Photorefractive keratectomy (PRK) and laser-assisted in-situ keratomileusis (LASIK) are two similar surgical techniques that use an excimer laser to correct nearsightedness (myopia) by reshaping the cornea. The cornea is the clear outer structure of the eye that lies in front of the colored part of the eye (iris). PRK and LASIK are two forms of vision-correcting (refractive) surgery. The two techniques differ in how the surface layer of the cornea is treated. As of mid 1998, two eximer lasers (Summit and Visx) had been approved for laser vision correction (refractive surgery using a laser) in the PRK procedure. Since then, Visx, Summit, and other lasers have received approval by the Food and Drug Administration (FDA) for use in LASIK procedures.
Description
PRK and LASIK are both performed with an excimer laser, which uses a cold beam of ultraviolet light to sculpt or reshape the cornea so that light will focus properly on the retina. The cornea is the major focusing structure of the eye. The retina sends the image focused on it to the brain. In myopia, the cornea is either too steep or the eye is too long for a clear image to be focused on the retina. PRK and LASIK flatten out the cornea so that the image will focus more precisely on the retina.
In PRK, the surface of the cornea is removed by the laser. In LASIK, the outer layer of the cornea is sliced, lifted, moved aside while the cornea is reshaped with the laser, then replaced to speed healing. Both procedures cause the cornea to become flatter, which corrects the nearsighted vision.
At least one laser has been approved to treat mild astigmatism as of 2000. Correcting farsightedness (hyperopia) may be possible in the future.
These laser vision-correcting procedures are rapidly replacing radial keratotomy (RK), an earlier form of refractive surgery that involved cutting the cornea with a scalpel in a pattern of radiating spokes. RK has declined in popularity since the approval of the excimer laser in 1995, falling from a high of 250,000 procedures performed per year in 1994 to 50,000 in 1997.
For both LASIK and PRK, the patient's eye is numbed with anesthetic drops. No injections are necessary. The patient is awake and relaxed during the procedure.
LASIK is sometimes referred to as a "flap and zap" procedure because a thin flap of tissue is temporarily removed from the surface of the cornea and the underlying cornea is then "zapped" with a laser. Prior to the surgery, the surface of the cornea is marked with a dye marker so that the flap of cornea can be precisely aligned when it is replaced. The doctor places a suction ring on the eye to hold it steady. During this part of the operation, which lasts only a few seconds, the patient is not able to see. A surgical instrument called a microkeratome is passed over the cornea to create a very thin flap of tissue. The IOP is increased at this time which is why it is contraindicated in patients with glaucoma. This thin tissue layer is folded back. The cornea is reshaped with the laser beam and the cell layer is replaced. Because the cell layer is not permanently removed, patients have a faster recovery time and experience far less discomfort than with PRK. An antibiotic drop is put in and the eye is patched until the following day's checkup.
In PRK, a small area of the surface layer of the cornea is vaporized. It takes about three days for the surface cells to grow back and vision will be blurred. Some patients describe it as "looking through Vaseline." PRK is generally recommended for patient's with mild to moderate myopia (usually under-5.00 diopters).
With both PRK and LASIK, there is a loud tapping sound from the laser and a burning smell as the cornea is reshaped. The surgery itself is painless and takes only a minute or two. Patients are usually able to return home immediately after surgery. Most patients wait (up to six months) before they have the second one done. This allows the first eye to heal and to see if there were complications from the surgery.
The cost of these procedures can vary with geographic area and the doctor. In general, the procedure costs $1,350–$2,500 per eye for PRK and about $500 more per eye for LASIK. PRK and LASIK are generally not covered by insurance. However, insurance may cover these procedures for people in certain occupations, such as police officers and firefighters.
Who Performs the Procedure and Where Is It Performed?
An ophthalmologist performs LASIK, but because it is a relatively new technology, the surgeon may not have received training as part of his residency. It is more likely the surgeon has completed continuing medical education courses or may have had training provided by the laser companies. He may also have received training as part of membership in an organization such as the American Society of Refractive Surgeons.
Before and aftercare probably will be provided by a co-managing optometrist. The optometrist usually performs the pre- and post-operative exams, and also discusses the patient's suitability for LASIK and any potential problems.
Ophthalmic technicians may perform preliminary testing, including corneal topography and corneal measuring. Laser technicians are required to have special training provided by the laser manufacturer.
Surgeons may perform LASIK in a hospital where they rely on the hospital staff for support. Because lasers are expensive, some surgeons pool their resources and purchase a laser that they share at a freestanding surgery center. LASIK is also provided by surgeons at surgery centers owned by refractive surgery companies. These businesses hire support staff, optometrists and surgeons to perform LASIK.
Questions to Ask the Doctor
How many LASIK procedures have you performed and how long have you been performing them?
Who will handle the aftercare, the ophthalmologist or co-managing optometrist?
What is the experience of the laser support team?
How many of your patients achieve 20/20 or better?
