LASIK or Lasik ( in situ laser assisted keratomileusis ), commonly referred to as laser eye surgery or correction laser vision , is a type of refractive surgery for correction of myopia, hyperopia, and astigmatism. LASIK surgery is performed by optometrists using a laser or microkeratome to reshape the cornea to enhance visual acuity. For most people, LASIK provides a durable alternative to glasses or contact lenses.
LASIK is most similar to other surgical corrective procedures, photorefractive keratectomy (PRK), and LASEK. All represent the progress of radial keratotomy in the treatment of vision errors bias surgery. For patients with moderate or high myopia or thin corneas that can not be treated with LASIK and PRK, intraocular phakic lenses are an alternative. By 2018, nearly 10 million LASIK procedures have been performed in the United States and, by 2016, more than 40 million have been conducted worldwide since 1991. However, this procedure seems to be a declining option for many people in the United States, dropping more than 50 percent, from about 1.5 million operations in 2007 to 604,000 in 2015, according to Eye Markets eye data sources.
Video LASIK
Effectiveness
In 2006, the National Health Service and Clinical Excellence (NICE) of the UK National Health Agency considers evidence of the effectiveness and potential risks of laser surgery saying "current evidence suggests that photorefractive (laser) surgery for safe and efficacious correction of errors is safe for use in patients The physician performing a photorefractive (laser) surgery for correction of refractive error should ensure that the patient understands the potential benefits and risks of the procedure, new vision disorders, corneal infections and fold complications.These risks should be weighed against those who wear glasses or lenses contact. "The FDA reported" The safety and effectiveness of refractive procedures has not been determined in patients with multiple diseases. "
Satisfaction
The LASIK surgical survey found patient satisfaction levels between 92 and 98 percent. In March 2008, the American Society of Cataract and Refractive Surgery published a patient satisfaction meta-analysis of more than 3,000 articles reviewed from an international clinical journal. Data from the previous 10 years revealed a 95.4 percent patient satisfaction rate among LASIK patients.
Dissatisfaction
Some people with poor results from the LASIK surgical procedure report a significant decrease in the quality of life due to vision problems or physical pain associated with surgery. A small percentage of patients may need to undergo other surgery because their condition is too corrected or less corrected. Some patients need to wear contact lenses or glasses even after treatment.
The most common reason for dissatisfaction in LASIK patients is severe chronic dry eyes. Independent research showed 95% of patients had dry eyes in the postoperative period. This amount has been reported up to 60% after one month. Symptoms begin to improve in most patients within 6 to 12 months after surgery. However, 30% of post-LASIK referral to a tertiary ophthalmic treatment center has been shown to be due to chronic dry eye.
Morris Waxler, a former FDA official involved in LASIK approval, later criticized his widespread use. In 2010, Waxler created a media view and claimed that the procedure had a failure rate of over 50%. The FDA responds that Waxler's information "is filled with false statements, false quotes" and "mischaracterization of results".
A JAMA 2016 study showed that the prevalence of complications from LASIK was higher than indicated, with research showing many patients ending with glare, halos or other visual symptoms. LASIK-related observations of complications have been recorded on the internet.
Presbyopia
A type of LASIK, known as presbyLasik, can be used in presbyopia. The results, however, are more variable and some people experience a decrease in visual acuity.
Maps LASIK
Risk
Higher order deviations
High-order deviations are visual problems that require special testing for diagnosis and are not corrected with ordinary glasses (glasses). These irregularities include 'starbursts', 'ghosting', 'halos' and others. Some patients describe the postoperative symptoms and associate them with LASIK techniques including the formation of flaps and tissue ablation.
Advances in LASIK technology have reduced the risk of vision impairment that is clinically significant after surgery. There is a correlation between the pupil size and the deviation. This correlation may be due to an irregularity of the corneal tissue between the untouched portion of the cornea and the re-formed part. Daytime post-LASIK vision is optimal, because the pupil size is smaller than the LASIK flap. However, at night, the pupils may enlarge as the light passes over the edge of the LASIK flap, which raises the aberration. LASIK and PRK can cause ball irregularities if the laser is less corrected as it moves out of the center of the treatment zone, especially when major corrections are made.
Others propose that high-order deviations are present before the operation. They can be measured in micrometers (Âμm) while the smallest laser-light size approved by the FDA is about 1000 times larger, at 0.65 mm. In situ elderly keratomileusis increases the incidence of higher initial wave aberrations in the cornea. These factors indicate the importance of careful patient selection for LASIK treatment.
