LASIK is the acronym for Laser-Assisted in Situ Keratomileusis, a type of refractive laser eye surgery performed by ophthalmologists for correcting myopia, hyperopia, and astigmatism.^[1] The procedure is generally preferred to photorefractive keratectomy, PRK, (also called ASA, Advanced Surface Ablation) because it requires less time for the patient's recovery, and the patient feels less pain, overall; however, there are instances where PRK/ASA is medically indicated as a better alternative to LASIK. Many patients choose LASIK as an alternative to wearing corrective eyeglasses or contact lenses. It has been suggested that this article or section be merged with Backronym and Apronym (Discuss) Acronyms and initialisms are abbreviations, such as NATO, laser, and ABC, written as the initial letter or letters of words, and pronounced on the basis of this abbreviated written form. ... For other uses, see Laser (disambiguation). ... In situ is a Latin phrase meaning in the place. ... Keratomileusis is the surgical improvement of the refractive state of the cornea performed by lifting up the front surface of the eye by forming a thin hinged flap under which the shape of the cornea is changed by using an excimer laser or other surgical device. ... Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease dependency on glasses or contact lenses. ... For other uses, see Laser (disambiguation). ... Eye surgery in the middle ages. ... Ophthalmology is the branch of medicine which deals with the diseases of the eye and their treatment. ... Normal vision. ... Hyperopia, also known as hypermetropia or colloquially as farsightedness or longsightedness, is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short or when the lens cannot become round enough), causing inability to focus on near objects, and in extreme cases causing... Astigmatism is an affliction of the eye, where vision is blurred by an irregularly shaped cornea. ... // Photorefractive keratectomy (PRK) and Laser-Assisted Sub-Epithelial Keratectomy (LASEK) are laser eye surgery procedures intended to correct a persons vision and reduce their dependency on glasses or contact lenses. ... Glasses, spectacles, or eyeglasses are frames bearing lenses worn in front of the eyes, sometimes for purely aesthetic reasons but normally for vision correction or eye protection. ... A soft contact lens A contact lens (also known as contact, for short) is a corrective or cosmetic lens placed on the cornea of the eye atop the iris. ...

Technological development

The LASIK technique was made possible by the Colombian-based Spanish ophthalmologist Jose Barraquer, who, around 1950 in his clinic in Bogotá, Colombia, developed the first microkeratome, used to cut thin flaps in the cornea and alter its shape, in a procedure called keratomileusis. He also provided the knowledge about how much of the cornea had to be left unaltered to provide a stable long-term result. José Ignacio Barraquer (January 24, 1916; Barcelona, Spain – February 13, 1998) was a Spanish ophthalmologist known to many as the father of modern refractive surgery. Barraquer invented the cryolathe and microkeratome and developed the surgical procedures of keratomileusis and keratophakia. ... For other uses, see Bogotá (disambiguation). ... A microkeratome is a precision surgical instrument with an oscillating blade designed for creating the corneal flap in LASIK or ALK surgery. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... Keratomileusis is the surgical improvement of the refractive state of the cornea performed by lifting up the front surface of the eye by forming a thin hinged flap under which the shape of the cornea is changed by using an excimer laser or other surgical device. ...

Later technical and procedural developments included the RK (Radial Keratectomy) started in the 70’s in Russia by Svyatoslav Fyodorov and the development of PRK (Photo Refractive Keratomileusis) in the 80’s in Germany by Theo Seiler.

