Photorefractive Keratectomy (PRK)
Note: PRK is also known as Bladeless Laser (not bladeless LASIK) or Epi LASIK or Surface Ablation
In the PRK procedure, the corneal epithelium is first scraped off by the surgeon, and the laser is then used to precisely excise tissue from the Bowman’s membrane and the stroma.
In PRK, it usually takes 3-4 days for the epithelium to regenerate, and about 1-2 months for it to achieve its full thickness.
The corneal nerve endings reside in the epithelium. By scraping off the epithelium, these nerve endings get exposed. For the first 12-24 hours after PRK, therefore, there is really intense burning pain in the eyes. Painkillers and sedatives can help somewhat, but the pain is really quite uncomfortable. Vision is also compromised considerably for the first 3-4 days, and then also returns to the desired level only over several weeks, once the epithelium reaches full thickness. Further, since the epithelium is the eye’s primary barrier in preventing infection, after PRK, it is very important to take care for the first few days and weeks that the eye does not get infected.
Some cases with PRK can also get a haze on the cornea, accompanied by some regression of the treatment (i.e. some of the refractive error can come back). This usually happens when high refractive errors are treated (>-6D or > +4D). In low myopes, such haze and regression is rare. Most doctors use an extended period of steroid eye drops to prevent haze and regression. However, steroids have their own complications. A few doctors use a drug called Mitomycin-C to prevent haze and regression, especially if they are treating high myopia. However, Mitomycin-C is a highly potent drug, which can have unknown side effects over several years, and it seems unreasonable to use such a drug, especially when other alternative treatments, such as LASIK, are available.
Many variations of the basic technique of PRK are possible. They are known by various names, such as surface ablation, E-LASIK, Epi-LASIK, LASEK and Bladeless Laser. However, all these techniques suffer from the same basic issues as PRK-Pain in the first 24 hours, delayed vision recovery, susceptibility to infection, and possible haze and regression of the treatment.
When we started New Vision Laser Centers, all our patients underwent PRK. However, that has also made us aware of the limitations and disadvantages of PRK. We still perform PRK, but only in very specific indications, and only for low myopes.
Since it is the epithelium removal in PRK that is at the root of all the problems with the procedure, would it not be nice to have a procedure that would allow us to directly treat the stroma instead of treating it by first removing the epithelium?
That is where LASIK plays a role.