Photorefractive keratectomy (PRK) is a type of refractive surgery. During the procedure, a laser removes portions of the cornea and reshapes its surface. The goal is to alter the curvature of the cornea so that the patient can see more clearly without visual aids afterward.
“Keratectomy” refers to the removal of corneal tissue. The descriptive adjective “photorefractive” refers to the optimization of the cornea’s light-refracting properties.
A sufficiently thick cornea is an essential prerequisite for performing PRK. PRK can be used to correct refractive errors such as nearsightedness and farsightedness.
Photorefractive keratectomy is the oldest laser surgical procedure for correcting corneal refractive power. As early as the 1960s and 1970s, surgeons were already treating the corneal surface. However, they used mechanical instruments for this purpose, which are significantly less precise.
The invention of the excimer laser was a prerequisite for PRK. Its high-energy UV pulses can ablate biological tissue more precisely than even the finest mechanical blade.
The first therapeutic applications of PRK took place in Germany in the late 1980s. Further developments of PRK include
Since no incision is made into the corneal stroma, as is the case with LASIK, these procedures are also referred to as surface procedures.
Before treatment, the corneal surface is measured. The computer calculates the amount of tissue that needs to be removed to shape the new surface. The planned curvature of this surface is designed to correct the current vision defect.
In the case of nearsightedness, the refractive power of the cornea and the eye’s lens is too strong relative to the length of the eyeball. Here, tissue is removed from the center of the cornea to reduce its curvature.
In the case of farsightedness, the refractive power is too weak. Accordingly, tissue is removed from the peripheral areas of the cornea to increase its curvature.
If astigmatism is also present, the refractive power is altered along one axis of curvature differently than along the axis perpendicular to it (at 90°).
As with LASIK and LASEK, PRK uses a computer-controlled combination of a surgical microscope and a laser device. The surgeon monitors the progress of the procedure on a screen.
In preparation for the brief surgery, the eye is anesthetized locally. The eyelids are held open with an eyelid retractor. Then the corneal epithelium—the thin outermost layer of the cornea—is removed with a fine surgical blade.
The corneal tissue is now exposed. In the second step, the computer-controlled beam of the excimer laser reshapes the surface point by point. Integration with an eye-tracking system ensures that the laser beam follows every eye movement.
The corneal tissue is vaporized without significant heat release. Therefore, adjacent tissue is not damaged. The reshaping is completed in about one minute.
The cornea is very sensitive after PRK. Therefore, the patient is fitted with a therapeutic contact lens to act as a protective dressing. It protects the cornea, and the corneal epithelium regenerates beneath the contact lens within a few days.
In addition, a combination of antibiotic, corticosteroid, and pain-relieving eye drops is administered.
The eyes can be treated in either one or two sessions.
In PRK, the cornea is treated and reshaped using a high-precision laser © RFBSIP | AdobeStock
After LASIK, patients are often virtually symptom-free just one day after the procedure. Their vision improves immediately following treatment. With PRK, a slightly longer healing period is to be expected.
In the first week after the procedure, you can expect
- pain,
- burning eyes,
- a foreign body sensation, and
- sensitivity to light
.
Vision problems may last for several weeks. These include, for example,
- blurred and/or hazy vision,
- sensitivity to glare, and
- halos.
The corneal epithelium regenerates in about a week, at which point you may remove the protective contact lens. It usually takes three to four weeks to achieve final visual acuity.
The final outcome of photorefractive keratectomy is just as reliable as that of LASIK. Long-term side effects are even less common.
The occurrence of haze in the visual field can be prevented by using mitomycin C: This chemotherapy drug is instilled immediately after PRK surgery. It prevents the uncontrolled growth of scar tissue on the corneal wound. In this way, it ensures a more orderly healing process.
PRK, LASEK, and LASIK differ in the first phase of laser treatment.
In LASEK, the surgeon gently loosens the corneal epithelium with alcohol and pushes it aside. After the treatment, it is repositioned over the cornea. In LASIK, a so-called flap—a slightly thicker “lid”—is cut from the cornea and lifted. It, too, is repositioned after the treatment.
In PRK, the corneal epithelium is not preserved and later repositioned, but rather removed.
It was expected that preserving the corneal epithelium in LASIK and LASEK would lead to faster healing after the procedure. It was also expected to result in less pain.
However, these expectations were not met. As a result, LASEK no longer offers any real advantages over PRK and has consequently lost its significance.
After a LASIK procedure, vision recovers much more quickly than after PRK. There is also hardly any pain.
As a result, the LASIK procedure appeared for some time to be the preferred method when corneal thickness was sufficient. Long-term observations, however, show that the cornea sustains more severe and lasting damage than originally assumed. The flap can
- be damaged by impacts,
- high acceleration, and
- other stresses
suddenly shift or detach again, even long after the surgery. Other, rarer complications associated with LASIK include
- epithelial cells growing under the flap, which cloud the cornea, as well as
- dangerous inflammation in the deeper layers of the cornea caused by invading bacteria.
Furthermore, problems with visual quality occur somewhat more frequently after LASIK:
- sensitivity to glare and
- halos around light sources
can significantly impair the outcome of laser eye surgery despite optimal visual acuity. In addition, corneal nerves can be damaged when the flap is cut during LASIK. This very often leads to temporary dry eyes and, less frequently, to permanent dry eyes. In permanent cases, these symptoms can become very uncomfortable.