In 1968, at the Northrup Corporation Research and Technology Center of the University of California, Mani Lal Bhaumik and a group of other scientists, while working on the development of a carbon-dioxide laser, would develop the Excimer laser, where molecules that do not normally exist come into being when xenon, argon or krypton gases are excited. This would form the cornerstone for LASIK eye surgery. Dr. Bhaumik announced his discovery in May of 1973 at a meeting of the Denver Optical Society of America in Denver, Colorado. He would later patent it. [1] Berkeley Davis Irvine Los Angeles Merced San Diego Santa Barbara Santa Cruz UC Office of the President in Oakland The University of California (UC) is a public university system in the state of California. ... Mani Bhaumik (Bengali: মণিলাল ভৌমিক) is a well-known physicist from India who helped develop the first excimer laser at the University of Californias famous Northrop Corporation Research and Technology Center. ... An excimer laser is a form of ultraviolet chemical laser which is commonly used in eye surgery and semiconductor manufacturing. ... Nickname: Location of Denver in Colorado Location of Colorado in the United States Coordinates: , Country State Founded [1] November 22, 1858 Incorporated November 7, 1861 Government  - Type Strong Mayor/Weak Council  - Mayor John Hickenlooper (D) Area [1]  - City & County  154. ...

The introduction of Laser in this refractive procedure started with the developments in Laser technology by Rangaswamy Srinivasan. In 1980, Srinivasan, working at IBM Research Lab, discovered that an ultraviolet excimer laser could etch living tissue in a precise manner with no thermal damage to the surrounding area. He named the phenomenon Ablative Photodecomposition (APD).[2]. Dr. Stephen Trokel published a paper in the American Journal of Ophthalmology in 1983, outlining the potential of using the excimer laser in refractive surgeries. Rangaswamy Srinivasan (Born February 28, 1929) is inventor at IBM Research. ... IBM Research, a subsidiary of IBM, has existed since 1945 and currently consists of eight locations throughout the world and hundreds of projects. ... An excimer laser is a form of ultraviolet chemical laser which is commonly used in eye surgery and semiconductor manufacturing. ...

Using these advances in laser technology and the technical and theoretical developments in refractive surgery made since the 50's, LASIK surgery was developed in 1990 by Lucio Buratto (Italy) and 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 in comparison with these former two techniques. Today, faster lasers, larger spot areas, bladeless flap incision, and wavefront-optimized and -guided techniques have significantly improved the reliability of the procedure as compared to that of 1991. Nonetheless, the fundamental limitations of excimer lasers and undesirable destruction of the eye's nerves have spawned research into many alternatives to "plain" LASIK, including all-femtosecond correction (Femtosecond Lenticule EXtraction, FLIVC), LASEK, Epi-LASIK, sub-Bowman’s Keratomileusis aka thin-flap LASIK, wavefront-guided PRK, and modern intraocular lenses. Keratomileusis is the surgical improvement of the refractive state of the cornea performed by lifting up the front surface of the eye by forming a thin hinged flap under which the shape of the cornea is changed by using an excimer laser or other surgical device. ... Photorefractive keratectomy (PRK) and Laser-Assisted Sub-Epithelial Keratectomy (LASEK) are laser eye surgery procedures intended to correct a persons vision and reduce their dependency on glasses or contact lenses. ... Femtosecond Lenticule EXtraction (FLEX) is a new form of refractive eye surgery similar to LASIK that creates a lenticule for removal and a corneal flap, all with a femtosecond laser. ... There are very few or no other articles that link to this one. ... This article or section should be merged with Photorefractive keratectomy LASEK, an acronym for Laser-Assisted Sub-Epithelial Keratectomy, is an eye surgery procedure intended to reduce a persons dependency on glasses or contact lenses. ... Epi-LASIK is a refractive surgery technique invented by Dr Ioannis Pallikaris (Crete, Greece). ... An intraocular lens (IOL) is an implanted lens in the eye, usually replacing the existing crystalline lens because it has been clouded over by a cataract, or as a form of refractive surgery to change the eyes optical power. ...

Procedure

There are several necessary preparations in the preoperative period. The operation itself is made by creating a thin flap on the eye, folding it to enable remodeling of the tissue underneath with laser. The flap is repositioned and the eye is left to heal in the postoperative period.

