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LASIK stands for Laser In-Situ Keratomileusis, which translates: "using a laser to reshape the cornea from the inside." It was first performed in 1991.

The basic elements of the LASIK procedure involves the creation of a flap in the outer cornea; moving the flap to the side to expose the inner part of the cornea; using an excimer laser to reshape the cornea based on the patient's specific measurements, and then replacing the flap to its original position. The reshaped cornea then focuses the previously unfocused light rays onto the retina.

At a more detailed level, LASIK is in fact two procedures combined:

Microkeratome (Flapmaker)

The first procedure, keratomileusis, which was developed in the late 1950s, employs a small surgical instrument: a microkeratome (much like a carpenter's plane) that creates smooth flaps with a mechanically oscillating tiny blade contained within a microkeratome metal head. The head is used in conjunction with a suction ring that holds the eye in position during the flap creation. (Back then, lasers were not developed for reshaping the cornea. To do so, the microkeratome was used a second time under the flap.) The same principles underlying the original microkeratomes are used in the modern microkeratomes. The long-term safety record of properly created flaps in the cornea is excellent, and many microkeratomes are currently FDA approved.

Excimer Laser

The excimer laser was developed in the 1980s for reshaping the eye. The precision wavelength of 193 nanometers was found to be the safest and most accurate. Many excimer lasers are FDA approved, but not all lasers have the same range of approvals. For example, one brand of laser may be FDA approved only for treating myopia without astigmatism, while another laser may be FDA approved for all five possible conditions: myopia with and without astigmatism, hyperopia with and without astigmatism, and mixed astigmatism.

The most advanced lasers today are small spot (less than 2 mm) and have advanced eye-tracker technology that follows the eye during the laser application (this compensates for small eye movements). Such lasers have adjustable treatment zones up to 8.0 mm to compensate for large pupil diameters. Lasers have extremely sophisticated self-run computer diagnostics that verify this entire system during calibration testing. The most advanced lasers available today can correct myopia with/without astigmatism and hyperopia with/without astigmatism.

Brief History of Refractive Surgery

LASIK was developed from procedures described above. The excimer laser was initially developed to aid in a procedure called radial keratotomy (RK). In the early 1980s, RK involved changing the corneal shape for myopia by making tiny slits in the outer cornea with a special blade. The excimer laser was created in an attempt to replace the blade for RK surgery. Shortly afterwards the excimer laser was used instead to directly reshape the central cornea in a procedure called photorefractive keratectomy (PRK).