PRK is suitable for anyone with
- myopia (nearsightedness) up to approximately -6 diopters
- hyperopia (farsightedness) up to approximately +3 diopters
- astigmatism (corneal curvature) up to +/- 3 diopters
who meet the general requirements for refractive laser surgery.
A key requirement for performing PRK is a sufficiently thick cornea. A cornea that is too thin is considered a contraindication. The threshold is a residual thickness of at least 250 µm after treatment, not including the epithelium (approximately 70 µm). This residual thickness is calculated by subtracting the maximum ablation depth from the corneal thickness.
PRK should also not be performed in cases of chronic, progressive corneal diseases. These include, for example,
PRK would cause the condition to worsen further.
Recently, however, PRK has been combined with cross-linking (corneal stiffening) to correct refractive errors. This approach has shown good results.
Compared to LASIK and LASEK, PRK is less invasive to the cornea. For this reason, it is particularly recommended for patients with borderline corneal thickness. The LASIK flap can detach in the event of falls, impacts, or high acceleration. For this reason, PRK is recommended for individuals with a correspondingly increased risk, such as soldiers or athletes.
PRK is also becoming increasingly popular among ophthalmologists and patients for this reason. In 2007, LASIK dominated the market for refractive surgery procedures with an 85 percent share. PRK accounted for only about 2 percent in Europe.
By 2014, LASIK and PRK were almost neck and neck, at around 40 percent and 35 percent, respectively. These data come from the European registry EUREQUO. Between 2004 and 2014, ophthalmologists from 14 countries voluntarily reported data on approximately 25,000 refractive surgery procedures.
General risks associated with any type of refractive surgery include dry eye. Depending on the excimer laser profile, there may also be a reduction in twilight and night vision due to
- reduced contrast sensitivity,
- glare (glare effects), and
- halos
may occur. However, in the vast majority of cases, these complications resolve within the first few weeks after PRK.
In addition, the following may occur after PRK:
- short- to long-term over- or undercorrections, as well as
- a reduction in best-corrected visual acuity due to ablation decentration (very rare).
Thanks to modern eye-tracking systems, decentration is virtually impossible today.
In less than 0.5 percent of cases, keratectasia (isolated bulging of the cornea) may develop. It must be treated with
- cross-linking or,
- if no other option is available, keratoplasty (corneal transplant)
.
Artificial tears are necessary for the first 6 to 12 months to relieve symptoms of dry eye. This also applies to all other refractive procedures.
Contact sports such as (kick)boxing, karate, etc., should be avoided for the first 6 weeks if possible. Driving is possible again about 4 to 6 weeks after PRK.
The PRK method is a proven procedure in refractive surgery and is considered minimally invasive, as it does not involve any incisions. In this treatment method, the surface of the cornea is ablated; more precisely, the outermost layer of the cornea—the epithelial layer—is removed. A high-precision laser, usually an excimer laser, then reshapes the cornea to optimize the eye’s refractive power. This makes PRK particularly suitable for patients with thin corneas and a good alternative to LASIK.
Compared to LASIK or LASEK, PRK and LASEK offer certain advantages over flap-based procedures, even though the healing process takes slightly longer. Dry eyes may occur in the first few weeks after PRK, which is why a therapeutic contact lens is often used. Nevertheless, many patients report a significant improvement in their vision and appreciate the possibility of living without glasses or contact lenses. The method is particularly suitable for people who no longer wish to use traditional vision aids.
Even when compared to modern procedures such as RELEX SMILE, SMILE Pro, and Femto-LASIK, PRK remains a viable option. PRK was the first successful laser eye surgery technique and remains an established procedure in refractive surgery to this day. While LASIK involves creating a flap, PRK removes the outermost layer of the cornea, eliminating the need for any incisions.
Despite its many advantages, the general risks associated with any type of refractive treatment should be taken into account. A thorough preliminary examination of both eyes is an essential prerequisite for the procedure. The healing process may vary during the first month, but in the long term, PRK provides stable correction of refractive errors. Overall, it is clear that PRK remains a viable and effective method for achieving a long-term life without glasses or contact lenses through laser eye surgery.
What exactly is PRK?
PRK stands for photorefractive keratectomy and is one of the oldest procedures in refractive surgery. During the procedure, the outermost layer of the cornea is removed and then reshaped using an excimer laser to correct the refractive error.
Who is a good candidate for PRK?
PRK is particularly suitable for patients with thin corneas or for individuals for whom LASIK is not an option. PRK is also often preferred for those with specific occupational requirements.
What is the difference between PRK, LASEK, and LASIK?
The main difference is that LASIK involves creating a flap, whereas PRK and LASEK involve removing or displacing the outermost layer of the cornea. As a result, PRK is gentler on the eye, but the healing process takes slightly longer.
How long does recovery take after PRK?
The recovery process after PRK typically takes several days to weeks. Discomfort may occur in the first few days, which is why eye drops and a therapeutic contact lens are used.
What are the risks of PRK?
As with any surgery, PRK carries potential complications such as dry eyes or delayed healing. Overall, however, PRK is considered a safe and precise method of laser eye surgery.