Preoperative

Patients wearing soft contact lenses typically are instructed to stop wearing them approximately 10 to 15 days before surgery. One industry body recommends that 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 patient's corneas are examined with a pachymeter to determine their thickness, and with a topographer to measure their surface contour. Using low-power lasers, a topographer 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. A soft contact lens A contact lens (also known as contact, for short) is a corrective or cosmetic lens placed on the cornea of the eye atop the iris. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... A pachymeter is a medical device used to measure the thickness of the eyes cornea. ... For other uses, see Laser (disambiguation). ... // Topographic maps are a variety of maps characterized by large-scale detail and quantitative representation of relief, usually using contour lines in modern mapping, but historically using a variety of methods. ... Astigmatism is an affliction of the eye, where vision is blurred by an irregularly shaped cornea. ...

Operation

The operation is performed with the patient awake and mobile; however, the patient typically is given a mild sedative (such as Valium) and anesthetic eye drops. A sedative is a substance that depresses the central nervous system (CNS), resulting in calmness, relaxation, reduction of anxiety, sleepiness, and slowed breathing, as well as slurred speech, staggering gait, poor judgment, and slow, uncertain reflexes. ... Diazepam, brand names: Valium, Seduxen, in Europe Apozepam, is a 1,4-benzodiazepine derivative, which possesses anxiolytic, anticonvulsant, sedative and skeletal muscle relaxant properties. ... Eye drops are saline-containing drops used as a vector to administer medication in the eye. ...

LASIK is performed in two steps. The first step is to create a flap of corneal tissue. The second step is remodeling of the cornea underneath the flap with laser. Finally, the flap is repositioned.

Flap creation

A corneal suction ring is applied to the eye, holding the eye in place. This step in the procedure can sometimes cause small blood vessels to burst, resulting in bleeding or subconjunctival hemorrhage into the white (sclera) of the eye, a harmless side effect that resolves within several weeks. Increased suction typically causes a transient dimming of vision in the treated eye. Once the eye is immobilized, the flap is created. This process is achieved with a mechanical microkeratome using a metal blade, or a femtosecond laser microkeratome (procedure known as IntraLASIK) that creates a series of tiny closely arranged bubbles within the cornea.[4] A hinge is left at one end of this flap. The flap is folded back, revealing the stroma, the middle section of the cornea. The process of lifting and folding back the flap can be uncomfortable. A subconjunctival hemorrhage is a common and relatively minor post-LASIK complication. ... Schematic diagram of the human eye. ... A microkeratome is a precision surgical instrument with an oscillating blade designed for creating the corneal flap in LASIK or ALK surgery. ... A femtosecond is the SI unit of time equal to 10-15 of a second. ... This article or section does not cite its references or sources. ... Stroma can refer to: The connective supportive framework of a biological cell, tissue, or organ. ...

Laser remodeling

The second step of the procedure is to use an excimer laser (193 nm) to remodel the corneal stroma. The laser vaporizes tissue in a finely controlled manner without damaging adjacent stroma. No burning with heat or actual cutting is required to ablate the tissue. The layers of tissue removed are tens of micrometers thick. Performing the laser ablation in the deeper corneal stroma typically provides for more rapid visual recovery and less pain, than the earlier technique photorefractive keratectomy (PRK). An excimer laser is a form of ultraviolet chemical laser which is commonly used in eye surgery and semiconductor manufacturing. ... Evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. ... A micrometre (American spelling: micrometer, symbol µm) is an SI unit of length equal to one millionth of a metre, or about a tenth of the diameter of a droplet of mist or fog. ... // Photorefractive keratectomy (PRK) and Laser-Assisted Sub-Epithelial Keratectomy (LASEK) are laser eye surgery procedures intended to correct a persons vision and reduce their dependency on glasses or contact lenses. ...

During the second step, the patient's vision will become very blurry once the flap is lifted. He/she will be able to see only white light surrounding the orange light of the laser. This can be disorienting.

