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LASIKLASIK, an acronymfor Laser-assisted In SituKeratomileusis, is a form of refractivelasereye surgeryprocedure performed by ophthalmologistsintended 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.
History of LASIKThe concept of LASIK surgery was made possible by Dr Jose Barraquer, who around 1970 developed the first microkeratome, used to cut thin flaps in the corneaand 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, keratomileusisand photorefractive keratectomy. It quickly became popular due to its improved precision and lower frequency of complications compared with those techniques.[1] In 1991, LASIK was performed for the first time both in Europe [1] and in the United States by a team of clinical investigators including Stephen Slade, M.D., Robert Maloney, M.D [2]., George Waring, M.D., Marc Michelson, M.D [3], and Stephen Brint, M.D. [4] who began gathering data on the safety and efficacy of LASIK for the United States food and Drug Administration. [2]. The same year, the Drs. Thomas and Tobias Neuhann successfully treated the first German LASIK patients with an automated microkeratome. Surgical procedurePre-operativePatients wearing contact lenses are typically instructed to stop wearing them approximately 7 to 10 days prior to surgery. Prior to the surgery, the surfaces of the patient's corneasare examined with a computer-controlled scanning device to determine their exact shape. Using low-power lasers, it creates a topographic mapof the cornea. This process also detects astigmatismand 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 is typically prescribed an antibiotic to start taking beforehand, to minimize the risk of infection after the procedure. The operationThe operation is performed with the patient awake and functional; however, the patient is typically 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 femtosecondlaser. 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 vaporizestissue without causing damage to adjacent stroma in a finely-controlled manner. The layers of tissue removed are tens of micrometreswide. ComplicationsImage:Eye hemorrhage.jpg Although relatively uncommon, complications due to LASIK do occur. The following are some of the more frequently reported complications of LASIK [3]:
Flap complications (such as displaced flaps or folds in the flaps that requiring repositioning, diffuse lamellar keratitis, and epithelial ingrowth) are relatively common in lamellar corneal surgeries [4], but rarely lead to permanent visual acuity loss; the incidence of these microkeratome-related complications decreases with increased physician experience [5] [6]. A slipped flap (when the corneal flap detaches from the rest of the cornea) is one of the most common complications. The chances of this are greatest immediately following surgery, so patients are typically recommended to go home and sleep, to let the flap heal. Halos or starbursts around bright lights at night are caused by the irregularity between the lasered part and the untouched. It is not practical to perform the surgery so it covers the width of the pupil at full dilation at night, so the pupil may expand so that light passes through the edge of the surgery into the pupil. In daytime, the pupil is smaller than the edge. Newer equipment is available to properly deal with those with large pupils, and responsible physicians will check for this during examination. Although LASIK technology is improving at a rapid pace, 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. Infectionunder the corneal flap is possible. It is also possible that the patient has a genetic condition that causes the cornea to thin out following surgery. While this is screened for in the pre-op 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 require a corneal transplant. Although the cornea is usually thinner after LASIK due to 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 climbershave experienced a myopic shift at extreme altitudes [7][8]. Although there are no published reports documenting diving related complications after LASIK [9], urban legendsthat describe eyes that have popped open while scuba divingstill persist. There are also concerns for possible LASIK-related problems with night vision, to the exent that some armed forces around the world recommend to aspiring air forces and special forces personnel to not take the surgery. Factors affecting the surgeryThe cornea is typically avascular in that it must be transparent to function normally. Its cells absorb oxygenfrom 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 due to 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 is discontinued several days to weeks prior to the LASIK procedure. A 2004Wake Forest Universitystudy found that Lasik results are affected by heat and humidity, both during the procedure and in the two weeks preceding surgery[10]. Safety and efficacyThe reported figures for safety and efficacy are widely open to interpretation. In 2003, the Medical Defence Union, the largest insurer for doctors in the United Kingdom, reported a 166% increase in claims involving laser eye surgery, however, the MDU pointed out that these claims were primarily due to patients' ?unrealistic expectations? of LASIK rather than ?faulty surgery? [11]. A 2003 study reported in the medical journal Ophthalmology found that nearly 18% of treated patients, and 12% of treated eyes, required retreatments [12]. 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 Clinical Excellenceconsidered a systematic reviewof four randomised controlled trials [13][14]prior to issuing guidance for the use of LASIK within the NHS[15]. Regarding the procedure's efficacy, NICE reported that "[c]urrent 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 "[e]vidence 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[16][17]. See also
External links
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