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Refractive Surgery
Refractive Surgery
 
Myopia
Hyperopia
Astigmatism

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.

Techniques

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

.

A  corneal flap usually 100 to 180 microns is made by an instrument called a microkeratome or more recently also by a femtosecond Laser. As of now both methods give comparable results. The flap is lifted like a hinged door. The following is then done.

Laser Assisted In-Situ Keratomileusis (LASIK):  The targeted tissue , calculated based on the error to be corrected, is removed from the corneal stroma with an excimer laser. The flap is subsequently replaced.

Surface procedures
In these techniques, no partial thickness flap is made. Several methods can be used differing only in the way the epithelial layer is handled.

Photorefractive keratectomy (PRK) : Using anaesthetic drops ,the corneal epithelium is removed  and excimer laser ablation is performed as required.  No flap is created and a bandage contact lens is used to reduce postoperative pain and promote healing of epithelium which takes a few days.. Recovery time is longer with PRK than with LASIK, though the final outcome (after 3 months) is about the same (very good). The advantage of this procedure is that it can be done on thinner corneas where LASIK is risky.

Laser Assisted Sub-Epithelium Keratomileusis (LASEK) is a procedure similar to PRK except that the corneal epithelium is not removed but rolled over and used as a natural bandage contact lens. 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.

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). But it still is a useful option for lower degrees of myopia , say upto 2-4 where cost of procedure  or availability of Laser machine is a concern.

Limbal relaxing incisions (LRI) are incisions near the outer edge of the iris, used to correct minor astigmatism (typically less than 3 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 improve presbyopia or reading vision after age 40.
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.

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.

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