Currently manufactured excimer lasers use an eye tracking system that follows the patient's eye position up to 4,000 times per second, redirecting laser pulses for precise placement within the treatment zone. The energy of each pulse is usually in the milliwatt range [5] Typically, each pulse is on the order of 10–20 nanoseconds.

Reposition of flap

After the laser has reshaped the stromal layer, the LASIK flap is carefully repositioned over the treatment area by the surgeon, and checked for the presence of air bubbles, debris, and proper fit on the eye. The flap remains in position by natural adhesion until healing is completed.

Postoperative

Patients are usually given a course of antibiotic and anti-inflammatory eye drops. These are discontinued in the weeks following surgery. Patients are also given a darkened pair of goggles to protect their eyes from bright lights and protective shields to prevent rubbing of the eyes when asleep.

Higher-order aberrations

Higher-order aberrations are visual problems not captured in a traditional eye exam which tests only for acuteness of vision. Severe aberrations can effectively cause significant vision impairment. These aberrations include starbursts, ghosting, halos, double vision, and a number of other post-operative complications listed below. Look up aberration in Wiktionary, the free dictionary. ...

Concern has long plagued the tendency of refractive surgeries to induce higher-order aberration not correctable by traditional contacts or glasses. The advancement of LASIK technique and technologies has helped reduce the risk of clinically significant visual impairment after the surgery. One of the major discoveries was the correlation between pupil size and aberrations:^[2] Effectively, the larger the pupil size, the greater the risk of aberrations. This correlation is the result of the irregularity between the untouched part of the cornea and the reshaped part. Daytime post-lasik vision is optimal, since the pupil is smaller than the LASIK flap. But at night, the pupil may expand such that light passes through the edge of the LASIK flap into the pupil which gives rise to many aberrations. There are other currently unknown factors in addition to pupil size that also affect higher order aberrations.

In extreme cases, where ideal technique was not followed and before key advances, some people could suffer rather debilitating symptoms including serious loss of contrast sensitivity in poor lighting situations.

Over time, most of the attention has been focused on spherical aberration. LASIK and PRK tend to induce spherical aberration, because of the tendency of the laser to undercorrect as it moves outward from the center of the treatment zone. This is really a significant issue for only large corrections. There is some thought if the lasers were simply programmed to adjust for this tendency, no significant spherical aberration would be induced. Hence, in eyes with little existing higher order aberrations, "wavefront optimized" lasik rather than wavefront guided LASIK may well be the future. Focal plane Longitudinal sections In optics, spherical aberration is an image imperfection that occurs due to the increased refraction of light rays that occurs when rays strike a lens or mirror near its edge, in comparison with those that strike nearer the center. ...

In any case, higher order aberrations are measured in µm (micrometers) on the wavescan taken during the pre-op examination, while the smallest beam size of FDA approved lasers is about 1000 times larger, at 0.65 mm. Thus imperfections are inherent in the procedure and a reason why patients experience halo, glare, and starburst even with a small naturally dilated pupils in dim lighting.

Wavefront-guided LASIK

Wavefront-guided LASIK^[3] 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, guiding the computer-controlled excimer laser with 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. In older patients though, scattering from microscopic particles plays a major role and may exceed any benefit from wavefront correction. Hence, patients expecting so-called "super vision" from such procedures may be disappointed. However, while unproven, 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. Ophthalmology is the branch of medicine which deals with the diseases of the eye and their treatment. ... Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ... Focal plane Longitudinal sections In optics, spherical aberration is an image imperfection that occurs due to the increased refraction of light rays that occurs when rays strike a lens or mirror near its edge, in comparison with those that strike nearer the center. ...

Complications

A subconjunctival hemorrhage is a common and minor post-LASIK complication.

The incidence of refractive surgery patients having unresolved complications six months after surgery has been estimated from 3%^[4] to 6%.^[5] The following are some of the more frequently reported complications of LASIK^[6][6]: Image File history File links Picture of a post-LASIK hemorrhage of the eye Taken by Raul654 on July 14, 2005. ... Image File history File links Picture of a post-LASIK hemorrhage of the eye Taken by Raul654 on July 14, 2005. ... A subconjunctival hemorrhage is a common and relatively minor post-LASIK complication. ...

