PRK - Photorefractive keratectomy-is the laser procedure intended to correct a refraction error, reducing dependency on glasses or contact lenses. PRK change the shape of the corneal surface using an eximeer laser to ablate (remove by vaporization) a small amount of superfitial stromal tissue. The outer layer of the cornea is removed prior to the ablation. The outer layer - epithelium, is a soft, rapidly regrowing layer completely replace itself from limbal stem cells within a few days with no loss of clarity.
Unlike LASIK,PRK does not involve a knife, microtome, or cutting laser, but there may be more postop pain and slower visual recovery to maximal result (up to 4-6 weeks).
Unlike LASIK, PRK does not have an increased risk of dislocated corneal flap, which may occur with trauma after LASIK.
Although PRK and LASEK are similar techniques, there are minor differences between them. In PRK, epithelium is removed (mechanicaly, with higher stress for corneal tissue, more proinflamatory agents aer released during this action, higher risk of haze) and the outermost layer below the epithelium is treated with laser. In LASEK, epithelium is not removed, but an alcoholic solution is used to cause the epithelial cells to weaken; the surgeon will fold the epithelial layer out of the laser treatment field, and fold it back in its original place after the cornea has been reshaped by the laser.
PRK, like LASEK, is more reccomended for persons with increased risk of eye injury (builders, welders, policemens, soldiers, prof. sportsmens and etc.) or with low diopters (up to 3.0D).
There are a basic criteria which a potential candidate should satisfy:
- Normal ocular health
- Age 18 years or older
- Stable refraction error (no noticeable change in the last year) correctable to 20/40 or better
- Between −0.5 to −3.00D of Myopia (for higher diopters recommended to use Mitomycin C)
- Not pregnant at the time of surgery
- Realistic expectations of the final results (with a complete understanding of the benefits, as well as the possible risks)
- Pupil size may be bigger than in LASIK patients
There are also some pre-existing conditions that may complicate or preclude the treatment.
- Collagen/vascular diseases
- Ocular disease (e.g.,keratoconus, glaucoma)
- Systemic disorders (e.g. diabetes, rheumathoid arthritis)