Excimer lasers are gas lasers that emit powerful ultraviolet pulses lasting from a few to hundreds of nanoseconds. The usual active medium is a gas mixture containing a rare gas and a halogen, which are combined to form a short-lived rare-gas halide molecule. Clinical excimer lasers use argon and fluorine gases to generate ultraviolet light with a wavelength of 193 nm. The energy from this wavelength of light is high enough to break the molecular bonds in the cornea and remove tissue. The ablation results in submicron tissue removal with every laser pulse, with minimal to no damage to the remaining tissue.

Although LASIK offers almost immediate visual correction, improved comfort and stability, and minimum wound healing complications compared to photorefractive keratectomy (PRK), it requires far more surgical skill, as it involves the use of both sophisticated and complicated microkeratome technology.

The technician and the surgeon should check the laser and the microkeratome before surgery. The surgeon should also confirm that the correct treatment data are entered
into the laser computer. Both the surgeon and the technician should verify the patient’s name, the pupil diameter (in scotopic conditions), the thickness of the central cornea, and the attempted correction.

An eyelid speculum is inserted in the operative eye, which has been anesthetized topically, and the fellow eye is covered. The cornea is marked with an instrument that can allow postoperative proper flap alignment. A suction ring is placed on the eye to achieve an adequate IOP for the creation of the cornea flap. There are several indications that suction is adequate for flap creation, such as pupil dilatation, contact applanation device, or the patient’s decreased vision. Corneal lamellar dissection has a steep learning curve, with the potential for severe, vision-threatening complications. Newer microkeratomes have improved the safety and reliability of the procedure. After flap creation (some microkeratomes give surgeons the ability to choose the hinge position—superior, nasal, or oblique), the residual corneal bed stroma is examined for irregularities. The next steps include flap protection, intraoperative pachymetry, centration and ablation; all these steps should be done as quickly as possible to minimize the time of exposure of the stromal surface (avoiding stromal dehydration, which eventually leads to overcorrection and, in very rare conditions, to corneal perforation).

Centration of the laser beam is also crucial for a successful operation. For myopic eyes, the ablation beam is centered on the center of the pupil. It is centered slightly nasal to the corneal light reflex for hyperopic corrections.

The tracking system is activated during the beam centration. Small saccadic eye movements are acceptable, but the surgeon must stop the ablation if the eye starts drifting away from the fixation target. Once the ablation is completed, the corneal stromal bed is cleaned with a dry sponge. The flap is replaced onto the bed using a bent cannula while irrigation of the interface with balanced salt solution is performed to remove any remaining debris. This also facilitates the floating of the flap back into its original position. Aggressive irrigation should be avoided because it leads to flap edema, which increases the incidence of epithelial ingrowth (presence of an area of poor flap adherence). For proper flap alignment, the corneal marks should be properly aligned.

The majority of LASIK patients require minimum postoperative follow-up and have excellent refractive results, even in the presence of minor flap complications. Severely complicated cases, however, require intensive monitoring of the eye’s status.

The main goals of postoperative management include the proper flap alignment to the stromal bed, the recognition and management of complications, and the modulation of refractive status. LASIK patients are typically examined 1 to 2 hours after the operation (to ensure that the flap is properly aligned), on the first postoperative day (if striae or other flap irregularities are evident, the flap should be lifted back and repositioned), and at 1, 3, 6, and 12 months postoperatively.

The postoperative regimen varies significantly between refractive surgeons, but in general it includes a topical combined antibiotic-steroid agent tapered for 15 days to prevent infection and control inflammation.

The widespread growth of LASIK has not resulted in notably serious complications. The few that have occurred, however, are of great importance when considering the elective nature of such a procedure and the ever-growing number of available alternatives (6, 7, 8). Among the many classifications of LASIK complications, the most popular is the one that lists complications in chronological order.