LASIK, or laser assisted in situ keratomileusis, is a laser surgical technique that treats the middle layers of the cornea to correct hyperopia (farsightedness), myopia (nearsightedness) and astigmatism. The purpose of LASIK 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.
While LASIK and PRK, or photorefractive keratectomy both use the excimer laser to provide the eye’s correction, LASIK generally is preferable with regard to the speed and comfort of visual recovery. However, we believe that the final outcome of LASIK and PRK is similar for low to moderate myopia (defined as less than –6 diopters of correction).
LASIK, like PRK, is performed using topical anesthetic (eye drops that eliminate pain). A vacuum ring secures the eye while a thin (160-micron) 9-mm circular layer of the cornea is formed into a flap. This is done with a device called a microkeratome, which is a specialized scalpel that creates the corneal flap. Although the microkeratome uses a knife to make an incision, this incision does nothing to change the corneal shape (as opposed to radial keratotomy, or RK, which uses a knife to reshape the cornea). If, for example, the flap were returned to its normal anatomical position WITHOUT any laser resurfacing, one would still require the original prescription for glasses or contacts. The corneal flap remains connected to the eye and is folded to one side.
The laser procedure is then performed in the bed of the cornea that was created with the microkeratome. It is this “lasering” that shapes the cornea for improved vision. The laser treatment lasts 30 to 90 seconds. Afterwards, the flap is returned to its original position. The cornea creates a natural “suction” that holds the flap in place without the need for stitches or glue. Once the LASIK is completed, the eye is observed for 2 to 3 minutes to ensure the corneal flap has completely re-adhered. At this point, the patient can blink normally, and the surgeon tests the flap to make sure that it is secure. The eye is then covered overnight with a clear plastic protective eye shield; this protects against inadvertent eye rubbing and allows the edges of the flap to cover with epithelium (the skin of the eye), which normally takes a few hours.
The entire procedure takes approximately 10 minutes to complete. The procedure is somewhat longer than for PRK, because the surgeon needs to be absolutely meticulous about the creation of the flap and the placement of the flap after lasering. Patients are typically amazed at the comfort and speed at which this procedure is done. Since the eye is completely anesthetized, patients do not feel the microkeratome or the laser. However, some pressure may be felt by a small spring device, which is used to help keep the eyelids open, and by the suction device used to guide the microkeratome.
While it is possible to dislodge the corneal flap during the first day or two by physically rubbing the eye, patients are fit with a clear plastic eye shield to prevent any eye trauma that could disturb the eye. This eye shield is worn through the first postoperative day, and then nightly for the next four evenings.
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. Follow-up examinations are scheduled at one day, one week, one month, and three months postoperatively.
LASIK vs. PRK:
- There is typically mild discomfort in the first 1-2 days after LASIK, whereas PRK may produce more discomfort or, in some instances, significant discomfort. Since none of the surface tissues of the eye are removed in LASIK (as opposed to PRK), the eye remains protected by its natural epithelial barrier. The only time it is not covered is when the flap is folded over for the laser procedure, and when the thin edge of the flap is healing, which normally takes a few hours after the laser procedure. In general, no contact lens is necessary for LASIK healing. PRK, on the other hand, requires that the surface cells (epithelium) be physically scraped off before the laser procedure is done. After the excimer laser is used, the eye is fit with a bandage contact lens (like an eye “Band-Aid” TM), and the epithelium regenerates. This takes two to four days, depending on the eye’s healing powers. The epithelial healing process can range from mild discomfort to overt pain. Usually, the patient feels like he/she scratched her eye putting a contact lens in. While topical (eye drop) medication can be used to decrease the pain sensation, sometimes strong oral pain medications are necessary.
- Typically, visual recovery is exceedingly quick for LASIK, generally within a few days. Again, this is due to the fact that the eye’s natural coverings are returned to their original locations. Visual recovery for PRK, on the other hand, can take from 1-2 weeks to months, depending on the amount of correction performed. For both procedures, the final visual results are due to the effects of the laser procedure itself and the patient’s own healing patterns.
- Since no two patients heal exactly alike, some variability in the final visual outcomes can be expected, and sometimes retreatments (requiring further lasering) are necessary. For retreatments with PRK, the surface cells have to be rescraped, with the associated post lasering healing discomfort for two to four more days. With LASIK retreatments, on the other hand, the ORIGINAL flap can be lifted and replaced with minimal patient discomfort.
- When treating greater degrees of myopia with PRK, more patient healing is required, and there is more variability in results and more risk of abnormal healing in the form of surface haze (a form of eye scarring that occurs with PRK). The inner layers of the cornea are far less likely to react and rarely produce haze or scar tissue, making LASIK a more ideal procedure for treating higher myopia.
- LASIK introduces the risks of complications produced by the microkeratome; these risks are obviously not found with PRK.
As with any surgical procedure, complications can occur. Fortunately, the majority of LASIK complications are easily treated and have little effect on final visual outcome. Intraoperative complications associated with the creation of the flap are the most frequent. A flap may be partially created (partial flap), or may be cut loose from the cornea (free cap). Sometimes, with the creation of a free cap, the laser procedure can still be performed. If either of these complications occur, the flap or cap is repositioned on the cornea, and the LASIK procedure can be repeated in approximately three months if necessary. Other intraoperative complications include inadvertent perforation of the eye. Fortunately, with meticulous surgical technique, this complication is extremely rare.
Postoperative complications in the short term can be associated with infections or inflammation. These can usually be treated with antibiotics or steroids. Occasionally, epithelial cells can grow under the flap. These cells may have to physically be removed.
There are minimal restrictions on activities following LASIK. Exercise, watching TV, reading, flying, and driving are all acceptable. The major activity to be avoided is eye rubbing, which could possibly dislodge the flap. Additionally, driving or operating heavy machinery should be avoided for a day or two if sedatives (such as Valium) are used during the operation
In summary, LASIK provides an excellent means to reduce farsightedness, nearsightedness and astigmatism. Furthermore, patient comfort and visual recovery are generally quicker than with PRK, while providing the precision and stability of excimer laser correction.