• Surgery induced dry eyes
• Overcorrection^[7] or undercorrection
• Visual acuity fluctuation
• Halos^[8] or starbursts^[9] around light sources at night
• Light sensitivity
• Ghost images^[10] or double vision
• Wrinkles in flap (striae)^[11]
• Decentered ablation
• Debris or growth under flap
• Thin or buttonhole flap ^[12]
• Induced astigmatism
• Corneal Ectasia
• Epithelium erosion
• Posterior vitreous detachment^[13]
• Macular hole^[14]

Complications due to LASIK have been classified as those that occur due to preoperative, intraoperative, early postoperative, or late postoperative sources:^[15] Keratoconjunctivitis sicca or KCS is an eye disease caused by decreased tear production or increased tear film evaporation commonly found in people and small animals. ... Traditional Snellen chart used for visual acuity testing. ... Diplopia, commonly known as double vision, is the perception of two images from a single object. ... Astigmatism is an affliction of the eye, where vision is blurred by an irregularly shaped cornea. ... A posterior vitreous detachment (PVD) is an ocular condition in which there is a separation of the vitreous humor from the retina. ... Human eye cross-sectional view. ...

Intraoperative complications

• The incidence of flap complications has been estimated to be 0.244%.^[16] 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^[17] but rarely lead to permanent visual acuity loss; the incidence of these microkeratome-related complications decreases with increased physician experience.^[18][19] This risk is further reduced by the use of IntraLasik and other non-microkeratome related approaches.
• 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. A faster operation may decrease the chance of this complication, as there is less time for the flap to dry.
• Flap interface particles are another finding whose clinical significance is undetermined.^[20] 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.^[20]

This article or section does not cite its references or sources. ... The slit-lamp examination looks at structures that are at the front of the eye (the anterior segment): The eyelid, the sclera (white outer structure of the eye), conjunctiva (membranes lining the eyelid and sclera surface), iris (colored part of the eye), natural crystalline lens, and the cornea (thin transparent... Confocal microscopy is an imaging technique used to increase micrograph contrast and/or to reconstruct three-dimensional images by using a spatial pinhole to eliminate out-of-focus light or flare in specimens that are thicker than the focal plane. ...

Early postoperative complications

• The incidence of diffuse lamellar keratitis (DLK)[7], also known as the Sands of Sahara syndrome, has been estimated at 2.3%.^[21] When diagnosed and appropriately treated, DLK resolves with no lasting vision limitation.
• The incidence of infection responsive to treatment has been estimated at 0.4%.^[21] Infection under the corneal flap is possible. It is also possible that a patient has the genetic condition keratoconus that causes the cornea to thin after surgery. Although this condition is screened 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 may need rigid gas permeable contact lenses, Intrastromal Corneal Ring Segments (Intacs),^[22] Corneal Collagen Crosslinking with Riboflavin^[23] or 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.^[5] 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.^[24] Some patients experience reactive tearing, in part to compensate for chronic decreased basal wetting tear production.
• The incidence of subconjunctival hemorrhage has been estimated at 10.5% ^[21](according to a study undertaken in China; thus results may not be generally applicable due to racial and geographic factors).

An infection is the detrimental colonization of a host organism by a foreign species. ... Keratoconus (from Greek: kerato- horn, cornea; and konos cone), is a degenerative non-inflammatory disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve. ...

Late postoperative complications

• The incidence of epithelial ingrowth has been estimated at 0.1%.^[21]
• Glare is another commonly reported complication of those who have had LASIK.^[25]
• 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.^[26] In daytime, the pupil is smaller than the edge. Modern equipment is better suited to treat those with large pupils, and responsible physicians will check for them during examination.
• Late traumatic flap dislocations have been reported 1–7 years post-LASIK.^[27]

This time exposure photo of New York City shows sky glow, one form of light pollution. ...

