Refractive surgery

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Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency on glasses or contact lenses. This can include various methods of surgical remodeling 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 reduce or cure 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.^[1]

History

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The first experimental studies about refractive surgery were published in 1896 by Lendeer Jans Lans, an ophthalmology teacher in Holland, where he developed a theoretical work proposing penetrating corneal cuts to correct astigmatism. In 1930 the Japanese ophthalmologist Tsutomu Sato made the first practical attempt to perform such surgery in military pilots. He practiced radial cuts in the cornea to correct effects by up to 6 diopters, but this procedure was soon rejected by the medical community because of the high rate of corneal degeneration.

In 1963, in the Barraquer ophthalmologic clinic (Bogotá,Colombia) Ignacio Barraquer developed the first proficient refractive surgery technique called keratomileusis, meaning corneal reshaping (from the Greek Kerato: cornea and Mileusis: to sculpt). Keratomileusis allowed correction of not only myopia but also hyperopia. These early surgeries removed a corneal layer, froze it so it could be manually sculpted in the required shape, and finally reimplanted the layer (Keratomileusis with freezing). While this form of surgery was later improved by Dr. Swinger in 1986 (keratomileusis without freezing)^{[citation needed]}, it was still a relatively imprecise technique.

Meanwhile, experiments in 1970 using a xenon dimer and in 1975 using noble gas halides resulted in the invention of a type of laser called an excimer laser. While excimer lasers were initially used for industrial purposes, in 1980, R. Srinivasan, a scientist of IBM who was using an excimer laser to make microscopic circuits in microchips for informatics equipment, discovered that the excimer could also be used to cut organic tissues with high accuracy without significant thermal damage. The discovery of an effective biological cutting laser, along with the development of computers to control it, allowed new refractive techniques which were previously unavailable. In 1983, scientist Stephen Trokel of Columbia University in collaboration with Srinivasan performed the first Photorefractive Keratectomy (PRK) or keratomileusis in situ (without separation of corneal layer) in Germany. The first patent for LASIK was granted by the US Patent Office to Gholam A. Peyman, MD on June 20, 1989, US Patent #4,840,175, "METHOD FOR MODIFYING CORNEAL CURVATURE", describing the surgical procedure in which a flap is cut in the cornea and pulled back to expose the corneal bed. This exposed surface is then ablated to the desired shape with an excimer laser, following which the flap is replaced. In 1991 Creta University and the Vardinoyannion Eye coined the name "LASIK".

Techniques

Flap procedures

Excimer laser ablation is done under a partial-thickness lamellar corneal flap.

• Automated lamellar keratoplasty (ALK): The surgeon uses an instrument called a microkeratome to cut a thin flap of the corneal tissue. The flap is lifted like a hinged door, targeted tissue is removed from the corneal stroma, again with the microkeratome, and then the flap is replaced.
• Laser Assisted In-Situ Keratomileusis (LASIK): The surgeon uses a microkeratome to cut a flap of the corneal tissue (usually with a thickness of 100-180 micrometres). The flap is lifted like a hinged door, but in contrast to ALK, the targeted tissue is removed from the corneal stroma with an excimer laser. The flap is subsequently replaced. Another method of creating this flap is by using a procedure called IntraLasik, in which a femtosecond laser is used to create the flap. Proponents of this method assert its superiority over "traditional" LASIK, but there have been no conclusive independent studies to prove that this is a true statement.^{[citation needed]}

Surface procedures

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.

• Photorefractive keratectomy (PRK) is an outpatient procedure generally performed with local anesthetic eye drops (as with LASIK/LASEK) . It is a type of refractive surgery which reshapes the cornea by removing microscopic amounts of tissue from the corneal stroma, using a computer-controlled beam of light (excimer laser). The difference from LASIK is that the top layer of the epithelium is removed (and a bandage contact lens is used), so no flap is created. Recovery time is longer with PRK than with LASIK, though the final outcome (after 3 months) is about the same (very good). More recently, customized ablation has been performed with LASIK, LASEK, and PRK.
• Laser Assisted Sub-Epithelium Keratomileusis (LASEK) is a procedure that also changes the shape of the cornea using an excimer laser to ablate the tissue from the corneal stroma, under the corneal epithelium, which is kept mostly intact to act as a natural bandage. The surgeon uses an alcohol solution to loosen then lift a thin layer of the epithelium with a trephine blade (usually with a thickness of 50 micrometres).^[2] During the weeks following LASEK, the epithelium heals, leaving no permanent flap in the cornea. This healing process can involve discomfort comparable to that with PRK.
• EPI-LASIK is a new technique similar to LASEK that uses an epi-keratome (rather than a trephine blade and alcohol), to remove the top layer of the epithelium (usually with thickness of 50 micrometres), which is subsequently replaced. For some people it can provide better results than regular LASEK in that it avoids the possibility of negative effects from the alcohol, and recovery may involve less discomfort.

Corneal incision procedures

• Radial keratotomy (RK) uses spoke-shaped incisions (usually made with a diamond knife) to alter the shape of the cornea and reduce myopia or astigmatism; this technique has now been largely replaced by the other methods (that use excimer laser).

• Arcuate keratotomy (AK) is similar to radial keratotomy, but the incisions on the cornea are done at the periphery of the cornea. Arcuate keratotomy is used to correct astigmatism. Although most incisional procedures are replaced nowadays by Lasik, AK is still used in some special cases (correction of residual astigmatism after a keratoplasty procedure or during cataract surgery).

• Limbal relaxing incisions (LRI) are incisions near the outer edge of the iris, used to correct minor astigmatism (typically less than 2 diopters). This is often performed in conjunction with an Intraocular Lens implantation.

Other procedures

• Thermal keratoplasty is used to correct hyperopia by putting a ring of 8 or 16 small burns surrounding the pupil, and steepen the cornea with a ring of collagen constriction. It can also be used to treat selected types of astigmatism.
• Laser thermal keratoplasty (LTK) is a non-touch thermal keratoplasty performed with a Holmium laser, while conductive keratoplasty (CK) is thermal keratoplasty performed with a high-frequency electric probe. Thermal keratoplasty can also be used to improve presbyopia or reading vision after age 40.
• Intrastromal corneal ring segments (Intacs) are approved by FDA for treatment of low degrees of myopia.
• Lens implantation inside the eye can also be used to change refractive errors.
• Generally refractive surgery can be broadly divided into : corneal surgery, scleral surgery, lens realated surgery( including phakic IOL implantation, clear lens extraction, photophacoreduction and photophacomodulation for correction of pesbyopia)

Expectations

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 to have met the US national norms if 90% of their patients achieve 20/40 vision or better and 65% of their patients achieve 20/20 vision or better, with less than approximately 3% of their refractive surgery patients experiencing a surgery induced complication at six months after surgery, and less than 0.5% being serious complications requiring extensive maintenance or invasive treatment.^[3]

Many people with myopia are able to read comfortably without eyeglasses. Myopes considering refractive surgery are advised that this may be a disadvantage after the age of 40 when the eyes become presbyopic and lose their ability to accommodate or change focus.

Risks

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,^[4] 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,^[5] there is still a small chance for serious problems. These include vision problems such as ghosting, halos, starbursts, double-vision, and dry-eye syndrome.^[6] 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,^[7] with potentially disastrous results if not given prompt medical attention.^[8]

See also

• Orthokeratology - contact lenses worn only at night to reshape the eye.
• Council for Refractive Surgery Quality Assurance, a business league for ophthalmologists.

References

External links

• DJO |Digital Journal of Ophthalmology