What percentage of your patients have serious complications? Minor complications?
Who will treat complications, if any, after the procedure?
If the patient needs an enhancement, is that an extra expense, or is it covered in the original fee?
LASIK is an elective surgery for patients who want to permanently correct myopia (nearsightedness), hyperopia (farsightedness), or astigmatism without eyeglasses, contact lenses, or refractive surgical procedures. The goal for most patients is to be free of any type of corrective lenses. Some patients may find wearing eyeglasses or contact lenses interferes with their careers or hobbies. Many professional athletes have chosen LASIK to improve their performance. However, patients with higher degrees of refractive error will still need some type of corrective lens.
LASIK is most commonly performed on myopes. For myopia, the surgeon flattens the cornea; for hyperopia, the surgeon steepens the cornea. Surgeons correct astigmatism by creating a normally shaped cornea with the excimer laser.
A new type of LASIK also can treat contrast sensitivity as well as refractive error. Custom LASIK incorporates new eye mapping technology into standard LASIK. The surgeon measures the eye from front to back creating a three dimensional corneal map. This much-more detailed map gives surgeons more specific information for the excimer laser and enables them to correct other abnormalities besides refractive error.
Demographics
LASIK candidates have myopia, hyperopia, or astigmatism; are 18 or older; and have had stable vision for at least two years. The American Academy of Ophthalmology (AAO) estimated that 1.8 million refractive surgery procedures were performed in 2002. LASIK was estimated to account for 95% of those procedures.
The first LASIK patients in the late 1990s were in the upper class, or upper middle class, and in their early 30s to mid-40s. The market was limited for the elective procedure that at first could range as expensive as $5,000 per eye. The number of younger patients receiving LASIK (in their early to mid-20s) was expected to rise in 2003 and beyond. The number of procedures also was expected to increase as prices continued to stabilize, and surgery centers and physicians offered payment plans.
Description
LASIK is a relatively new procedure. In April 1985, German physician Theo Seiler was the first to use an excimer laser to attempt to correct astigmatism in blind eyes. Experiments with excimer lasers on blind eyes were also completed in the United States in the mid-1980s. The term LASIK was invented by Greek ophthalmologist Ioannis Pallikari, the first surgeon to use the hinged flap technique. Dr. Stephen Brint, as part of a clinical trial in 1991, performed the first LASIK procedure in the United States.
As of 2003, there are two types of LASIK. The standard LASIK procedure and custom LASIK, which relatively few surgeons have the technology to perform.
Standard Lasik
Standard LASIK takes from 10 to 20 minutes to perform and the results are immediate. It's standard practice in LASIK operating rooms to have a clock on the wall so patients immediately can note they are able to read a clock face or other items that previously were blurry.
Immediately before the procedure, the ophthalmologist may request corneal topography (a corneal map) to compare with previous maps to ensure the treatment plan is still correct. The surgeon may also measure the cornea's thickness if he didn't previously. After these tests, a technician or co-managing optometrist will perform a refraction to make sure the refractive correction the surgeon will program into the laser is correct.
Three sets of eye drops will be administered twice before surgery. The first drop anesthetizes the cornea, the second drop prevents infection and the third drop controls inflammation after LASIK. Patients may be given a sedative, such as Valium. This is administered to calm nervous patients or to help patients sleep after the procedure.
After the prep work is completed, the patient reclines on a laser bed and the surgeon is seated directly behind the patient. If the procedure is being done on both eyes on the same day, the surgeon will patch the second eye. An eyelid speculum is inserted in the eye to be treated first to hold the eyelids apart. The patient stares at the
In LASIK surgery, the eye is held open with a speculum, and a suction ring is attached to the eyeball (A). A microkeratome is used to shave the protective flap off the top of the eye (B), which is then pulled back (C). A computer-controlled laser is used to reshape the cornea (D), and the protective flap is replaced (E). (Illustration by GGS Inc.)
blinking light of a laser microscope and must fixate his or her gaze on that light. The patient must remain still throughout the procedure.
The surgeon checks the refractive numbers on the laser. Because each patient's cornea is shaped differently, the surgeon may have to adjust the level of correction. Laser companies provide an algorithm to determine the correction level, and the surgeon may alter the level because of a patient's special needs. The adjustments are called nomograms. After the adjustments, the surgeon checks the microkeratome blade for defects.
The surgeon then indents the cornea to mark the flap location. The surgeon places a suction ring in the center of the sclera. A technician will activate the microkeratome's suction. The patient's vision dims at this point. The surgeon tests pressure by touching the cornea with a tonometer. Before using the microkeratome, sterile saline solution is squirted into the suction ring to lubricate the cornea. The microkeratome head is placed in the gear tracks of the suction ring, and the surgeon guides the microkeratome across the suction ring to create a flap. The microkeratome stops just short of traveling completely across the cornea. It leaves a hinge of tissue, commonly called a flap. After the flap is created, the surgeon removes the suction ring and slips a spatula under it and moves it to the side, exposing the stroma (inner cornea).
