Photorefractive keratectomy (PRK for short) is a method of refractive surgery. It is an alternative to LASIK, LASEK and more recent procedures such as ReLEx SMILE. In all of these procedures, the cornea of the eye is remodeled using a laser. The aim is to correct existing visual defects. The laser-assisted procedure is very precise and low-risk.
You can find further information and selected PRK specialists and centers here.
Photorefractive keratectomy (PRK) is a refractive surgery procedure. A laser removes parts of the cornea from the eye and reshapes its surface. The aim is to change the curvature of the cornea so that the patient can then see more clearly without a visual aid.
Keratomy is the removal of parts of the cornea. The descriptive adjective "photorefractive" refers to the optimization of the refractive properties of the cornea.
A sufficiently thick cornea is an essential prerequisite for performing a PRK. PRK can be used to correct visual defects such as short-sightedness and long-sightedness.
Photorefractive keratectomy is the oldest laser surgical procedure for correcting corneal refractive power. Surgeons were already working on the corneal surface in the 1960s and 1970s. However, they used mechanical instruments. These 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 the finest mechanical blade.
The first therapeutic applications of PRK took place in Germany in the late 1980s. Further developments of PRK are
As there is no incision in the corneal stroma as with Lasik, these procedures are also known as surface procedures.
The corneal surface is measured before treatment. The computer calculates the necessary material removal for modeling the new surface. The planned curvature of the new surface is intended to eliminate the current visual defect.
In the case of short-sightedness, the refractive power of the cornea and lens of the eye is too strong in relation to the length of the eyeball. In this case, tissue is removed from the center of the cornea to reduce the curvature.
With long-sightedness, the refractive power is too weak. Accordingly, tissue is removed from the edges of the cornea to increase the curvature.
In the case of an additional corneal curvature, the refractive power in one axis of curvature is changed from that in the axis at 90° to it.
As with LASIK and LASEK, PRK uses a computer-controlled combination of surgical microscope and laser device. The surgeon monitors the progress of the procedure on a monitor.
In preparation for the short operation, the eye is locally anaesthetized. The eyelids are held open with an eyelid retractor. The corneal epithelium, the thin top layer of the cornea, is then removed with a fine surgical blade.
The corneal tissue is now exposed. In the second step, the computer-controlled beam of the excimer laser remodels the surface point by point. Coupling with an eye tracking system ensures that the laser beam follows every eye movement.
The corneal tissue is vaporized without any significant release of heat. Neighboring tissue parts are therefore not damaged. The modeling is completed in about one minute.
The cornea is very sensitive after PRK. The patient is therefore given a therapeutic contact lens as a wound dressing. It protects the cornea and the corneal epithelium regenerates under the contact lens within a few days.
A combination of antibiotic and cortisone-containing eye drops and painkillers are also used.
The eyes can be treated in either one or two sessions .
During PRK, the cornea is processed and reshaped using a high-precision laser © RFBSIP | AdobeStock
After LASIK, the patient is often practically symptom-free just one day after laser eye surgery. Their visual acuity improves immediately after the treatment. With PRK, a slightly longer healing phase is to be expected.
In the first week after the procedure
are to be expected.
Visual impairment can last for several weeks. These include
The corneal epithelium grows back in about a week and you can remove the bandage contact lens. It usually takes three to four weeks before the final visual performance is achieved.
The final result of photorefractive keratectomy is as reliable as that of LASIK. Long-term side effects are even rarer.
The appearance of veils in the field of vision can be prevented by using mitomycin C: The chemotherapeutic agent is injected directly after PRK surgery. It prevents the uncontrolled proliferation 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.
With LASEK, the surgeon carefully removes the corneal epithelium with alcohol and pushes it aside. After the treatment, it is pulled back over the cornea. With LASIK, a so-called flap, a slightly thicker "lid", is cut out of the cornea and opened up. It is also put back in place after the treatment.
With PRK, the corneal epithelium is not spared and later reinserted, but removed.
By sparing the corneal epithelium in LASIK and LASEK, it was expected that healing would be accelerated after the procedure. There should also be less pain.
However, these expectations were not fulfilled. As a result, LASEK no longer offers any advantages over PRK and has therefore lost its significance.
After a LASIK procedure, vision recovers much faster than after PRK. There is also hardly any pain.
For some time, the LASIK procedure appeared to be the preferred method if the cornea was sufficiently thick. However, long-term observations show that the cornea suffers more severe and permanent damage than originally assumed. The flap can
even a long time after the operation or become detached again. Other, rarer complications of LASIK are
Furthermore, problems with the quality of vision occur somewhat more frequently after LASIK:
can significantly impair the results 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 dry eyes temporarily and, more rarely, permanently. In permanent cases, these symptoms can be very unpleasant.
PRK is suitable for anyone with defective vision with
who fulfill the general requirements for the feasibility of refractive laser surgery.
An essential prerequisite for performing PRK is a sufficiently thick cornea. A cornea that is too thin is considered a contraindication. The threshold value is a residual thickness of at least 250 µm after treatment, not including the epithelium (approx. 70 µm). This residual thickness is calculated from the corneal thickness minus the maximum ablation depth.
PRK should also not be performed in the case of chronically progressive corneal diseases. These include, for example
PRK would further worsen the clinical picture.
Recently, however, PRK has been combined with cross-linking (corneal stiffening) to correct defective vision. This shows good results.
Compared to LASIK and LASEK, PRK uses the cornea sparingly. It is therefore particularly recommended for patients with borderline corneal thickness. The LASIK flap can come loose in the event of a fall, impact or high acceleration. For this reason, PRK is recommended for people with a correspondingly increased risk, such as soldiers or athletes.
In 2007, LASIK dominated the market for refractory surgical procedures with a share of 85 percent. PRK only accounted for around 2 percent in Europe.
In 2014, LASIK and PRK were almost on a par, with around 40 and 35 percent respectively. This data comes from the European registry EUREQUO. Ophthalmologists from 14 countries voluntarily reported data from around 25,000 refractive surgery procedures between 2004 and 2014.
General risks associated with any type of refractive surgery are dry eye. Depending on the excimer laser profile, twilight and night vision may also be impaired due to
may occur. However, in the vast majority of cases, these complications disappear in the first few weeks after PRK.
The following can also occur after PRK
Thanks to modern eye tracking systems (eyetracker), decentration is now virtually impossible.
Keratectasia (isolated bulging of the cornea) can occur in less than 0.5 percent of cases. It must be treated by
be corrected.
Tear substitutes are necessary for the first 6 to 12 months to alleviate the symptoms of dry eyes. 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.
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