LASIK, an acronym for Laser-Assisted In Situ Keratomileusis, is a refractive surgery procedure intended for correcting the vision in order to reduce a person's dependency on corrective devices, such as glasses or contact lenses. The procedure is usually a preferred alternative to PRK, or photorefractive keratectomy, as it requires less time for full recovery, and the patient experiences less pain overall.
The first step in the procedure consists of mapping the corneal surface with a computer controlled scanning device to determine the exact shape. Then the appropriate amount of tissue which needs to be removed is calculated, such that upon replacing the flap there is no need (or less need) for corrective devices like spectacles and lenses. A computer system tracks the patient's eye position 4,000 times per second, redirecting laser pulses for precise placement.
Then an excimer laser (193 nm) is used to remodel the corneal stroma after lifting a partial thickness corneal flap made by a microkeratome or femtosecond laser. Excimer laser ablates tissue without causing damage to adjacent stroma in a finely controlled manner.
The technology is improving at a rapid pace, but 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, amongst others. The procedure is irreversible.
A 2004 Wake Forest University study found that Lasik results are affected by heat and humidity, both during the procedure and in the two weeks preceding surgery[1].
The NHS National Institute for Clinical Excellence's December 2004 guidance on laser eye surgery [2] found that evidence is weak for its effectiveness in treating severe short- or long-sightedness (only 26-36% had an uncorrected visual acuity of 20/20 or so); that 5% of cases had complications; and notes concerns about long-term safety of thinning the cornea.
Public information from the official LASIK FDA site:
"LASIK is a procedure that permanently changes the shape of the cornea, the clear covering of the front of the eye, using an excimer laser. A knife, called a microkeratome, is used to cut a flap in 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. Pulses from a computer-controlled laser vaporize a portion of the stroma and the flap is replaced."
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