Once the stroma is exposed, the laser ablation begins, ranging from 30 to 60 seconds. The ablation flattens the cornea of myopic patients; steepens the cornea of hyperopic patients; and reshapes the cornea of astigmatic patients. After the ablation, the surgeon replaces the flap. More saline solution is squirted to remove any debris and enable the flap to move back into place without interruption. The surgeon ensures the flap is in place and removes any wrinkles. The surgeon places a shield over the eye to keep the flap in place. No stitches are used.
If bilateral LASIK is being performed, the patient must remain still while he is prepared for treatment on the remaining eye.
Custom Lasik
As of early 2003, a handful of ophthalmologists in the United States had the technology to perform custom LASIK. The difference between standard LASIK and custom LASIK lies in the diagnosis and who can be treated. With custom LASIK, surgeons use a wavefront analyzer (aberrometer) that beams light through the eye and finds irregularities based on how the light travels through the eye. It creates a three-dimensional corneal map to create a customized pattern for each patient. For standard LASIK, each patient with the same refractive error is treated with the same setting on the excimer laser, barring a few adjustments. The new technology individualizes treatment not only for refractive errors, but also for visual disorders that previous corneal mapping technology could not detect. As of early 2003, there was only one FDA-approved laser capable of the customized ablations, but others were awaiting approval.
Besides the customized excimer laser, the surgical procedure is the same. Surgeons now can treat patients who have higher-order aberrations, such as contrast sensitivity. Therefore, custom LASIK can successfully treat glare, night vision and other contrast problems.
Diagnosis/Preparation
Before LASIK, patients need to have a complete eye evaluation and comprehensive medical history taken. Soft contact lens wearers should stop wearing their lenses at least one week before the initial exam. Gas permeable lens wearers should not wear their lenses from three weeks to a month before the exam. Contact lens wear can alter the cornea's shape, which should be allowed to return to its natural shape before the initial exam.
The Initial Exam
During the first exam, the surgeon's staff will take a comprehensive medical history to determine if there are underlying medical problems that will prevent a successful surgery. This screening process will determine patients who should not have the procedure including:
pregnant women or women who are breastfeeding
patients with very small or very large refractive errors
The physician will also ask about medication. Some prescription medicines have been known to cause post-surgical scarring or cause flecks under the corneal flap. It's important for the patient to disclose any prescriptions or over-the-counter medicines taken regularly. Allergies to prescription medicine must also be discussed.
A complete eye exam will be performed to determine refractive error, uncorrected visual acuity and best corrected visual acuity. A cycloplegic refraction using eye drops to dilate the pupils also will be performed. Other examination procedures include corneal mapping, a keratometer reading to determine the curvature of the central part of the cornea, a slit lamp exam to determine any damage to the cornea and evidence of glaucoma and cataracts. A fundus exam also will be performed to check for retinal holes and macular degeneration and macular disease. Other tests are done to rule out glaucoma.
While those tests check general eye health, others more closely relate to the outcome of LASIK surgery. A corneal pachymeter measures the cornea's thickness. This is important because surgeons remove tissue during surgery. A pupilometer measures the pupil when it is naturally dilated in a dark room without drops. Patients with large pupils have been known to have complications after LASIK, such as glare and halos.
Treatment Options/Informed Consent
After the exam, the patient and physician discuss treatment options and expectations. Patients who expect to see perfectly after LASIK are usually not considered good candidates because they usually are dissatisfied with the results. Surgeons also discuss how patients will handle presbyopia, which occurs during the patient's 40s. LASIK does not correct for presbyopia, and patients will need reading glasses to accommodate for reading when presbyopia occurs. Sometimes patients 40 and older opt for monovision to treat presbyopia, where one eye is left untreated or one eye is only partially corrected. Monovision means one eye is for short-term vision and the other is for distance vision.
The doctor will advise the patient of any possible LASIK complications, explain the procedure and answer questions. After deciding on a treatment option, the patient is required to sign an informed consent form.
At this time, payment will also be discussed. Insurance usually does not cover LASIK, although some offer a limited benefit for the procedure. Some laser centers offer payment plans and some physicians have begun using credit companies to handle payments. LASIK can cost anywhere from $999 to $3,000 per eye. The cost varies greatly from surgeon to surgeon. Most of the fees are global, and cover all the pre-operative and post-operative exams as well as the procedure. Patients should be advised of what the fee covers, and if retreatments to the original surgery are included in that price.
Pre-Surgery Preparations
The patient is advised to discontinue contact lens wear immediately and refrain from using creams, lotions, make-up or perfume for at least two days before surgery. Patients may also be asked to scrub their eyelashes for a period of time to remove any debris. Patients also must find transportation to and from the surgery, and also to and from the first post-operative visit. Medication and distorted vision make it unsafe for the patients to drive after LASIK.
