Photorefractive Keratectomy

Introduced in 1987, photorefractive keratectomy (PRK) is the oldest technique in ophthalmology for correcting a refractive anomaly (nearsightedness and farsightedness) or astigmatism (astigmatism) with the use of laser treatment. PRK is still used especially in patients with a small corneal thickness (corneal thickness) or in people who work in professions where it is necessary to have an optimal visual acuity (visual acuity) without visual aids. Before the procedure, however, it must be ruled out that the patient suffers from an eye disease, such as sicca syndrome (autoimmune disease; the symptom “dry eye” occurs when the tear fluid is not produced sufficiently or is not composed optimally for the eye). Following the examination, the surgeon must decide whether the use of refractive surgery (this generic term stands for all surgical procedures on the eye to correct a refractive anomaly so that the use of glasses or contact lenses is no longer necessary) is nevertheless possible in the case of a present disease.

Indications (areas of application)

  • Correction of small to moderate myopia – myopia, up to -6 dpt.
  • Correction of myopic astigmatisms – corneal curvature in combination with myopia, up to -6 dpt.
  • Patients who, despite wearing a visual aid, do not have an optimization of Visuś (visual ability) (eg, anisometropia / condition of different refractive ratios of the left and right eye).
  • Intolerance for contact lenses (possibly due to sicca syndrome – dry eye).
  • Need for a corrected Visuś without the use of an additional visual aid.

In addition, PRK can also be used to remove superficial scars or pathological changes in the cornea. It is then called PTK (phototherapeutic keratectomy). As mentioned above, correction of mild astigmatism is also possible by PRK.

Contraindications

The surgical procedure

PRK belongs to the genus of refractive surgery and is used to correct refractive anomalies and an astigmatism. The treatment is not allowed in underage patients! The procedure is as follows:

  • Before the actual treatment, which is very likely to result in the correction of refractive errors, the patient is locally anesthetized with the administration of eye drops (the patient is fully conscious and witnesses the laser procedure; at the request of the patient or on the orders of the doctor, there is the possibility of taking sedatives).
  • After this step, the attending physician inserts an eyelid retractor to ensure that the patient cannot perform involuntary (non-influenceable) eyelid closure.
  • In the following step, PRK is fundamentally different from LASIK (Laser In Situ Keratomileusis): While in LASIK the patient has sharp vision immediately after the operation without pain, because the procedure is performed under the corneal surface, which is sensitive to pain, and the epithelium (superficial area of the cornea, which consists of several parts and is adjacent to the tear film of the eye; no part of the cornea is perfused, so the procedure can be performed without the occurrence of bleeding) does not need to be removed, unlike PRK. In PRK, a scraping instrument is used to remove the corneal epithelium in the center of the cornea.
  • In the further course, treatment is then carried out with the excimer laser (this generates electromagnetic radiation, which is used for the surgical treatment of refractive anomalies).Photoablation (ablation of tissue) with the help of the laser corrects the previously detected refractive error. Here, the light of the laser penetrates less than 0.1 mm into the cornea and, due to the precise laser application, achieves a tissue ablation of less than 0.5 mm. The excimer laser procedure is performed with a scanning spot system, which results in a laser beam with a very small diameter of approximately 1 mm gliding across the cornea. Depending on the type of refractive error, there are different settings on the PC, according to which the ablation of tissue works. If the result of PRK is not optimal, there is the possibility of repeating the procedure, so that the desired result can still be achieved.
  • As with other refractive surgery procedures, PRK uses the eye-tracking system (method of tracking the patient’s gaze) and provides the surgeon with the ability to respond to involuntary eye movements, so that the result of the procedure is not affected.
  • If there is an indication (“indicated” of a certain treatment, i.e., healing indication) for the procedure on the other eye, it must not be treated on the same day, because a bilateral eye bandage would be problematic. Furthermore, the vision after PRK increases only after a few days.The epithelium generally heals completely after a few days and leads in, for example, 95% of myopia to – 4 dpt to the therapeutic goal.

Possible complications

  • Prolonged wound healing phase
  • More pain compared to other laser eye procedures because PRK is a laser procedure that completely removes the epithelium (superficial layer of tissue in the eye)
  • Feeling of dryness and possible inflammation of the eye during the healing process.
  • Higher risk of scarring as a result of the procedure compared with LASIK or Lasek.
  • Short-term and long-term over- or under-correction of visual impairment.
  • Haze (haze on the cornea).

Benefit

PRK offers patients the opportunity to opt for a tissue-sparing procedure, as only the epithelium needs to be removed compared with LASIK. In particular, the low complication rate of PRK and the at least equivalent results compared with other refractive surgery procedures, allow this technique to be used more than 20 years after its introduction.