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Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease dependency on glasses or contact lenses. This can include various methods of surgical remodelling of the cornea or cataract surgery. The most common methods today use excimer lasers to reshape curvature of the cornea. Successful refractive eye surgery can help to reduce common vision disorders such as myopia, hyperopia and astigmatism.
According to surveys of members of the American Society of Cataract and Refractive Surgery, approximately 948,266 refractive surgery procedures were performed in the United States during 2004 and 928,737 in 2005.
Additional recommended knowledge
The first experimental studies about refractive surgery were developed by Lendeer Jans Lans, an ophthalmology teacher in Holland, 1896 where he published a theoretic work proposing penetrating corneal cuts to correct astigmatism. In 1930 the Japanese ophthalmologist Sato[specify] made the first practical attempt to perform such surgery in military pilots. He practiced radial cuts in the cornea to correct effects up to 6 diopters, but this procedure was soon rejected by the medical community because the high rate of corneal degeneration. In 1963, in the Barraquer ophthalmologic clinic (Bogotá,Colombia) Ignacio Barraquer developed the first proficient technique to refractive surgery, called keratomileusis (from the Greek Kerato: cornea and Mileusis: to sculpt) meaning corneal reshaping. Keratomileusis allowed to correct not only myopia but also hyperopia. The early surgeries were made removing a corneal layer, freezing it so it could be manually sculpted in the required shape and finally reimplant the layer (Keratomileusis with freezing). In 1986 Dr Swinger improved the surgery (keratomileusis without freezing) but it was still a slightly imprecise technique. In 1958 Arthur Schawlow and Townes, from Bell laboratories published their theory of stimuled emission of shorter length waves, included light, which gave place to the development of Laser. In 1975 experiments with laser using a mix of argon and fluor ended with the invention of the Excimer. This Laser was used with industrial purposes. In 1980, R. Srinivasan, a scientist of IBM who was using the Excimer to make microscopic circuits in microchips for informatic quipments, discovered that the Excimer could be used also to cut organic tissues with high accuracy without significant thermal damage. In 1983 Stephen Trokel, scientist of Columbia University in collaboration with Srinivasan performed the Photorefractive Keratectomy (PRK) or keratomileusis in situ (without separation of corneal layer) which was more technically exact, but the patients reported it to be very uncomfortable. Also a delay in the healing was observed. The first PRK was performed in Germany. In 1991 the Creta University and the Vardinoyannion Eye developed Lasik that worked with the same principles, but removing first a lens shaped piece of the outer layer of the cornea, sculpting the inner layer and relocating the piece to cover, which allows a faster healing, without discomfort. However, there exists debate over the stability of the healing with the corneal flap. Current PRK procedures involve the removal of the corneal layer with an alcohol based solution for the corrective procedure, and then allowing the layer to regenerate. However, this is somewhat painful for the patient following the procedure and takes longer for visual acuity to stabilize.
Excimer laser ablation is done under a partial-thickness lamellar corneal flap.
The excimer laser is used to ablate the most anterior portion of the corneal stroma. These procedures do not require a partial thickness cut into the stroma. Surface ablation methods differ only in the way the epithelial layer is handled.
Corneal incision procedures
The Council for Refractive Surgery Quality Assurance, an independent, nonprofit, patient/consumer health organization that provides information about refractive surgery and certifies LASIK surgeons, considers surgeons with results of 90% of patients achieving 20/40 or better and 65% achieving 20/20 or better with limited approximately 3% of refractive surgery patients experiencing a surgery induced complication at six months after surgery, with 0.5% being serious complications requiring extensive maintenance or invasive treatment as meeting the US national norms.
Many people with myopia are able to read comfortably without eyeglasses. Myopes considering refractive surgery are advised that this may be an advantage after the age of 40 when the eyes become presbyopic and lose their ability to accommodate or change focus.
While refractive surgery is becoming more affordable and safe, it may not be recommended for everybody. Patients that have medical conditions such as glaucoma or diabetes, uncontrolled vascular disease, autoimmune disease, pregnant women or people with certain eye diseases involving the cornea or retina, are not good candidates for refractive surgery. Keratoconus, a progressive thinning of the cornea, is a common corneal disorder. It is believed that additional thinning of the cornea via refractive surgery may contribute to advancement of the disease  , that may lead to the need for a corneal transplant. Therefore, keratoconus is a contraindication to refractive surgery. Corneal topography, pachymetry and, more recently, Pentacam exams are used to screen for abnormal corneas. Furthermore, some people's eye shape may not permit effective refractive surgery without removing excessive amounts of corneal tissue. Those considering laser eye surgery should have a full eye examination.
Although the risk of complications is decreasing compared to the early days of Refractive surgery,  there is still a small chance for problems sometimes serious. These include vision problems such as ghosting, halos, starbursts, double-vision, and dry-eye syndrome.  With procedures that create a permanent flap in the cornea (such as LASIK), there is also the possibility of accidental traumatic flap displacement years after the surgery,  with potentially disastrous results if not given prompt medical attention. 
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Refractive_surgery". A list of authors is available in Wikipedia.|