Dry eyes
95% of patients report dry eye symptoms after LASIK Although usually temporary can develop into chronic and severe dry eye syndrome. Quality of life can be strongly affected by dry eye syndrome.
Underlying conditions with dry eyes such as SjÃÆ'¶gren syndrome are considered contraindicated for Lasik.
Treatments include artificial tears, prescription tears and faint occlusion. Punctal occlusion is achieved by placing collagen or silicon plugs in the tear ducts, which usually drain fluid from the eye. Some patients complain of persistent dry eye symptoms even though such treatments and dry eye symptoms may be permanent.
Halos
Some post-LASIK patients see halos and starbursts around bright lights at night. At night, the pupils may dilate larger than the flap that leads to the edge of the flap or stromal changes causing light visual distortion that does not occur during the day when the pupil is smaller. The eyes can be examined for large pre-operative pupils and the risk of these symptoms is assessed.
Complications due to LASIK have been classified as occurring due to preoperative, intraoperative, postoperative, or postoperative post-operative sources: According to the National Health Services UK complications occur in less than 5% of cases.
Other complications
- Flap complications - The incidence of flap complications is about 0.244%. Flap complications (such as flaps or folds in flaps requiring repositioning, diffuse diffuse keratitis, and epithelial ingrowth) are common in lamellar corneal surgery but rarely cause permanent visual loss of visual acuity. The incidence of complications associated with microkeratome decreases with increasing physician experience.
- Slipping Slip - is a corneal flap that is detached from the rest of the cornea. This possibility is greatest immediately after surgery, so patients are usually advised to go home and sleep to let the flap stick and heal. Patients are usually given sleeping goggles or eye protection to wear for a few nights to prevent them from releasing the cover in their sleep. Short operating times can reduce the likelihood of these complications, because there is less time to dry.
- Flap interface particles - are findings whose clinical significance has not yet been determined. Particles of various sizes and reflections are clinically seen in about 38.7% of the eyes examined through biomicroscopy gap lamps and in 100% of the eyes examined by confocal microscopy.
- Diffuse diffuse keratitis Ã, - an inflammatory process involving the accumulation of white blood cells at the interface between the LASIK corneal flap and the underlying stroma. It is known colloquially as the "sand of Sahara syndrome" because upon examination of the slit lamp, the inflammatory infiltrate looks similar to the sand wave. The USAeyes organization reported an incidence of 2.3% after LASIK. It is most often treated with steroid eye drops. Sometimes it is necessary for the ophthalmologist to lift the flap and manually remove the accumulated cell. DLK has not been reported with photorefractive keratectomy due to absence of flap creation.
- Infection - the incidence of responsive infections to treatment has been estimated at 0.4%.
- Post-LASIK corneal abnormalities - a condition in which the cornea begins to swell forward at varying times after LASIK, causing irregular astigmatism. its condition is similar to keratoconus.
- Subconjunctival hemorrhageÃ, - A report shows subconjunctival bleeding events have been estimated at 10.5%.
- Corneal scar tissue - or a permanent problem with a corneal shape making it impossible to wear contact lenses.
- Plant epithelium - estimated 0.1%.
- Dislocation of traumatic flap - A further traumatic flap dislocation case has been reported for up to seven years after LASIK.
- Retinal detachment: estimated at 0.36 percent.
- Choroidal Neovascularization: estimated at 0.33 percent.
- Uveitis: estimated at 0.18 percent. For climbers - Although the cornea is usually thinner after LASIK, due to removal of parts of the stroma, refractive surgeons try to maintain maximum thickness to avoid structurally weakening the cornea. Decreasing atmospheric pressure at higher altitudes has not proven to be very harmful to the eyes of LASIK patients. However, some mountain climbers have experienced a nearsighted shift at extreme altitudes.
- End of postoperative complications - Much of the evidence about the possibility of long-term complications has not yet been established and may change as advances in operator experience, instruments and techniques.
- The best potential loss of vision can occur a year after surgery regardless of the use of glasses.
- Eye floaters - ocular mechanical pressure made by LASIK has the potential to damage the vitreous, retina, and macula that cause floaters as a result.