Aftercare
After LASIK, patients may experience burning, itching or a foreign body sensation. They should be advised not to touch the eye as that could damage the flap. Many physicians recommend sleeping after the surgery. Patients may also experience glare, starbursts, or halos that should improve after the first few days. Patients are advised to seek help immediately if they feel severe eye pain, or if symptoms worsen.
The first follow-up visit is from 24 to 48 hours after surgery. The physician will remove the eye shield, check the patient's vision, and may prescribe more antibiotic drops or artificial tears. Patients must refrain from strenuous activity, such as contact sports, for at least a month. The use of creams, lotions, and make-up must also be avoided for at least two weeks. Hot tubs and swimming pools should be avoided for at least two months. Patients are advised that refraining from these activities and products will help stem infection and aid healing of the cornea.
Patients will have regularly scheduled visits post-LASIK for at least six months. Vision gradually improves the first few months after surgery. In some cases, if the vision does not meet expectations and the surgeon believes it can be further corrected, he will perform an enhancement. Enhancements are usually done for under-correction. Overcorrected patients usually need eyeglasses or contact lenses.
Risks
Surgeons separate LASIK complications into two categories.
Intraoperative Risks
Cornea perforation. This complication has almost disappeared because of advances in microkeratome design.
Flap complications. Newer microkeratomes also have reduced the likelihood of "free caps," where the cap becomes unhinged. An experienced surgeon replaces the cap after ablation. In some cases, the procedure must be aborted while the eye heals.
Laser hot spots. Higher energy surrounding the laser beam can cause irregular astigmatism. Proper laser testing before the procedure eliminates this risk.
Central islands. This refers to a raised area in the central part of the treated zone that receives insufficient laser treatment. Any raised area can decrease the laser's effectiveness. The island either shrinks by itself or can be remedied with retreatment.
Decentered ablation. This occurs when the laser beam is aimed incorrectly. This can result in permanent halos and ghost images.
Post-Operative Complications
Undercorrection or overcorrection. Undercorrection can usually be treated with an enhancement, but over-correction will require the use of eyeglasses or contact lenses.
Debilitating symptoms. These can be permanent or transient, and include glare, halos, double vision and poor nighttime vision. Some patients may also lose contrast sensitivity.
Dry eye. This also can be permanent or transient. Most patients experience some dry eye immediately after surgery. Some patients continue to experience dry eye and are treated with artificial tears or punctal plugs.
Displaced flap. Occurs after the eye is hit or rubbed. If immediate attention is given by the surgeon, who must lift the flap and clean under it, no long-term effects occur.
Nonspecific diffuse intralamellar keratitis. Commonly known as Sands of the Sahara, this complication can range from corneal haze to eye clouding that resembles swirling sand. It is treated with topical steroids, although severe cases may require eye irrigation.
Epithelial ingrowth. The cells of the lower cornea migrate under the corneal cap. The surgeon must lift the cap and remove the cells. If untreated, vision is impaired.
Striae. These are wrinkles in the flap that can reduce visual acuity. The surgeon must lift the corneal flap and smooth the wrinkles.
Photophobia. Extreme sensitivity to light can last a few days or a week after surgery.
Infection. This rarely occurs after LASIK. It is treated with antibiotics.
Normal Results
After LASIK, most patients are able to see well enough to pass a driver's license exam without glasses or contact lenses. Some patients will still need corrective lenses, but the lenses won't need to be as powerful.
Because LASIK is a relatively new procedure, there is limited information on long-term regression. If patients are being treated for myopia, they should be aware they will have to rely on spectacles with the onset of presbyopia.
Morbidity and Mortality Rates
Information about mortality rates following LASIK is limited because the procedure is elective. Complications that can lead to more serious conditions, such as infection, are treated with topical antibiotics after LASIK. The most serious possible complication from LASIK is blindness from an untreated complication. As of 2000, there had been no reports of blindness-induced LASIK. One incidence of legal blindness was reported after a severely myopic patient had retinal hemorrhages. However, it was inconclusive whether or not LASIK was the causative agent.
Alternatives
Nonsurgical Alternatives
Nonsurgical alternatives to LASIK are contact lenses and eyeglasses, which can also correct refractive errors. Continuous-wear contact lenses, which a patient can sleep in for as long as 30 days, can provide the same effect as LASIK if the patient wants good vision upon waking. Orthokeratology involves a rigid gas permeable contact lens the patient wears for a predetermined amount of time to reshape the cornea. After removing the lens, it takes weeks for the cornea to return to its normal shape. At that time, the patient repeats the process.
Corneal rings and implants are another alternative for myopes. These require surgery without lasers and involve a corrective lens surgically implanted in the eye. One of the biggest benefits to these procedures is that they are reversible. However, they may not provide the crisp vision of a successful LASIK. There also are several different types of intraocular lenses being tested to treat myopia and hyperopia.
