Process
The planning and analysis of corneal reshaping techniques such as LASIK have been standardized by the American National Standards Institute, an approach based on the Alpins method of astigmatism analysis. The FDA website on LASIK 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."[51]
The procedure involves creating a thin flap on the eye, folding it to enable remodeling of the tissue beneath with a laser and repositioning the flap.
Preoperative procedures
Contact lenses
Patients wearing soft contact lenses are 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. The cornea is avascular because it must be transparent to function normally. 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.
Pre-operative examination and education
In the United States, the FDA has approved LASIK for age 18 and over. More importantly the patient"s eye prescription should be stable for at least one year prior to surgery. The patient may be examined with pupillary dilation and education given prior to the procedure. Before the surgery, the patient"s corneas are examined with a pachymeter to determine their thickness, and with a topographer, or corneal topography machine,[1] to measure their surface contour. Using low-power lasers, a topographer creates a topographic map of the cornea. The procedure is contraindicated if the topographer finds difficulties such as keratoconus[1] The preparatory process also detects astigmatism and other irregularities in the shape of the cornea. Using this information, the surgeon calculates the amount and the location of corneal tissue to be removed. The patient is prescribed and self-administers an antibiotic beforehand to minimize the risk of infection after the procedure and is sometimes offered a short acting oral sedative medication as a pre-medication. Prior to the procedure, anaesthetic eye drops are instilled. Factors that may rule out LASIK for some patients include large pupils, thin corneas and extremely dry eyes.[52]
Dry eyes
95% of patients report dry eye symptoms after LASIK[25] Although it is usually temporary it can develop into chronic and severe dry eye syndrome. Quality of life can be severely affected by dry eye syndrome.[26]
Underlying conditions with dry eye such as Sjögren"s syndrome are considered contraindications to Lasik.[27]
Treatments include artificial tears, prescription tears and punctal occlusion. Punctal occlusion is accomplished by placing a collagen or silicone plug in the tear duct, which normally drains fluid from the eye. Some patients complain of ongoing dry eye symptoms despite such treatments and dry eye symptoms may be permanent.[28]
Halos
Some post-LASIK patients see halos and starbursts around bright lights at night. At night, the pupil may dilate to be larger than the flap leading to the edge of the flap or stromal changes causing visual distortion of light that does not occur during the day when the pupil is smaller. The eyes can be examined for large pupils pre-operatively and the risk of this symptom assessed.
Complications due to LASIK have been classified as those that occur due to preoperative, intraoperative, early postoperative, or late postoperative sources:[29] According to the UK National Health Service complications occur in fewer than 5% of cases.[25]
Other complications
- Flap complications – The incidence of flap complications is about 0.244%.[30] 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[31] but rarely lead to permanent loss of visual acuity. The incidence of these microkeratome-related complications decreases with increased physician experience.[32]
- Slipped flap – is a corneal flap that detaches from the rest of the cornea. The chances of this are greatest immediately after surgery, so patients typically are advised to go home and sleep to let the flap adhere and 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 short operation time may decrease the chance of this complication, as there is less time for the flap to dry.[citation needed]
- Flap interface particles – are a finding whose clinical significance is undetermined.[33] Particles of various sizes and reflectivity are clinically visible in about 38.7% of eyes examined via slit lamp biomicroscopy and in 100% of eyes examined by confocal microscopy.[33]
information was "filled with false statements, incorrect citations" and "mischaracterization of results".[17]
A 2016 JAMA study indicates that the prevalence of complications from LASIK are higher than indicated, with the study indicating many patients wind up with glare, halos or other visual symptoms.[18]
Presbyopia
A type of LASIK, known as presbyLasik, may be used in presbyopia. Results are, however, more variable and some people have a decrease in visual acuity.[19]
Risks
Higher-order aberrations
Higher-order aberrations are visual problems that require special testing for diagnosis and are not corrected with normal spectacles (eyeglasses). These aberrations include "starbursts", "ghosting", "halos" and others.[20] Some patients describe these symptoms post-operatively and associate them with the LASIK technique including the formation of the flap and the tissue ablation.[21]
The advancement of the LASIK technology has reduced the risk of clinically significant visual impairment after surgery.[citation needed] There is a correlation between pupil size and aberrations. This correlation may be the result of irregularity in the corneal tissue between the untouched part of the cornea and the reshaped part. Daytime post-LASIK vision is optimal, since the pupil size is smaller than the LASIK flap. However, at night, the pupil may dilate such that light passes through the edge of the LASIK flap, which gives rise to aberrations. LASIK and PRK may induce spherical aberration if the laser under-corrects as it moves outward from the centre of the treatment zone, especially when major corrections are made.[citation needed]
Others propose that higher-order aberrations are present preoperatively.[22] They can be measured in micrometers (µm) whereas the smallest laser beam size approved by the FDA is about 1000 times larger, at 0.65 mm. In situ keratomileusis effected at a later age increases the incidence of corneal higher-order wavefront aberrations.[23][24] These factors demonstrate the importance of careful patient selection for LASIK treatment.
