Lasik, an acronym for Laser-assisted, is a form of refractive laser eye surgery procedure performed by ophthalmologists intended for correcting vision. The procedure is usually a preferred alternative to photorefractive keratectomy, PRK, as it requires less time for full recovery, and the patient experiences less pain overall.
The Lasik Operation
The Lasik Operation is performed with the patient awake and mobile; however, the patient typically is given a mild sedative and anesthetic eye drops.
Lasik is performed in two steps. The initial step is to create a flap of corneal tissue. This process is achieved with a mechanical microkeratome using a metal blade, or a femtosecond laser microkeratome that creates a series of tiny closely arranged bubbles within the cornea. A hinge is left at one end of this flap. The flap is folded back, revealing the stroma, the middle section of the cornea.
The second step of the procedure is to use an excimer laser to remodel the corneal stroma. The laser vaporizes tissue in a finely controlled manner without damaging adjacent stroma by releasing the molecular bonds that hold the cells together. No burning with heat or actual cutting is required to ablate the tissue. The layers of tissue removed are tens of micrometers thick.
Currently manufactured excimer lasers use a computer system that tracks the patient's eye position up to 4,000 times per second, redirecting laser pulses for precise placement. After the laser has reshaped the cornea, the Lasik flap is repositioned over the treatment area by the surgeon. The flap remains in position by natural adhesion until healing is completed.
Performing the laser ablation in the deeper corneal stroma and under the Lasik flap fools the cornea into not knowing that it has had surgery. The wound response is muted, thus the patient is typically provided rapid visual recovery and virtually no pain.
Wavefront-guided Lasik
Wavefront-guided Lasik is a variation of Lasik surgery where, rather than apply a simple correction of focusing power to the cornea (as in traditional Lasik), an ophthalmologist applies a spatially varying correction, using a computer- controlled high-power UV laser guided by measurements from a wavefront sensor.
The goal is to achieve a more optically perfect eye, though the final result still depends on the physician's success at predicting changes which occur during healing.
Nor are wavefront aberrations the factor to degrade vision; especially in older patients, scattering from microscopic particles plays a major role. Hence, patients expecting so-called "super vision" from such procedures may be disappointed.
Surgeons claim patients are generally more satisfied with this technique than with previous methods, particularly regarding lowered incidence of "halos", the visual artifact caused by spherical aberration induced in the eye by earlier methods.
Although there have been a number of improvements in Lasik technology, a large body of conclusive evidence on the chances of long-term complications is not yet in place. Also, there is a small chance of complications, such as slipped flap, corneal infection, haziness, halo, or glare. The procedure is irreversible.
The incidence of macular hole has been estimated at 0.2% to 0.3%.
The incidence of retinal detachment has been estimated at 0.36%.
The incidence of choroidal neovascularization has been estimated at 0.33%.
The incidence of uveitis has been estimated at 0.18%.
Although the cornea usually is thinner after Lasik because of the removal of part of the stroma, refractive surgeons strive to maintain a minimum thickness in order to not structurally weaken the cornea.
Decreased atmospheric pressure at higher altitudes has not been shown to be extremely dangerous to the eyes of Lasik patients. However, some mountain climbers have experienced a myopic shift at extreme altitudes. Although there are no published reports documenting diving-related complications after Lasik, urban legends that describe eyes that have popped open during scuba diving still persist.
There are also concerns about possible Lasik-related problems with night vision, to the extent that some armed forces around the world advise aspiring air force and special forces personnel not to have the surgery.