Surgical Alternatives
There also are surgical alternatives to LASIK. They include:
Conductive keratoplasty. This uses radio frequency waves to shrink corneal collagen. It is used to treat mild to moderate hyperopia.
Photorefractive keratectomy (
Prk
). PRK also uses an excimer laser and is similar to LASIK. However, in PRK, the surface of the cornea is removed by the laser. PRK patients have a longer recovery time and may need steroidal eye drops for months after surgery. Its success rate is similar to that of LASIK.
Radial keratotomy (RK). RK was the first widely used surgical correction for mild to moderate myopia. The surgeon alters the shape of the cornea without a laser. This is one of the oldest refractive procedures, and has proved successful on lower and moderate corrections.
Astigmatic keratotomy (AK). AK is a variation of RK used to treat mild to moderate astigmatism. AK has proved successful if the errors are mild to moderate.
Laser thermal keratoplasty (LTK). LTK was approved as to treat hyperopia in 2000. An LTK patient's vision is overcorrected for one to three months, and the effect of improved near vision may diminish over time as distance vision improves. Some regression has been noted.
Resources
Books
Brint, Stephen F., M.D., Dennis Kennedy, O.D., and Corinne Kuypers-Denlinger. The Laser Vision Breakthrough Roseville, CA: Prima Health, 2000.
Caster, Andrew I., M.D., F.A.C.S. The Eye Laser Miracle: The Complete Guide to Better Vision New York, NY: Ballantine Books, 1997.
Slade, Stephen G., M.D., Richard Baker, O.D., and Dorothy Kay Brockman. The Complete Book of Laser Eye SurgeryNaperville, ILL: Sourcebooks, Inc., 2000.
Organizations
American Academy of Ophthalmology. PO Box 7424, San Francisco, CA 94120-7424 (415) 561-8500. http://www.aao.org
American Society of Cataract and Refractive Surgery. 4000 Legato Road, Suite 850, Fairfax, VA 22033-4055. (703) 591-2220. ascrs@ascrs.org. http://www.ascrs.org.
"LASIK Eye Surgery." U.S. Food and Drug Administration Center for Devices and Radiological Health. October 1, 2002 [cited February 20, 2003]. http://www.fda.gov/cdrh/lasik.
Acronym for laser in situ keratotomy, a procedure for eye surgery that corrects near-sightedness by using a laser to cut a flap in the cornea so that it flattens out. The end result is a better focusing of incoming light on the back of the retina.
LASIK or Lasik (laser-assisted in situkeratomileusis) is a type of refractive surgery for correcting myopia, hyperopia, and astigmatism. LASIK is performed by ophthalmologists using a laser.[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 a PRK/ASA procedure is medically justified as being a better alternative to LASIK.[citation needed]
Many patients choose LASIK as an alternative to wearing corrective eyeglasses or contact lenses.
The LASIK technique was made possible by the Colombia-based Spanish ophthalmologist Jose Barraquer, who, around 1950 in his clinic in Bogotá, Colombia, developed the first microkeratome, and developed the technique used to cut thin flaps in the cornea and alter its shape, in a procedure he called keratomileusis. Barraquer also researched the question of how much of the cornea had to be left unaltered to provide stable long-term results.
Later technical and procedural developments included RK (radial keratotomy), developed in Russia in the 1970s by Svyatoslav Fyodorov, and PRK (photorefractive keratectomy), developed in 1983 at Columbia University by Dr. Steven Trokel, who in addition published an article in the American Journal of Ophthalmology in 1983 outlining the potential benefits of using the Excimer laser in refractive surgeries. (RK is a procedure in which radial corneal cuts are made, typically using a micrometer diamond knife, and is completely different from LASIK).
In 1968 at the Northrop Corporation Research and Technology Center of the University of California, Mani Lal Bhaumik and a group of scientists were working on the development of a carbon-dioxide laser. Their work evolved into what would become the Excimer laser. This type of laser would become the cornerstone for refractive eye surgery. Dr. Bhaumik announced his team's breakthrough in May 1973 at a meeting of the Denver Optical Society of America in Denver, Colorado. He would later patent his discovery.[2]
The general term for changing a patient's optical measurements by means of an operation is Refractive Surgery. The introduction of lasers in refractive surgeries stemmed from Rangaswamy Srinivasan's work. 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).[3]
The first patent for LASIK was granted by the U.S. Patent Office to Dr. Gholam A. Peyman on June 20, 1989, U.S. Patent #4,840,175, "Method for modifying corneal curvature," encompassing the surgical procedure in which a flap is cut in the cornea and pulled back to expose the corneal bed. The exposed surface is then ablated to the desired shape with an Excimer laser, after which the flap is replaced.[citation needed]
The LASIK technique was successfully applied in other countries before it arrived to the United States. The first U.S. Food and Drug Administration (FDA) trial of the Excimer laser was started in 1989. The first use of the laser was to change the surface shape of the cornea, known as PRK. Dr. Joseph Dello Russo was one of the ten original FDA researchers who tested and got approval for the Visx laser. The LASIK concept was first introduced by Dr. Palliakaris in 1992 to the group of ten surgeons who were selected by the FDA to test the Visx laser at 10 centers in the U.S.
