Photorefractive Keratectomy (PRK) or Surface Ablation or LASEK or E-LASIK
Photorefractive Keratectomy (PRK) is the oldest way to perform laser vision correction. It is also called Surface Ablation, LASEK or E-LASIK or Advanced Surface Ablation (ASA). More on these terms later.
As in all forms of Laser Vision Correction, PRK also involves corneal reshaping. Tiny amounts of corneal tissue are removed to give the cornea a new shape, and thereby a new focusing power.
In PRK or Surface Ablation, the epithelial cells (the front cells) of the cornea are removed (either mechanically, or using dilute alcohol to kill and loosen the cells), and the inner layer of the cornea is exposed. It is important to remove the epithelial cells, since these cells have the ability to regrow. In case the epithelial cells are exposed to the laser, there will be a temporary correction of the refractive error, but as over a few days the epithelial cells regrow, the refractive error will come back. So it is important to first remove the epithelial cells.
Once the epithelial cells are removed, the remaining cornea is exposed to the excimer laser, and the cornea given a new shape. A bandage or a contact lens is then placed on the eye, and the epithelial cells are allowed to regrow. Once the epithelial cells reach full thickness, proper correction is achieved.
PRK or Surface Ablation is otherwise a very safe technique. However, it does suffer from some disadvantages that you must be aware of:
a) There is a lot of pain immediately following the procedure for the first 24 hours. This can lead to a lot of discomfort.
b) It takes a while for full vision recovery to come about. So you may not see clearly for a week to a few weeks, depending on your healing process
c) In some case, especially those with high numbers, there can sometimes be a rather uncontrolled healing. In such a case, there is corneal haze and regresssion of the treatment (i.e. the number comes back), even months or years after the treatment
d) To control the healing reaction, steroid drops are prescribed for a few weeks to months. Steroid drops have there own side effects in some people, including rise of early cataract and rise of the pressure within the eye.
Some doctors use Mitomycin-C, a powerful anti metabiolite to check the uncontrolled healing. However Mitomycin-C has its own problems, and can sometimes cause scarring and extremely delayed visual recovery.
The different terms are all referring to the same process. E-LASIK, LASEK and Advanced Surface Ablation usually refer to alcohol being used to kill and loosen the epithelial cells, and then there removal as a sheet, as opposed to mechanically. Sometimes this sheet is replaced after healing, which makes life even worse.
Some surgeons also do transepithelial PRK, in which the laser is first used to remove the epithelium, and then the real laser treatment is initiated.
Notwithstanding its disadvantages, PRK or Surface Ablation has a role in the armamentarium of laser vision correction, and is appropriate for specific cases. Your New Vision Doctor will explain you the possible role of PRK or surface ablation in your particular case
Epi LASIK (Surface Ablation) with AMADEUS Microkeratome [www.keepvid.com]
For More Information on PRK or Surface Ablation, please see:
Before PRK or Surface Ablation