What is photorefractive keratectomy (PRK)?
Photorefractive keratectomy (PRK) is laser eye surgery that reduces the need for corrective eyewear by reshaping the cornea of the eye, thereby changing the way the eye focuses light on the retina. An excimer laser ablates (removes) a thin layer of the cornea at its surface, changing the cornea's refractive (focusing) power.
LASIK (laser-assisted in-situ keratomileusis) eye surgery is a similar procedure except first a medical professional creates a flap within the cornea with either a laser or a microkeratome blade and then performs the ablation below the flap, deeper in the cornea. In LASEK (laser-assisted subepithelial keratomileusis), a medical professional makes a thinner flap of just the outer layer (epithelium) and performs the ablation under the epithelium. There are pros and cons to weigh in choosing between LASIK, LASEK, and PRK. In terms of cost, photorefractive keratectomy is usually less expensive than LASIK. Postoperative discomfort is typically less of an issue with LASIK. Ultimately, the choice comes down to which procedure will produce the most safe and reliable outcome, and factors such as corneal health and degree of refractive error determine this.
What vision problems does photorefractive keratectomy treat?
PRK can treat a variety of refractive errors, including myopia (nearsightedness), hyperopia (farsightedness), and astigmatism (imperfection in the eye's curvature of the cornea or lens). The laser treats certain medical conditions affecting the eye's surface (for example, Salzmann's nodules and recurrent erosions). When physicians use the laser for these indications, the procedure is referred to as phototherapeutic keratectomy (PTK).
Who is a good candidate for PRK?
The ideal candidate is someone whose corneal tissue is well suited for the procedure. Patients must first meet several criteria. For example, corneal thickness is important. Larger corrections require more tissue ablation so thin corneas may not be suitable for refractive surgery, particularly in patients with very high myopia. The surgeon will calculate if there will be sufficient residual corneal tissue to perform the ablation safely.
The eye doctor reviews the medical history and performs a complete eye examination to look for any eye problems or medical conditions that might affect the outcome of refractive surgery. Poor eye health or certain medical diseases (for example, uncontrolled diabetes) may increase the risk of a poor outcome.
Age is another factor. If a candidate's eyes are still growing (for example, in childhood and in the teen years), the refractive error may not have stabilized. Undergoing photorefractive keratectomy too soon may only provide a temporary correction of the refractive error, since the eye is still changing.
Photorefractive Keratectomy and Other Eye Surgeries
What Is Laser Vision Surgery?
Excimer laser refractive surgery, commonly known as laser vision correction, has been around for the past 20 years. This procedure is performed to reduce or eliminate the need for glasses or contact lenses.
What are the potential side effects and complications of PRK?
Common side effects in the days following the PRK procedure include discomfort, dry eye, foreign body sensation (gritty or sandy feeling), blurred vision, and glare or haloes around lights. These symptoms tend to resolve as the eye heals. Visual recovery takes a few days, and the final uncorrected visual acuity (vision without glasses) typically stabilizes after a few months.
Long-term under-correction or overcorrection can result from variable healing rates, inaccuracies in calculations, or unstable refractive errors.
Uncommon but potentially serious complications include infection, irregular shape, and thinning of the cornea (ectasia), elevated intraocular pressure (sometimes related to postoperative steroid eyedrops), scarring, or persistent corneal erosions. These complications could result in visual blurring or glare, vision loss, light sensitivity, or pain. These complications have become less common with improvements in preoperative screening, more sophisticated laser ablation profiles, and better medication regimens for optimized healing.
How do I prepare for PRK?
The eye surgeon first determines if your eyes are suitable for PRK surgery in the preoperative screening.
You may be asked to refrain from wearing hard (rigid) contact lenses for up to several weeks or soft contact lenses for several days in preparation for both the preoperative screening and the procedure itself. This is important because contact lenses can temporarily reshape the cornea. You will want your cornea to be in its “natural,” unaltered state when being measured preoperatively and when being treated.
On the day of PRK surgery, do not wear makeup or perfume. Be sure to have your postoperative medications ready and review the instructions for their use.
Recognize These Common Eye Problems
What happens during the PRK procedure?
Typically, the patient lies on his/her back. A small lid speculum holds the eyelids open. Once the eye is numbed with anesthetic drops, the surgeon removes the outer layer (epithelium) of the cornea either mechanically (with a tiny brush or a sweeping tool) or with laser. Once the surgeon removes the epithelium, laser is applied to the surface of the cornea to precisely ablate (remove) a thin layer of corneal tissue based on the amount of myopic, hyperopic, or astigmatic correction desired. A clicking or tapping sound might be heard as the laser fires. Once the laser ablation is complete, the surgeon places a contact lens. Medical professionals remove this "bandage" contact lens once the epithelium heals, typically a few days later (about three to five days). The postoperative medicated eye drops are used with the contact lens in place.
What follow-up care do people need after PRK? What is the recovery time for PRK?
At the completion of your surgery, you will need someone to drive for you. You can expect to be very light sensitive, so be sure to have sunglasses with you.
Medical professionals will instruct you to use prescription medicated eyedrops afterward. These may include steroids, anti-inflammatory drugs, and antibiotics. The drops are very important for healing well. They serve to control inflammation and prevent infection, as well as to minimize discomfort.
You can expect a mild to moderate amount of eye pain (light sensitivity, foreign body sensation) for the first few days as the epithelium heals. You may need to take oral medication for pain.
Close monitoring of the healing process is also very important. Be sure to keep all scheduled follow-up appointments. The number and frequency of follow-up visits will depend on how quickly the eye heals. It may take several weeks to three months to reach your best corrected vision (stable refraction).
What is the prognosis after a photorefractive keratectomy?
Generally, the success rate is very good. Assuming there are no underlying medical conditions that could adversely affect the healing process, the surface of the eye (epithelium) usually heals in a few days, achieving a stable refraction in the weeks and months following the procedure. Because the surgeon made no flap, there are no concerns about the flap-related complications sometimes seen after LASIK surgery.
Over time, there may be a need to use corrective eyewear again, either because some of the corrective effect regresses or because the underlying refractive error was still in flux and had not stabilized completely prior to the procedure. Re-treatment with further photorefractive keratectomy is often possible at a later date.
Patients over the age of 40 who correct their distance vision with photorefractive keratectomy will still need to use reading glasses when presbyopia sets in. Presbyopia is the inability to see well close-up due to age-related changes in the eye's lens. Patients over 40 who already have presbyopia can opt to have one eye corrected for distance while having the other eye corrected for near. This is called "monovision." The eye doctor will discuss these options with you in the preoperative screening.
The colored part of the eye that helps regulate the amount of light that enters is called the:
Mifflin, M.D., et al. "Efficacy and safety of a 3-month loteprednol etabonate 0.5% gel taper for routine prophylaxis after photorefractive keratectomy compared to a 3-month prednisolone acetate 1% and fluorometholone 0.1% taper." Clin Ophthalmol 11 (2017): 1113-1118.
O'Brart, D.P. "Excimer laser surface ablation: a review of recent literature." Clinical & Experimental Optometry 97.1 (2014): 12-17.
Woreta, F.A., et al. "Management of post-photorefractive keratectomy pain." Survey of Ophthalmology 58.6 (2013): 529-535.