Refractive surgery
Template:Globalize/USA Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease dependency on glasses or contact lenses. 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.[1]
Techniques
Flap procedures
Consists in cutting a flap in the cornea in order to access the tissue underneath.
- Automated lamellar keratoplasty (ALK)
- Laser Assisted In-Situ Keratomileusis (LASIK) is the most commonly performed refractive surgery procedure as of 2007. Surface treatment ablation has gained a renewed interest in recent years as evidence of good outcomes have been shown. LASIK is performed for a wide range of nearsightedness. The surgeon uses an instrument called a microkeratome to cut a flap of the corneal tissue (usually with about 160 micra in thickness). He then opens the flap like a hinged door, removes the targeted tissue in the corneal stroma beneath it with the excimer laser, and then replaces the flap. Some variations do not use a microkeratome but cut the flap with a laser (intralase).
- Laser Assisted Sub-Epithelium Keratomileusis (LASEK) is a procedure that 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 almost intact to act as a natural bandage.
- 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 cornea.
Photoablation procedures
- Photorefractive keratectomy (PRK) is an outpatient procedure generally performed with local anesthetic eye drops (as LASIK) . It is a type of refractive surgery which reshapes the cornea by destroying microscopic amounts of tissue from corneal stroma, using the computer-controlled beam of light (an excimer laser). The difference from LASIK is that all the epithelium is removed (and a bandage contact lens must be used). Recovery time is much longer with PRK than with LASIK, though the final outcome (after 3 months) is about the same (very good). More recently, customized ablation have been performed either with LASIK or PRK.
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).
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 no-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.
- Intra-Stromal corneal rings (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.
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 with results of 90% of patients achieving 20/40 or better and 50% achieving 20/20 or better with limited complication rates as meeting national norms.[2]
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.
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 [1], that may lead to the need for a corneal transplant. Therefore, keratoconus is a contraindication to refractive surgery. Corneal topography, paquimetry 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.
References
See also
- Orthokeratology - contact lenses worn only at night to reshape the eye.