Dr. Palliakaris theorized the benefits of performing PRK after the surface was raised in a layer to be known as a flap performed by the Mikrokeratome developed by Barraquer in 1950. The blending of a flap and PRK became known as LASIK, which is an acronym. It quickly became very popular, since it provided immediate improvements in vision and involved much less pain and discomfort than PRK.
Today, faster lasers, larger spot areas, bladeless flap incisions, intraoperative pachymetry, and wavefront-optimized and -guided techniques have significantly improved the reliability of the procedure 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 LASEK, Epi-LASIK, sub-Bowman’s Keratomileusis aka thin-flap LASIK, wavefront-guided PRK and modern intraocular lenses.
LASIK may one day be replaced by intrastromal ablation[4] via all-femtosecond correction (like Femtosecond Lenticule Extraction, FLIVC, or IntraCOR), or other techniques that avoid weakening the cornea with large incisions and deliver less energy to surrounding tissues. The 20/10 (now Technolas) FEMTEC laser has recently been used for incision-less ablation on several hundred human eyes and achieved very successful results for presbyopia,[5] with trials ongoing for myopia and other disorders.
Procedure
There are several necessary preparations in the preoperative period. The operation itself involves creating a thin flap on the eye, folding it to enable remodeling of the tissue beneath with a laser. The flap is repositioned and the eye is left to heal in the postoperative period.
Preoperative
Patients wearing soft contact lenses are usually instructed to stop wearing them 5 to 21 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 have been worn.[6] 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 the locations of corneal tissue to be removed during the operation. The patient typically is prescribed and self-administers an antibiotic beforehand to minimize the risk of infection after the procedure.
Operation
The operation is performed with the patient awake and mobile; however, the patient is sometimes given a mild sedative (such as Valium) and anesthetic eye drops.
LASIK is performed in three steps. The first step is to create a flap of corneal tissue. The second step is remodeling of the cornea underneath the flap with the 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.[7] 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 sometimes be uncomfortable.
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 the adjacent stroma. No burning with heat or actual cutting is required to ablate the tissue. The layers of tissue removed are tens of micrometres 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).
During the second step, the patient's vision will become very blurry once the flap is lifted. They will be able to see only white light surrounding the orange light of the laser, which can lead to mild disorientation.
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. Typical pulses are around 1 millijoule (mJ) of pulse energy in 10 to 20 nanoseconds.[8]
Repositioning 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 care
Patients are usually given a course of antibiotic and anti-inflammatory eye drops. These are continued in the weeks following surgery. Patients are usually told to sleep much more and are also given a darkened pair of shields to protect their eyes from bright lights and protective goggles to prevent rubbing of the eyes when asleep and to reduce dry eyes. They also are required to moisturize the eyes with preservative-free tears and follow directions for prescription drops. Patients should be adequately informed by their surgeons of the importance of proper post-operative care to minimize the risk of complications.
Higher-order aberrations
Higher-order aberrations are visual problems that cannot be diagnosed using a traditional eye exam, which tests only for acuteness of vision. Severe aberrations can cause significant vision impairment. These aberrations include starbursts, ghosting, halos, double vision, and a number of other post-operative complications.
There have always been concerns about LASIK because of its tendency to induce higher-order aberrations. The advancement of the LASIK technology has helped reduce the risk of clinically significant visual impairment after surgery. There is a correlation between pupil size and aberrations.[9] 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, including the appearance of halos surrounding sources of light. There are other currently unknown factors in addition to pupil size that also may lead to higher order aberrations.
In extreme cases in which ideal procedures were not followed by ophthalmologists, and before key advances, some people could suffer debilitating symptoms such as serious loss of contrast sensitivity in poor lighting situations.
Over time, most attention has shifted from other aberrations and centered 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 primarily an issue for major corrections. There are theories that posit that if the lasers were simply programmed to adjust for this tendency, no significant spherical aberration would occur. In eyes with few higher order aberrations, wavefront-optimized LASIK (rather than wavefront-guided LASIK) may well be the future.[citation needed]
Higher order aberrations are measured in micrometers (µm) on the wavescan taken during the pre-op examination, while the smallest beam size of lasers approved by the U.S. Food and Drug Administration 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 small naturally-dilated pupils in dim lighting.
Wavefront-guided LASIK
Wavefront-guided LASIK[10] is a variation of LASIK surgery in which, rather than applying 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 outweigh any benefit from wavefront correction. Therefore, patients expecting so-called "super vision" from such procedures may be disappointed. Still, 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. Currently, there is no research in support of the surgeons' claims.
