LASIK, an acronym for Laser-assisted In Situ Keratomileusis, 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 technique was made possible by Dr Jose Barraquer, who around 1970 developed the first microkeratome, used to cut thin flaps in the cornea and alter its shape, in a procedure called keratomileusis.

LASIK surgery was developed in 1990 by Dr. Lucio Buratto (Italy) and Dr. Ioannis Pallikaris (Greece) as a melding of two prior techniques, keratomileusis and photorefractive keratectomy. It quickly became popular because of its greater precision and lower frequency of complications compared with those techniques.[1]

In 1991, LASIK was performed for the first time in the United States by Drs. Stephen Brint and Stephen Slade [2]. The same year, Drs. Thomas and Tobias Neuhann successfully treated the first German LASIK patients with an automated microkeratome.

Patients wearing soft contact lenses typically are instructed to stop wearing them approximately 7 to 10 days before surgery. Patients wearing hard contact lenses should stop wearing them for a minimum of six weeks plus another six weeks for every three years the hard contacts had been worn. [3] Before the surgery, the surfaces of the patient's corneas are examined with a computer-controlled scanning device to determine their exact shape. Using low-power lasers, it creates a topographic map of the cornea. This process also detects astigmatism and other irregularities in the shape of the cornea. Using this information, the surgeon calculates the amount and locations of corneal tissue to be removed during the operation. The patient typically is prescribed an antibiotic to start taking beforehand, to minimize the risk of infection after the procedure.

The operation is performed with the patient awake and mobile; however, the patient typically is given a mild sedative (such as Valium or diazepam) and anesthetic eye drops. The surgeon operates the lasers, which make all of the incisions. A computer system tracks the patient's eye position 4,000 times per second, redirecting laser pulses for precise placement. A flap is cut in the cornea using a blade (called a microkeratome) or a femtosecond laser. A hinge is left at one end of this flap. The flap is folded back, revealing the stroma, the middle section of the cornea.

Then an excimer laser (193 nm) is used to remodel the corneal stroma. The laser vaporizes tissue in a finely controlled manner, without damaging adjacent stroma. The layers of tissue removed are tens of micrometers wide.

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. However, 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.

The incidence of refractive surgery patients having unresolved complications six months after surgery has been estimated from 3%^[1] to 6%^[2]. The following are some of the more frequently reported complications of LASIK^[1][4]:

• Dry eyes
• Overcorrection or undercorrection
• Visual acuity fluctuation
• Halos or starbursts around light sources at night
• Light sensitivity
• Ghosts or double vision
• Wrinkles in flap (striae)
• Decentered ablation
• Debris or growth under flap
• Thin or buttonhole flap
• Induced astigmatism
• Epithelium erosion
• Posterior vitreous detachment^[3]
• Macular hole^[4]

Complications due to LASIK have been classified as those that occur due to preoperative, intraoperative, early postoperative, or late postoperative sources^[5]:

The incidence of flap complications has been estimated to be 0.244%^[6]. Flap complications (such as displaced flaps or folds in the flaps that necessitate repositioning, diffuse lamellar keratitis, and epithelial ingrowth) are common in lamellar corneal surgeries [5] but rarely lead to permanent visual acuity loss; the incidence of these microkeratome-related complications decreases with increased physician experience [6] [7].

A slipped flap (a corneal flap that detaches from the rest of the cornea) is one of the most common complications. The chances of this are greatest immediately after surgery, so patients typically are advised to go home and sleep, to let the flap heal.

Flap interface particles are another finding whose clinical significance is undetermined^[7]. A Finnish study found that particles of various sizes and reflectivity were clinically visible in 38.7% of eyes examined via slit lamp biomicroscopy, but apparent in 100% of eyes using confocal microscopy^[7].

The incidence of diffuse lamellar keratits, also known as the Sands of Sahara syndrome, has been estimated at 2.3%^[8].

The incidence of infection responsive to treatment has been estimated at 0.4%^[8]. Infection under the corneal flap is possible. It is also possible that a patient has a genetic condition that causes the cornea to thin out after surgery. Although this condition is screened for in the preoperative exam, it is possible in rare cases (about 1 in 5,000) for the condition to remain dormant until later in life (the mid-40s). If this occurs, the patient will need a corneal transplant.

The incidence of persistent dry eye has been estimated to be as high as 28% in Asian eyes and 5% in Caucasian eyes^[2]. Nerve fibers in the cornea are important for stimulating tear production. A year after LASIK subbasal nerve fiber bundles remain reduced by more than half ^[9].

The incidence of subconjunctival hemorrhage has been estimated at 10.5%^[8].

The incidence of epithelial ingrowth has been estimated at 0.1%^[8].

