Surface Ablation (PRK and Epi-LASIK) Versus LASIK
By Dr. Christopher J. Rapuano
Published on October 12, 2007
Excimer laser refractive surgery involves using an excimer laser to reshape the cornea to decrease, or ideally eliminate, nearsightedness, farsightedness, and/or astigmatism. The excimer laser can be applied to the surface of the cornea (surface ablation) or to the middle of the cornea, after creating and lifting a corneal flap (LASIK or laser in situ keratomileusis).
PRK (photorefractive keratectomy) involves wiping off the surface layer of the cornea (epithelium) to create a “corneal abrasion.” The laser treatment is then applied to the underlying tissue to reshape the cornea. Epi-LASIK is a new variant of PRK, where the epithelial layer is removed with a blunt vibrating blade attached to a suction ring. The potential advantage of the Epi-LASIK procedure over PRK is the “abrasion” tends to be a little smaller and more regular and heals a little faster.
The advantages of surface ablation include the fact that it has been around since the early 1990s, gets excellent results, and does not weaken the cornea significantly. Additionally, there is no corneal flap to worry about; that is, there are no problems creating a flap and no problems with the healing of a flap.
The disadvantages of surface ablation are related to the “abrasion.” It causes discomfort or pain until it heals, which typically takes 2-3 days. Vision is poor for several days until the abrasion heals. Vision is generally good at one week, very good at two weeks, but may take 4-6 weeks to be excellent. Additionally, there is often some corneal “haze” related to the healing process. While the haze is usually mild and does not affect vision, it can significantly affect vision in rare cases. Steroid drops are generally used for several months after surface ablation to help decrease the chance of haze. Occasionally, a drop called mitomycin C is placed on the cornea for 10-60 seconds immediately after the laser treatment to decrease the chance of haze.
LASIK involves creating a corneal flap, moving it to the side, using the excimer laser to reshape the underlying cornea, and replacing the flap. To create the flap, a suction ring is placed on the eye, the eye is pressurized, and a sharp vibrating blade or femtosecond laser is used to create the flap, which is about 1/4 of the thickness of the cornea. The flap is created with a hinge so it can be easily repositioned.
The advantages of LASIK include minimal discomfort, rapid visual recovery, and little to no central corneal haze. Patients typically experience grittiness and tearing for about 4-6 hours after LASIK, but the eyes generally feel back to normal by the next day. Recovery of vision depends on numerous factors, including the strength of the prescription being treated. However, vision the day after LASIK is generally very good and becomes excellent over the next few days to a week or two. There is a very low chance of haze in the central cornea and consequently, steroid drops are usually used for one week or less after surgery.
The disadvantages of LASIK primarily revolve around the creation and healing of the flap. Whether the flap is fashioned with a motorized blade (microkeratome) or laser (femtosecond laser), there are rarely problems in flap creation. The flap can be off center, too small, too thin, too thick, have a hole in it (buttonhole) or have no hinge (free cap). Even if the flap is created perfectly, it may need to be repositioned to sit perfectly. Soon after surgery, simply rubbing the eye can displace the flap. Months and even years after surgery, trauma to the eye can displace the flap. Flap displacement causes pain and decreased vision and, while it can be treated, it increases the risk of other problems. Complications can also develop in the space under the flap including inflammation (DLK or diffuse lamellar keratitis) and infection, which is difficult to treat. Epithelial cells from the corneal surface can also grow under the flap (epithelial ingrowth) and cause visual problems and damage to the flap. Creation of the LASIK flap also weakens the cornea somewhat, which increases the risk of progressive corneal thinning and irregularity (ectasia), which can cause a significant decrease in vision. Patients with thin corneas, very strong prescriptions, and irregular corneal curvatures before surgery are at higher risk of this complication. In appropriate patients, complications of LASIK are rare.
Surface ablation and LASIK are excellent procedures, both in terms of safety and efficacy. However, some patients may be better candidates for one rather than the other. You should discuss your specific examination results and your expectations with your surgeon before deciding which procedure is best for you.