LASIK surgery results
The surveys determining patient satisfaction with LASIK have found most patients satisfied, with satisfaction range being 92–98 percent.[11][12][13][14] A meta-analysis dated March 2008 performed by the American Society of Cataract and Refractive Surgery over 3,000 peer-reviewed articles published over the past 10 years in clinical journals from around the world, including 19 studies comprising 2,200 patients that looked directly at satisfaction, revealed a 95.4 percent patient satisfaction rate among LASIK patients worldwide. [15]
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.[16] 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.[17] 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[18][19] before issuing guidance for the use of LASIK within the NHS.[20] 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.[21][22]
On October 10, 2006, WebMD reported that statistical analysis revealed that contact lens wear infection risk is greater than the infection risk from LASIK.[23] 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.
Patient dissatisfaction
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 created websites and discussion forums to educate the public about the risks, where prospective and past patients can discuss the surgery. In 1999, Surgical Eyes[24] was founded[25] in New York City[26] by RK patient Ron Link[27] as a resource for patients with complications of LASIK and other refractive surgeries. Other patient-founded websites to assist those with complications are LaserMyEye[28] founded [29] in 2004 and Vision Surgery Rehab[30][31] in 2005.[32] Most experienced and reputable clinics will do a full-dilation medical eye exam prior to surgery and give adequate post-operative patient education care to minimize the risk of a negative outcome.
For best results, Steven C. Schallhorn, an ophthalmologist who oversaw the US Navy's refractive surgery program and whose research partly influenced the Navy's decision to allow its aviators to get LASIK, recommends patients seek out what's called "all-laser Lasik" combined with "wavefront-guided" software.[33][34]
The FDA website on LASIK clearly states: "Before undergoing a refractive procedure, you should carefully weigh the risks and benefits based on your own personal value system, and try to avoid being influenced by friends that have had the procedure or doctors encouraging you to do so."[35] As such, prospective patients still need to fully understand all the potential issues and complications, as satisfaction is directly related to expectation.
The FDA received 140 "negative reports relating to LASIK" for the time period 1998–2006.[36]
The most common complication from refractive surgery is the incidence of "dry eyes." According to an American Journal of Ophthalmology study of March 2006, the incidence rate of dry eyes from LASIK after the six month post operative healing period was 36.36%.[37]. The FDA (Food and Drugs Administration) website states that "dry eyes" may be permanent.[38]
The high incidence of dry eyes necessitates a proper preoperative and post operative evaluation and treatment for dry eyes. There are a number of successful treatments for dry eyes including artificial tears, prescription tears and punctal occlusion. Punctal occlusion is accomplished by placing a collagen plug in the natural drain of the eye. Dry eyes, if left untreated can compromise the visual outcome and result in regression of the effect of LASIK or PRK.
The risk for a patient of suffering from disturbing visual side effects such as halos, double vision (ghosting), loss of contrast sensitivity (foggy vision) and glare after LASIK depends on the degree of ametropia before the laser eye surgery and other risk factors.[39] For this reason, it is important to take into account the individual risk potential of a patient and not just the average probability for all patients.[40] The following are some of the more frequently reported complications of LASIK[41][42]:
Complications due to LASIK have been classified as those that occur due to preoperative, intraoperative, early postoperative, or late postoperative sources:[51]
Intraoperative complications
The incidence of flap complications has been estimated to be 0.244%.[52] 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[53] but rarely lead to permanent visual acuity loss; the incidence of these microkeratome-related complications decreases with increased physician experience.[54][55] According to proponents of such techniques, this risk is further reduced by the use of IntraLasik and other non-microkeratome related approaches, although this is not proven and carries its own set of risks of complications from the IntraLasik procedure.
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. Patients are usually given sleep goggles or eye shields to wear for several nights to prevent them from dislodging the flap in their sleep. 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.[56] 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.[56]
Early postoperative complications
The incidence of diffuse lamellar keratitis (DLK)[57], also known as the Sands of Sahara syndrome, has been estimated at 2.3%.[58] 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%.[58]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)[citation needed] 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),[59] Corneal Collagen Crosslinking with Riboflavin[60] 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.[61] 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.[62] 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% [58](according to a study undertaken in China; thus results may not be generally applicable due to racial and geographic factors).
Late postoperative complications
The incidence of epithelial ingrowth has been estimated at 0.1%.[58]
Glare is another commonly reported complication of those who have had LASIK.[11]
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.[63] 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.[64]
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 "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.
Although there have been improvements in LASIK technology[65][66][67], 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 haziness, halo, or glare, some of which may be irreversible because the LASIK eye surgery procedure is irreversible.
Although the cornea usually is thinner after LASIK, because of the removal of part of the stroma, refractive surgeons strive to maintain the maximum 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.[70][71]
In situ keratomileusis effected at a later age increases the incidence of corneal higher-order wavefront aberrations.[72][73] Conventional eyeglasses do not correct higher order aberrations.