FDA position
In October 2009, the FDA, the National Eye Institute (NEI), and the Department of Defense (DoD) launched the LASIK Quality of Life Collaboration (LQOLCP) Project to help better understand the potential risks of severe problems that LASIK can cause in response to widespread problems by the patient after LASIK laser eye surgery. The project examined the results reported by patients with LASIK (PROWL). The project consists of three phases: the pilot phase, phase I, phase II (PROWL-1) and phase III (PROWL-2). The last two phases are completed in 2014.
Hasil LASIK Quality of Life Study diterbitkan pada bulan Oktober 2014.
Director of the FDA of the Ophthalmic Devices Division, said about the LASIK study "Given the large number of patients undergoing LASIK every year, dissatisfaction and paralyzing symptoms can occur in a large number of patients". Also in 2014, the FDA publishes an article highlighting risks and a list of factors and conditions that should be considered when choosing a doctor for their refractive surgery.
Process
Planning and analysis of corneal reshaping techniques such as LASIK has been standardized by the American National Standards Institute, an approach based on the Alpins astigmatism analysis method. The FDA website at LASIK stated,
- "Before undergoing a refractive procedure, you should carefully consider risks and rewards based on your own personal value system, and try not to be influenced by friends who have undergone a procedure or a doctor who encourages you to do so. "
This procedure involves making a thin flap on the eye, folding it to allow remodeling of the tissue below with the laser and repositioning the flap.
Preoperative procedures
Contact lens
Patients who wear soft contact lenses are instructed to stop wearing it 5 to 21 days before surgery. One industry body recommends that patients who wear hard contact lenses should stop wearing them for at least six weeks plus six weeks for every three years of hard contact that has been used. The cornea is avascular because it must be transparently functioning normally. Its cells absorb oxygen from the tear film. Thus, low-oxygen contact lenses can reduce the absorption of corneal oxygen, sometimes resulting in neovascularization of the cornea - the growth of blood vessels into the cornea. This causes a slight extension of the duration of inflammation and healing time and some pain during surgery, due to greater bleeding. Although some contact lenses (especially RGP lenses and silicone modern silicone hydrogels) are made of materials with greater oxygen permeability that help reduce the risk of corneal neovascularization, patients considering LASIK are warned to avoid wearing their contact lenses excessively.
Pre-operative and educational checks
In the United States, the FDA has approved LASIK for ages 18 and over. More importantly, a patient's eye prescription should be stable at least one year before surgery. Patients can be examined with pupil dilatation and education provided before the procedure. Before surgery, the patient's cornea is examined with a pachymeter to determine its thickness, and with topography, or topographic corneal engine, to measure its surface contour. Using a low power laser, a topography creates a topographic map of the cornea. This procedure is contraindicated if topographers find difficulties such as keratoconus The preparation process also detects astigmatism and other irregularities in the form of the cornea. Using this information, the surgeon calculates the number and location of the corneal tissue to be removed. Patients prescribed and self-administrers of antibiotics previously to minimize the risk of infection after the procedure and are sometimes offered oral sedative acting briefly as pre-medication. Prior to the procedure, anesthetic eye drops were implanted. Factors that may rule out LASIK for some patients include large pupils, thin corneas and very dry eyes.
Operating procedure
Flap creation
A soft corneal suction ring is applied to the eye, holding the eye in its 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, harmless side effects that disappear within weeks. Increased suction causes temporary vision dimming in the treated eye. After the eyes can not move, the flap is made by cutting the corneal epithelium and the Bowman lining. This process is achieved by mechanical microkeratome using a metal knife, or a femtosecond laser that creates a series of small, tightly packed bubbles inside the cornea. Hinges are left at one end of this flap. The flap is folded backwards, exposing the stroma, the center of the cornea. The process of lifting and re-folding the flap is sometimes uncomfortable.
Laser remodeling
The second step of this procedure uses an excimer laser (193Ã, nm) to overhaul the corneal stroma. The laser evaporates the tissue in a smoothly controlled fashion without damaging the adjacent stroma. No burning with heat or cutting is actually needed to erode the network. The tissue layer that is released is tens of micrometers thick.
Performing laser ablations on the deeper stroma cornea provides faster visual recovery and less pain than the previous technique, photorefractive keratectomy (PRK).
During the second step, the patient's vision becomes opaque, once the flap is removed. They will be able to see only the white light that surrounds the orange light of the laser, which can cause mild disorientation. The excimer laser uses an eye-tracking system that follows the patient's eye position up to 4,000 times per second, directing the laser pulse for proper placement within the maintenance zone. Typical pulses are about 1 millijoule (mJ) of pulse energy in 10 to 20 nanoseconds.