Other

Lasik and other forms of laser refractive surgery (i.e. PRK,LASEK and Epi-LASEK) change the dynamics of the cornea. These changes make it difficult for your optometrist and ophthalmologist to accurately measure your intraocular pressure, essential in glaucoma screening and treatment. The changes also affect the calculations used to select the correct intraocular lens implant when you have cataract surgery. This is known to ophthalmologists as a "refractive surprise". The correct intraocular pressure and intraocular lens power can be calculated if you can provide your eye care professional with your preoperative, operative and postoperative eye measurements. Many refractive surgeons don't disclose this information to their patients and certainly don't provide the medical record. Years after your refractive surgery (unless you obtained and stored your medical record) this information will not be available when you need it.

Although there have been improvements in LASIK technology^[28][29][30] , a large body of conclusive evidence on the chances of long-term complications is not yet established. Also, there is a small chance of complications, such as slipped flap, corneal infection, haziness, halo, or glare some of which are irreversible because the LASIK eye surgery procedure is irreversible.

The incidence of macular hole has been estimated at 0.2 per cent^[14] to 0.3 per cent.^[31] The incidence of retinal detachment has been estimated at 0.36 per cent.^[31] The incidence of choroidal neovascularization has been estimated at 0.33 per cent.^[31] The incidence of uveitis has been estimated at 0.18 per cent^[32] Vitrectomy. ... Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. ... Uveitis specifically refers to inflammation of the middle layer of the eye, termed the uvea but in common usage may refer to any inflammatory process involving the interior of the eye. ...

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 to avoid structurally weakening the cornea. Decreased atmospheric pressure at higher altitudes has not been demonstrated as extremely dangerous to the eyes of LASIK patients, however, some mountain climbers have experienced a myopic shift at extreme altitudes.^[33][34] There are no published reports documenting scuba diving-related complications after LASIK.^[35] Mountaineering is an umbrella term that can variously be used to describe the actions of climbing, hillwalking and scrambling. ...

In situ keratomileusis effected at a later age increases the incidence of corneal higher-order wavefront aberrations.^[36][37] Conventional eyeglasses do not correct higher order aberrations.

Microfolding has been reported as "an almost unavoidable complication of LASIK" whose "clinical significance appears negligible".^[20]

Myopic (nearsighted) people who are close to the age (mid- to late-forties) when they will require either reading glasses or bifocal eyeglasses, may find that they still require reading glasses despite having undergone refractive LASIK surgery. Myopic people generally require reading glasses or bifocal eyeglasses at a later age than people who are emmetropic (those who see without eyeglasses), but this benefit is lost if they undergo LASIK. This is not a complication, but an expected result of the physical laws of optics.

Factors affecting surgery

Typically, the cornea is avascular, because it must be transparent to function normally, its cells absorbing oxygen from the tear film. Thus, low oxygen-permeable contact lenses reduce the cornea's oxygen absorption, sometimes resulting in corneal neovascularization—the growth of blood vessels into the cornea. This causes a slight lengthening of inflammation duration and healing time and some pain during surgery, because of greater bleeding. General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... The tear system. ...

Although some contact lenses (notably modern RGP and soft silicone hydrogel lenses), are made of materials with greater oxygen permeability that help reduce the risk of corneal neovascularization, patients considering [LASIK] are warned to avoid over-wearing their contact lenses. Usually, it is recommended that they discontinue wearing contact lenses days or weeks before the LASIK eye surgery.

A 2004 Wake Forest University study established that heat and humidity affect LASIK surgery results, both during the procedure and in the two weeks before the surgery.^[38] Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... Wake Forest University is a private, coeducational university located in Winston-Salem, North Carolina. ...