Effectiveness
In 2006, the British National Health Service"s National Institute for Health and Clinical Excellence (NICE) considered evidence of the effectiveness and the potential risks of the laser surgery stating "current evidence suggests that photorefractive (laser) surgery for the correction of refractive errors is safe and efficacious for use in appropriately selected patients. Clinicians undertaking photorefractive (laser) surgery for the correction of refractive errors should ensure that patients understand the benefits and potential risks of the procedure. Risks include failure to achieve the expected improvement in unaided vision, development of new visual disturbances, corneal infection and flap complications. These risks should be weighed against those of wearing spectacles or contact lenses."[7] The FDA reports "The safety and effectiveness of refractive procedures has not been determined in patients with some diseases."[8]
Satisfaction
Surveys of LASIK surgery find rates of patient satisfaction between 92 and 98 percent.[9][10][11] In March 2008, the American Society of Cataract and Refractive Surgery published a patient satisfaction meta-analysis of over 3,000 peer-reviewed articles from international clinical journals. Data from the prior 10 years revealed a 95.4 percent patient satisfaction rate among LASIK patients.[12]
Dissatisfaction
Some people with poor outcomes from LASIK surgical procedures report a significantly reduced quality of life because of vision problems or physical pain associated with the surgery. A small percentage of patients may need to have another surgery because their condition is over-corrected or under-corrected. Some patients need to wear contact lenses or glasses even after treatment.[13]
The most common reason for dissatisfaction in LASIK patients is chronic severe dry eye. Independent research indicates 95% of patients experience dry eye in the inital post-operative period. This number has been reported to up to 60% after one month. Symptoms begin to improve in the vast majority of patients in the 6 to 12 months following the surgery.[14] However, 30% of post-LASIK referrals to tertiary opthamology care centers have been shown to be due to chronic dry eye.[15] [16]
Morris Waxler, a former FDA official who was involved in the approval of LASIK, has subsequently criticized its widespread use. In 2010, Waxler made media appearances and claimed that the procedure had a failure rate greater than 50%. The FDA responded that Waxler"s
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LASIK surgery using an excimer laser at US National Naval Medical Center Bethesda |
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LASIK or Lasik (laser-assisted in situ keratomileusis), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and astigmatism. The LASIK surgery is performed by an ophthalmologist who uses a laser or microkeratome to reshape the eye"s cornea in order to improve visual acuity.[1] For most people, LASIK provides a long-lasting alternative to eyeglasses or contact lenses.[2]
LASIK is most similar to another surgical corrective procedure, photorefractive keratectomy (PRK), and LASEK. All represent advances over radial keratotomy in the surgical treatment of refractive errors of vision. For patients with moderate to high myopia or thin corneas which cannot be treated with LASIK and PRK, the phakic intraocular lens is an alternative.[3][4] As of 2011, over 11 million LASIK procedures had been performed in the United States[5] and as of 2009 over 28 million have been performed worldwide.[6]
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