There are four types of laser vision correction procedures available using the Excimer laser: PRK (photorefractive keratectomy), LASIK, LASEK (laser epithelial keratomileusis) and Epi-LASIK (epithelial laser in situ keratomileusis):
Prior to the 1980s, physicians were making radial and arcuate incisions to reshape the surface of the cornea and treat myopia and astigmatism respectively. This is called radial keratotomy or RK. The goal of this procedure was to reduce or eliminate a lifetime of dependence on corrective lenses. Since these incisions were about 90% deep, the structural integrity of the cornea was compromised making it more prone to injury and more likely to cause fluctuations in vision due to instability.
Researchers found that the technologically advanced Excimer laser was extremely accurate. Its cool ultraviolet beam caused no thermal damage to the corneal tissue as compared to other lasers. The Excimer laser has achieved utmost precision so that it can remove tissue with up to 0.25 microns of accuracy. Laser vision correction also added predictability, stability, and safety to the surgical correction of Refractive Errors such as nearsightedness, farsightedness and astigmatism.
The first human eye ever treated with laser vision correction using PRK in the USA was in 1989 and this procedure was first approved by the FDA in 1995. In PRK, the epithelial surface layer of the cornea is gently removed using a brush. The Excimer laser reshapes the underlying superficial layer. The epithelial surface layer is then allowed to heal over by placing a contact lens for a few days.
There are two steps in how your vision is corrected with LASIK. The first step creates a corneal flap with the femtosecond laser which uses ultrashort pulses (one femtosecond is equal to 10-15 second) that cut the corneal tissue using a photodisruption process. This flap is folded back to allow for the second step, which involves the reshaping of the exposed inner corneal surface with the Excimer laser. The corneal flap is then returned in its original position where it adheres securely without the need for stitches. . Most patients recover and see better very quickly.
The IntraLase iFS femtosecond laser, which Dr Khouri uses, was the first laser to be FDA approved for creating a corneal flap during the LASIK procedure in 2002. Prior to the development of the femtosecond laser, the corneal flap was created by a surgical instrument called a microkeratome. The rate of flap complications associated with the microkeratome and dry eye symptoms is greatly reduced with the use of the Intralase iFS femtosecond laser. Since the flap created with the femtosecond laser is thinner than when a microkeratome is used, there is more corneal tissue available to treat so you could still be a candidate for this procedure if you have a larger refractive error. In addition, the laser created flap is a more precisely predictable flap than with the blade of a microkeratome giving a superior visual result.
LASEK combines some steps from both PRK and LASIK. With LASEK, a flap of the surface epithelial layer is loosened with a diluted alcohol solution and lifted prior to treatment of the underlying superficial layer with the Excimer laser. The flap is repositioned as with LASIK. A protective contact lens is then placed over the cornea to allow the surface epithelial layer to heal.
Epi-LASIK is another surface ablation procedure very similar to LASEK where the surface epithelial layer of the cornea is removed with a specially designed mechanical instrument called an epithelial separator to create a thin flap of corneal epithelium. No alcohol is needed to soften or loosen the epithelial cells. The Excimer laser is then used to reshape the cornea and a contact lens is placed to allow the corneal epithelium to heal.
Since LASIK is performed in a deeper layer under a protective flap of corneal tissue, healing is faster with minimal post-operative discomfort, and more rapid visual recovery as compared to PRK, LASEK and Epi-LASIK.
PRK, LASEK and Epi-LASIK, are considered surface ablation procedures. These procedures may result in a more predictable outcome with Custom Laser Vision Correction as compared to LASIK because the treated area is closer to the surface epithelial layer where the high order aberrations are measured using the wavefront analysis obtained with the iDesign Advanced WaveScan Studio System. These procedures can also be advantageous in patients with a tendency toward dry eye as compared to LASIK because a deeper flap is avoided. They are also advantageous for patients with thinner corneas since the created flap is much thinner than with LASIK. The amount of refractive error that can be treated is also greater than with LASIK. If you are a very physically active individual, the risk of traumatic flap dislocation is avoided with these procedures.