Patient satisfaction

The surveys determining patient satisfaction with LASIK, have found most patients satisfied, with satisfaction range being 92–98 percent.^{[25][39][40][41]}

Some patients with poor outcomes from LASIK surgical procedures report a significantly reduced quality of life because of vision problems. Patients who have suffered LASIK complications have published websites^[42] to educate the public about the risks, and discussion forums,^{[43][44][45][46]} where prospective and past patients can discuss the surgery.

Safety and efficacy

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 percent 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.^[47] A 2003 study, reported in the medical journal Ophthalmology, found that nearly 18 percent of treated patients and 12 percent of treated eyes needed retreatment.^[48] 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^[49][50] before issuing guidance for the use of LASIK within the NHS.^[51] 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." “NHS” redirects here. ... The National Institute for Health and Clinical Excellence or NICE is an agency of the National Health Service in the United Kingdom. ... Systematic reviews are named as the highest level of medical evidence, by evidence based medicine professionals. ...

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.^[52][53]

On October 10, 2006, WebMD reported that statistical analysis revealed that contact lens wear infection risk is greater than the infection risk from LASIK.^[54] Daily contact lens wearers have a 1-in-100 chance of developing a serious, contact lens-related eye infection in 30 years of use, and a 1-in-2,000 chance of suffering significant vision loss as a result of infection. The researchers calculated the risk of significant vision loss consequence of LASIK surgery to be closer to 1-in-10,000 cases. is the 283rd day of the year (284th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ...

On February 21, 2007, the Food and Drug Administration (FDA) issued a Class I recall of the LADAR-6000 surgical laser, manufactured by Alcon.^{[55] [56]} The recall was because the algorithm used to calculate the laser treatment left some patients with inaccurate surgical outcomes that could not be re-treated with additional surgery. is the 52nd day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... “FDA” redirects here. ... Alcon, (NYSE: ACL) headquartered in Hünenberg, Switzerland, is a global medical company specializing in eye care products. ... In mathematics, computing, linguistics, and related disciplines, an algorithm is a finite list of well-defined instructions for accomplishing some task that, given an initial state, will terminate in a defined end-state. ...

References

See also

• Council for Refractive Surgery Quality Assurance
• LASEK (Laser-Assisted Sub-Epithelial Keratectomy) or PRK (Photorefractive keratectomy)
• Radial keratotomy
• Refractive error
• Refractive surgery
• Wavefront

The Council for Refractive Surgery Quality Assurance (CRSQA) is an independent, nonprofit, patient/consumer health organization that provides detailed information about LASIK and certifies refractive surgery doctors based upon patient outcomes. ... This article or section should be merged with Photorefractive keratectomy LASEK, an acronym for Laser-Assisted Sub-Epithelial Keratectomy, is an eye surgery procedure intended to reduce a persons dependency on glasses or contact lenses. ... // Photorefractive keratectomy (PRK) and Laser-Assisted Sub-Epithelial Keratectomy (LASEK) are laser eye surgery procedures intended to correct a persons vision and reduce their dependency on glasses or contact lenses. ... Radial keratotomy (RK) is a refractive surgical procedure to correct myopia. ... Refraction error, also known as refractive error, is an error in the focusing of light by the eye and a frequent reason for reduced visual acuity. ... Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease dependency on glasses or contact lenses. ... In optics, a wavefront is the locus (a line or surface in an electromagnetic wave) of points having the same phase. ...

External links

• FDA information page on LASIK
• Free LASIK Consumer Report Free Educational Guide about LASIK
• University of Illinois page on LASIK Educational videos and full-text peer-reviewed journal articles on LASIK
• Vision Surgery Rehab Network Support site for people with complications from LASIK and other eye surgeries.
• ComplicatedEyes.org Resources for patients with Lasik and other eye surgery complications.
• Ectasia complications management with Intacs, C3-R, and CK
• U.S. National library of medicine
• Eye surgery education council LASIK faqs
• Study confirms safety of Lasik surgery10 year study confirms safety of lasik surgery