Re-positioning flap
After the laser reshapes the stroma layer, the LASIK flap is carefully repositioned over the area of ​​care by the surgeon and checks for air bubbles, dirt, and fits in the eye. The flap remains in position by natural adhesion until the healing is complete.
Postoperative care
Patients are usually given antibiotic eye drops and anti-inflammatory drugs. This continued in the weeks following surgery. Patients are instructed to rest and are given sunglasses to protect their eyes from bright light and sometimes protective eyewear to prevent rubbing the eyes while asleep and to reduce dry eyes. They are also required to moisturize the eyes with preservative-free tears and follow the instructions for prescription drops. Sometimes after a contact lens attachment procedure is placed to aid healing, and is usually removed after 3-4 days. Patients should be adequately informed by their surgeons about the importance of appropriate postoperative care to minimize the risk of complications.
Wavefront-guided
When treating patients with pre-existing astigmatism, wavefront-guided LASIK lasers are designed to treat regular astigmatism that is externally determined by corneal topography. In patients who have internally induced astigmatism elements, therefore, correction of wavefront-guided astigmatism may leave behind regular astigmatism (cross-cylinder effect). If the patient has irregular astigmatism, the wavefront-guided approach can leave behind regular and irregular astigmatism behind. This can result in less than optimal visual acuity compared to the wavefront guided approach combined with vector planning, as demonstrated in the 2008 study. Thus, vector planning offers better alignment between corneal astigmatism and laser treatment, and leaves little astigmatism in back on the cornea, which is advantageous whether irregular astigmatism coexist or not.
The "residual" astigmatism after pure laser correction of surface guided can be calculated first, and is called ocular ocular astigmatism (ORA). ORA is the calculation of astigmatism because of the noncorneal (internal) optical surface. The pure refraction-based approach represented by the wavefront analysis is actually a conflict with the experience of corneal surgery developed over the years.
The path to "super vision" may thus require a more specific approach to corneal astigmatism than is usually attempted, and any remaining astigmatism must be orderly (irregularly opposed), which is the basic principle of vector planning that is ignored by pure wavefront. guided care plan. This is confirmed by the 2008 study mentioned above, which found a greater decrease in corneal astigmatism and better visual results under mesopic conditions using wavefront technology combined with vector analysis rather than using wavefront technology alone, and also found high-level deviations that equivalent (see below). Vector planning also proved useful in patients with keratoconus.
No good data can be found that compares the percentage of LASIK procedures that use wavefront guidance versus percentages that do not, or percentage of refractive surgeons who have one way or another preference. Wavefront technology continues to be positioned as a "progress" in LASIK with putative advantages; however, it is clear that not all LASIK procedures are performed with wavefront guidance.
However, the surgeon claims the patient is generally more satisfied with this technique than the previous method, especially regarding the low incidence of "halos," the visual artifacts caused by spherical aberrations caused by previous methods. A meta-analysis of eight trials showed a lower incidence of higher sequence deviations in patients with wavefront-guided LASIK compared with non-wavefront-guided LASIK. Based on their experience, the United States Air Force has described WFG-Lasik as a "superior outcome".
Topographic help
Topographically assisted LASIK is intended to be an advancement in precision and reduce the side effects of night vision. The first topographic aids receive FDA approval September 13, 2013.
History
Initial Barraquer job
In the 1950s, microkeratome and keratomileusis techniques were developed in BogotÃÆ'¡, Colombia, by the Spanish eye doctor Jose Barraquer. At his clinic, he will cut a thin (one hundredth thick) flap in the cornea to change his shape. Barraquer also investigated how much cornea should be left unchanged to provide long-term stable results. This work was followed by Russian scientist Svyatoslav Fyodorov, who developed radial keratotomy (RK) in 1970 and designed the first posterior rear space contact lens (intraocular phakic lens) in the 1980s.
