PRK and epi-LASEK
PRK, or photorefractive keratectomy is a laser technique that treats the middle layers of the cornea to correct hyperopia (farsightedness), myopia (nearsightedness) and astigmatism. The purpose of PRK is to reshape the cornea to help the eye to focus at far distances, reducing, or in some cases eliminating, the need for glasses or contact lenses.
PRK is performed using topical anesthetic (eye drops that eliminate pain). Next, a small spring-like device is inserted to help keep the eye open. Using a small hand instrument, the front surface cells of the cornea are gently removed. This allows access to the layers of the cornea that need to be treated by the laser.
The laser procedure is then performed on the cornea. It is this "lasering" that shapes the cornea for improved vision. The laser treatment lasts 30 to 90 seconds. Afterwards, a contact lens is placed over the front surface of the cornea. This contact lens acts as a bandage to help the cornea heal its front surface.
The entire procedure takes about 5 minutes to complete. Patients are typically amazed at the comfort and speed of the procedure. Since the eye is completely anesthetized, patients do not feel the instruments or the laser. However, some pressure may be felt by a small spring device, which is used to help keep the eyelids open.
Patients are placed on antibiotic and anti-inflammatory eye drops to promote comfort, prevent infection, and reduce inflammation. These drops are used four times a day initially and tapered over a few days to a week. Follow-up examinations are scheduled daily until the front surface of the eye heals (usually two to four days), then at one week, one month, and three months postoperatively.
LASIK vs. PRK:
As with any surgical procedure, complications can occur. Fortunately, the majority of PRK complications are easily treated and have little effect on final visual outcome. Postoperative complications in the short term can be associated with infections or inflammation. These can usually be treated with antibiotics or steroids. Sometimes haze or shifts in refraction may require the use of steroids. Fortunately, most haze disappears, and shifts generally stabilize.
There are minimal restrictions on activities following PRK. Exercise, watching TV, reading, flying, and driving are all acceptable, as long as the patient feels up to it. The major activity to be avoided is eye rubbing, which could possibly dislodge the contact lens. Additionally, driving or operating heavy machinery should be avoided for a day or two if sedatives (such as Valium) are used during the operation.
epi-LASEK, or laser epithelial keratomileusis, (not a misspelling of LASIK) is simply a modified PRK procedure. It is not to be confused with LASIK which, of course, is the application of the same excimer laser to the mid-cornea following the creation of a corneal flap with a surgical instrument known as the microkeratome.
The epi-LASEK procedure is almost identical to the PRK procedure, but varies in the following way. Once the eye is anesthetized with powerful numbing drops, a few drops of a very dilute alcohol solution are applied to a central circumscribed area on the surface of the cornea and allowed to stay in contact with the corneal surface for about 20 - 30 seconds. This weak alcohol solution is then rinsed off the surface of the eye. The function of the weak alcohol solution is to loosen the epithelial layer (50 microns) and to allow it to be peeled back in a sheet of epithelial cells, thereby exposing the underlying Bowman's layer. This is not to be confused with LASIK, which actually uses a microkeratome instrument to create a flap of both epithelium and the front part of the stromal tissue measuring anywhere between 130 to 180 microns. In epi-LASEK, the epithelium-only layer is laid back in a similar fashion to LASIK, but consists of only epithelium, not corneal stroma. In epi-LASEK, once the epithelial cells have been laid out of the way, the laser is applied to Bowman's layer in the exact same fashion as in PRK. Once the laser treatment has been completed, the epithelial layer is laid back into place and a soft contact lens is placed over the eye as in PRK.
Essentially, epi-LASEK and PRK are identical, except for the fact that following the application of the laser in epi-LASEK, the epithelial cells which have been partly devitalized by the weak alcohol solution are laid back over the treatment area and may serve to facilitate healing of new epithelium.
Sometimes when epi-LASEK is attempted, the ultra-thin epithelium-only flap is not strong enough to be laid back over the treatment zone. In these cases, the epithelium will be simply wiped away as it would have been in the PRK procedure. Thus, in this situation, the epi-LASEK becomes a PRK. If this happens it is not a cause for concern in that it will not adversely affect the visual result. Even if we plan and attempt epi-LASEK we cannot guarantee that the epi-LASEK will be completed - the epithelium of each individual behaves differently.
Although similar in the acronym spelling, epi-LASEK and LASIK are not similar procedures. Epi-LASEK and PRK are similar, the only difference is that in PRK, the epithelium is removed completely whereas in epi-LASEK the patient's epithelium serves as its own bandage following the procedure.
The visual results of epi-LASEK and PRK are essentially the same, as are the side effects, risks, and complications.
It is likely that epi-LASEK will become increasingly popular for patients who must undergo PRK. epi-LASEK will not replace LASIK.
Why should a patient have epi-LASEK versus PRK? Probably the only reasons are slightly increased comfort following the procedure (although, in our hands, PRK patients have not complained of discomfort in the post-operative period), and possibly it may aid in the rapidity of the healing of the epithelium.
Although PRK has fallen out of favor over the past few years because LASIK is so much more convenient for the patient in the early post-operative period, PRK is gaining in popularity now with the advent of the larger optical zone lasers capable of performing laser treatments in patients with pupils up to 9mm. Because the depth of the treatment into the cornea increases as the treatment diameter increases, patients with large pupils and thin corneas who desire refractive surgery may have no choice other than to have PRK or epi-LASEK rather than LASIK, because in LASIK, the corneal thickness required to accommodate larger and deeper treatment zones may not be sufficient in patients with large pupils.
In summary, PRK and epi-LASEK provide an excellent means to reduce farsightedness, nearsightedness and astigmatism.