computer-guided process allows for customized treatment plans that account for the unique characteristics of each patient’s eye.
The PRK Surgical Process
The PRK procedure is performed on an outpatient basis and begins with topical anesthetic drops to numb the eye. A speculum is used to gently hold the eyelids open, preventing blinking during the process. Although the patient is awake, a mild sedative may be offered for relaxation.
The defining step of PRK is the removal of the corneal epithelium. This layer is removed either mechanically with a surgical brush or blade, or chemically using a diluted alcohol solution, exposing the underlying corneal tissue.
Once the surface is prepared, the patient focuses on a target light while the excimer laser is activated. The laser delivers rapid, cool pulses of energy to reshape the exposed corneal tissue. The application is brief, often lasting less than a minute per eye. Following treatment, a clear, soft bandage contact lens is placed over the eye to protect the treated area and aid in initial healing.
Success Rates and Limitations
PRK is an effective treatment for correcting astigmatism, particularly in mild to moderate prescriptions. For patients with low to moderate astigmatism, success rates show that 90 to 98% achieve visual acuity of 20/20 or 20/25. Over 99% achieve the 20/40 vision standard needed for driving without corrective lenses.
The procedure’s effectiveness has limitations when treating high degrees of astigmatism. Most surgeons consider PRK suitable for cylindrical prescriptions up to approximately 4.00 to 6.00 diopters. Treating higher prescriptions requires ablating more tissue, which can increase the risk of corneal haze or regression, where the eye partially reverts to its pre-surgical state.
A small percentage of patients may experience residual astigmatism after the initial procedure. Factors such as the individual patient’s healing response and the initial magnitude of the astigmatism influence the final outcome. An enhancement procedure may be considered, but the overall stability and long-term results of PRK are excellent for the majority of candidates.
The Post-Operative Healing Journey
The recovery following PRK is characterized by the removal of the epithelial layer. For the first three to five days after the procedure, patients experience moderate discomfort, including a gritty sensation, light sensitivity, and watery eyes. This is the period during which the epithelial cells regrow.
The bandage contact lens remains in place during this initial phase to minimize pain and facilitate the re-growth of the epithelium. Once the epithelial layer has fully healed, usually within the first week, the surgeon removes the bandage lens during a follow-up appointment. Though the surface is closed, vision remains blurry and fluctuating.
Visual stabilization is a gradual process that extends over several weeks to months. While many patients can resume driving and work within one week, final visual clarity may take three to six months. Throughout this period, patients must adhere strictly to a regimen of prescribed eye drops. These typically include antibiotics to prevent infection and anti-inflammatory medications to control haze and support healing.