Refractive laser operation
In 1980, Rangaswamy Srinivasan, in the IBM Research laboratory, found that ultraviolet excimer lasers can form live tissue, with precision and without thermal damage to the surrounding area. He named the phenomenon of "photo-decomposition ablative" (APD). Five years later, in 1985, Steven Trokel at Edward S. Harkness Eye Institute, Columbia University in New York City, published his work using an excimer laser in radial keratotomy. He wrote,
- "Central aberration of the cornea obtained with a diamond radial knife cut has been duplicated by a radial laser incision on 18 humanized eyes that are cultivated.The incision, made by 193 nm of distant ultraviolet radiation emitted by an excimer laser, produces the cornea. leveling from 0.12 to 5.35 diopters, both corneal incision depth and central corneal flattening rate correlated with applied laser energy Histopathology revealed a very fine edge of a laser incision. "
Together with his colleagues, Charles Munnerlyn and Terry Clapham, Trokel founded VISX USA inc. Marguerite B. MacDonald MD performed the first human eye refractory eye surgery in 1989.
Patent
A number of patents have been issued for several techniques related to LASIK. Stuart I. Brown and Josef F. Bille filed a patent on a surgical laser in 1988. Samuel E. Blum, Rangaswamy Srinivasan and James Wynne applied for a patent on ultraviolet excimer laser, in 1982, issued in 1988. In 1989, Gholam A Peyman is granted a US patent for using an excimer laser to modify corneal curvature. Past,
- "A method and apparatus for modifying the corneal curvature of life through the use of excimer lasers.The live cornea has a thin layer removed from it, leaving an open internal surface on it, then a surface or thin layer is exposed to laser light along the pattern which has been determined to obscure the desired portion The thin layer is then replaced to the surface. Eliminating the center area of ​​the surface or thin layer makes the cornea less curved, while ablating the annular area is distant from the center of the surface or the layer makes the cornea more curved The predetermined pattern is formed using a diaphragm variable, variable size rotating hole, moving mirror or fiber optic cable moving through which the laser beam is directed toward the exposed internal surface or a thin layer is removed. "
Patents relating to so-called LASIK technology and broad-beam PRK were granted to US companies including Visx and Summit during 1990-1995 based on US patents issued to IBM (1983) which claimed the use of UV lasers for organic tissue ablation.
Deployment in US.
LASIK Engineering is implemented in the US after its successful implementation elsewhere. The Food and Drug Administration (FDA) started an excimer laser test in 1989. The first company to receive FDA approval for using excimer lasers for photo-refractive keratectomy was Peak Technology (founder and CEO, Dr. David Muller). In 1992, under the direction of the FDA, Greek ophthalmologist Ioannis Pallikaris introduced LASIK to ten VISX centers. In 1998, "Kremer Excimer Laser", serial number KEA 940202, received FDA approval for single use to perform LASIK. Furthermore, Summit Technology is the first company to receive FDA approval to mass produce and distribute excimer lasers. VISX and other companies follow.
Pallikaris recommends corneal flap can be generated by microkeratome before the implementation of the CRC with laser excimer. The addition of flaps to the CRP is known as LASIK.
Further research
Since 1991, there have been further developments such as lasers faster; a larger spot area; incision of smokeless flap; intraoperative corneal cronymetry; and "wavefront-optimized" and "wavefront-guided" techniques. The purpose of refractive surgery is to permanently avoid the cornea with an incision and provide less energy to the surrounding tissue.
Experimental techniques
- "plain" LASIK: LASEK, Epi-LASIK,
- Keratomileusis Sub-Bowman (LASIK cover thin),
- PRK guided by Wavefront,
- advanced intraocular lenses.
- Femtosecond laser intrastromal vision correction: using all-femtosecond correction, for example, Femtosecond Lenticule EXtraction, FLIVC, or IntraCOR),
- Keraflex: thermobiochemical solution that has received CE Mark for refractive correction. and in European clinical trials for correction of myopia and keratoconus.
- FEMTEC laser Technolas: for IntraCOR ablation without incisions for presbyopia, with ongoing trials for myopia and other conditions.
- LASIK with the IntraLase femtosecond laser: a preliminary trial comparing Ã,  «LASIK with microkeratoma for myopia correction showed no significant difference in safety or efficacy. However, femtosecond lasers have a potential advantage in predictability, although these findings are not significant  ».
Comparison with photorefractive keratectomy
A systematic review comparing PRK and LASIK concludes that LASIK has a shorter recovery time and less pain. Two techniques after a period of one year have similar results.
A systematic review of 2017 uncovered uncertainty in visual acuity, but found that in one study, those who received a PRK were less likely to achieve biased errors, and tended to experience less correction than compared to LASIK.
References
External links
- What is LASIK? - Food and Drug Administration
- Laser Eye Surgery - National Library of Medicine United States
- Ectasia After LASIK in EyeWiki
Source of the article : Wikipedia
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