Glare is another commonly reportedly complication of those who have had LASIK^[10]. Halos or starbursts around bright lights at night are caused by the irregularity between the lasered part and the untouched part. It is not practical to perform the surgery so that it covers the width of the pupil at full dilation at night, and the pupil may expand so that light passes through the edge of the flap into the pupil. In daytime, the pupil is smaller than the edge. Newer equipment is available to properly treat those with large pupils, and responsible physicians will check for them during examination.

Although there have been a number improvements in LASIK technology [8][9] [10] , 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%^[4] to 0.3% ^[11].

The incidence of retinal detachment has been estimated at 0.36%^[11].

The incidence of choroidal neovascularization has been estimated at 0.33%^[11].

The incidence of uveitis has been estimated at 0.18%^[12]

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 [11] [12]. Although there are no published reports documenting diving-related complications after LASIK [13], 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 exent that some armed forces around the world advise aspiring air force and special forces personnel not to have the surgery.

Laser in situ keratomileusis increases higher order wavefront aberrations of the cornea^{[13] [14]}. Glasses do not correct higher order aberrations.

Microfolding has been reported as "an almost unavoidable complication of LASIK" whose "clinical significance appears negligible" ^[7].

The cornea typically is avascular because it must be transparent to function normally. Its cells absorb oxygen from the tear film. Low oxygen-permeable contact lenses reduce the cornea's absorption of oxygen, which sometimes results in the growth of blood vessels into the cornea, a process known as corneal neovascularization. This can cause a mild increase in inflammation and healing time and some discomfort during the surgery because of augmented bleeding. Although some contact lenses, notably modern RGP and soft silicone hydrogel lenses, are made of materials with higher oxygen permeability that help reduce the risk of corneal neovascularization, patients considering LASIK are cautioned to avoid overwearing their lenses. It is usually recommended that contact lens use be discontinued several days or weeks before the LASIK procedure.

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 before surgery[14].

Various surveys have been performed to determine patient satisfaction with LASIK:

• According to a 2005 survey, 92.2% of patients reported that they were satisfied or very satisfied with their surgery^[10].
• According to a 2004 survey, 97.8% declared themselves as satisfied^[15].
• According to a 2003 survey, 97% of subjects returning a questionnaire reported that they would recommend LASIK to a friend. The study found that those who would not recommend the procedure were more likely to have experienced glare, halos, and/or starbursts^[16].
• According to a 2000 survey, 97.9% of patients reported that they were satisfied^[17].

The reported figures for safety and efficacy are open to interpretation. In 2003, the Medical Defence Union (MDU), the largest insurer for doctors in the United Kingdom, reported a 166% increase in claims involving laser eye surgery; however, the MDU averred that these claims resulted primarily from patients' “unrealistic expectations” of LASIK rather than “faulty surgery” [15]. A 2003 study reported in the medical journal Ophthalmology found that nearly 18% of treated patients and 12% of treated eyes needed retreatment [16]. The authors concluded that “higher initial corrections, astigmatism, and older age are risk factors for LASIK retreatment.”

In 2004, the British National Health Service's National Institute for Health and Clinical Excellence (NICE) considered a systematic review of four randomized controlled trials [17] [18] before issuing guidance for the use of LASIK within the NHS[19]. Regarding the procedure's efficacy, NICE reported, "Current evidence on LASIK for the treatment of refractive errors suggests that it is effective in selected patients with mild or moderate short-sightedness" but that "evidence is weaker for its effectiveness in severe short-sightedness and long-sightedness." Regarding the procedure's safety, NICE reported that "there are concerns about the procedure's safety in the long term and current evidence does not appear adequate to support its use within the NHS without special arrangements for consent and for audit or research." Leading refractive surgeons in the United Kingdom and United States, including at least one author of a study cited in the report, believe NICE relied on information that is severely dated and weakly researched[20] [21].

• LASEK (Laser-Assisted Sub-Epithelial Keratectomy) or PRK (Photorefractive keratectomy)
• Radial keratotomy
• Wavefront

• FDA information page on LASIK
• LasikDisaster: Anti-LASIK site hosting patients' accounts of bad surgical outcomes
• LASIKsucks4U: LASIK website hosting patients' account of bad surgical outcomes, studies relating to the LASIK industry, and much more
• Clario: Refractive corneal surgery database and lexicon
• Visionsimulations.com: How patients with refractive surgery complications see the world.
• SurgicalEyes: Support site for people with complications from LASIK and other eye surgeries.
• Cooking For Engineers: LASIK - Michael Chu describes in detail his LASIK experience and includes simulated diagrams and photos to show his vision post-operation
• Council for Refractive Surgery Quality Assurance - Lasik Patient Advocacy
• Vision Surgery Rehab Network: Support site for people with complications from LASIK and other eye surgeries.