Microfolding has been reported as "an almost unavoidable complication of LASIK" whose "clinical significance appears negligible."[56]
Blepharitis, or inflammation of the eyelids with crusting of the eyelashes, may increase the risk of infection or inflammation of the cornea after LASIK.[citation needed]
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. Although there is currently no method to completely eradicate the need for reading glasses in this group, it may be minimized by performing a variation of the LASIK procedure called "slight monovision." In this procedure, which is performed exactly like distance-vision-correction LASIK, the dominant eye is set for distance vision, while the non-dominant eye is set to the prescription of the patient's reading glasses. This allows the patient to achieve a similar effect as wearing bifocals. The majority of patients tolerate this procedure very well and do not notice any shift between near and distance viewing, although a small portion of the population has trouble adjusting to the monovision effect. This can be tested for several days prior to surgery by wearing contact lenses that mimic the monovision effect.
There are reports of decrease in the number of corneal keratocytes (fibroblasts) after LASIK.[74]
Factors affecting surgery
Typically, the cornea is avascular because it must be transparent to function normally, and its cells absorb 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.
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 2004Wake Forest University study established that heat and humidity affect LASIK surgery results, both during the procedure and in the two weeks before the surgery.[75]
Age considerations
New advances in eyesight corrective surgery are providing consumers greater choices. Patients in their 40s or 50s who are considering LASIK surgery to improve their vision might want to consider to be evaluated for implantable lenses as well. "Early signs of a cataract might argue for surgery and implantation of multifocal lenses instead." [76]
The FDA has approved LASIK for age 18 and over[77]. More importantly the person's eye needs to be stable for two years prior to surgery.
References
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^ ab Tahzib NG, Bootsma SJ, Eggink FA, Nabar VA, Nuijts RM. "Functional outcomes and patient satisfaction after laser in situ keratomileusis for correction of myopia." J Cataract Refract Surg. 2005 Oct;31(10):1943–51. PMID 16338565.
^ Saragoussi D, Saragoussi JJ. "[Lasik, PRK and quality of vision: a study of prognostic factors and a satisfaction survey.]" J Fr Ophtalmol. 2004 Sep;27(7):755-64. PMID 15499272.
^ Bailey MD, Mitchell GL, Dhaliwal DK, Boxer Wachler BS, Zadnik K. "Patient satisfaction and visual symptoms after laser in situ keratomileusis." Ophthalmology. 2003 Jul;110(7):1371–8. PMID 12867394.
^ McGhee CN, Craig JP, Sachdev N, Weed KH, Brown AD. "Functional, psychological, and satisfaction outcomes of laser in situ keratomileusis for high myopia." J Cataract Refract Surg. 2000 Apr;26(4):497–509. PMID 10771222.
^ American Journal of Ophthalmology, Volume 141, Issue 3, March 2006, Pages 438-445,Cintia S. De Paiva, Zhuo Chen, Douglas D. Koch, M. Bowes Hamill, Francis K. Manuel, Sohela S. Hassan, Kirk R. Wilhelmus, Stephen C. Pflugfelder
^ Mirshahi A, Schopfer D, Gerhardt D, Terzi E, Kasper T, Kohnen T. "Incidence of posterior vitreous detachment after laser in situ keratomileusis." Graefes Arch Clin Exp Ophthalmol. 2006 Feb;244(2):149-53. Epub 2005 Jul 26. PMID 16044328.
^ ab Arevalo JF, Mendoza AJ, Velez-Vazquez W, Rodriguez FJ, Rodriguez A, Rosales-Meneses JL, Yepez JB, Ramirez E, Dessouki A, Chan CK, Mittra RA, Ramsay RC, Garcia RA, Ruiz-Moreno JM. "Full-thickness macular hole after LASIK for the correction of myopia." Ophthalmology. 2005 Jul;112(7):1207–12. PMID 15921746.
^ Majmudar, PA. "LASIK Complications."Focal Points: Clinical Modules for Ophthalmologists. American Academy of Ophthalmology. September, 2004.
^ Carrillo C, Chayet AS, Dougherty PJ, Montes M, Magallanes R, Najman J, Fleitman J, Morales A. "Incidence of complications during flap creation in LASIK using the NIDEK MK-2000 microkeratome in 26,600 cases." J Refract Surg. 2005 Sep-Oct;21 (5 Suppl):S655-7. PMID 16212299.
^ abcd Sun L, Liu G, Ren Y, Li J, Hao J, Liu X, Zhang Y. "Efficacy and safety of LASIK in 10,052 eyes of 5081 myopic Chinese patients." J Refract Surg. 2005 Sep-Oct;21 (5 Suppl):S633-5. PMID 16212294.
^ abc Ruiz-Moreno JM, Alio JL. "Incidence of retinal disease following refractive surgery in 9,239 eyes." J Refract Surg. 2003 Sep-Oct;19(5):534-47. PMID 14518742.
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What is LASIK What is LASIK-The parts of the eye. Indicated are the conjunctiva, sclera, choroid, optic nerve, retina, chamber angle, lens, cilary body
