Refractive surgery
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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. The most common methods today use lasers to reshape the cornea. With the help of laser or other method it became possible to be no longer dependent on corrective lenses. Successful refractive eye surgery can help to reduce such commom vision disorders 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[link].
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 in 2005. It is performed for a wide range of nearsightedness. The surgeon uses an instrument called a microkeratome to cut a flap of corneal tissue, 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 don't use a microkeratome but cut the flap with a laser (intralase).
- Laser Assisted Sub-Epithelium Keratomileusis (LASEK) is a procedure that permanently changes the shape of the cornea using an excimer laser to ablate a small amount of tissue from the front of the eye, just under the eye's skin or epithelium which is kept and replaced 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. It is a type of refractive surgery which reshapes the cornea by destroying microscopic amounts of tissue from the outer surface with a cool, computer-controlled ultraviolet beam of light (an excimer laser).
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made with a diamond knife) to alter the shape of the cornea and reduce myopia; this technique has now been largely superseded by other methods.
- Arcuate keratotomy (AK) is similar to Radial keratotomy, but the incisions on the cornea are done parallel to the edge of the cornea.
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.
- 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.
- Lens implants can also be used inside the eye to change refractive error. Currently all refractive implants are under investigation by the Food and Drug Administration.
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 [link].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 is not for everybody. People who are slow healers or who have ongoing 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 [link], that may lead to the need for a corneal transplant. Furthermore, some people's eye shape may not permit effective refractive surgery without removing dangerous amounts of corneal tissue. Those considering laser eye surgery are often advised to have a full eye examination with an experienced surgeon.
Other risks even for healthy people may be[link]:
- Infection and delayed healing: There is a less than 0.1 percent chance of the cornea becoming infected after PRK, and a somewhat smaller chance after LASIK. This is uncomfortable, but has no long-term effects after a period of four years.
- Undercorrection/Overcorrection: Predicting perfectly how your eye will respond to laser surgery is not yet possible. Therefore, you may still need corrective lenses after the procedure to obtain good vision. In some cases, a second procedure can be done to improve the result.
- Decrease in Best-Corrected Vision: After refractive surgery, a few patients find that their best obtainable vision with corrective lenses is worse than it was before the surgery. This may happen as a result of irregular tissue removal or the development of corneal haze.
- Excessive Corneal Haze: Corneal haze occurs as part of the normal healing process after PRK. In all but a few cases, it has no effect on the final vision and can only be seen by an eye doctor with a microscope. However, there are some cases of excessive haze that interferes with vision. As with undercorrections, this can often be dealt with by means of an additional laser treatment. The risk of significant haze is much less with LASIK than with PRK.
- Regression: In some patients the effect of refractive surgery is gradually lost over several months. This is like an undercorrection, and a re-treatment is often feasible. But, usually results are permanent.
- Halo Effect: The halo effect is an optical effect that is noticed in dim light. When the pupil enlarges to adapt to the dimmer light, a second faded image is produced by the untreated peripheral cornea. For some patients who have undergone PRK or LASIK, this can interfere with night driving.
- Flap Damage or Loss (LASIK only): Instead of creating a hinged flap of tissue on the central cornea, the entire flap could come loose. If this were to occur it could be replaced after the laser treatment. However, there is a risk that the flap could be damaged or lost.
- Distorted Flap (LASIK only): Irregular healing of the corneal flap could create a distorted corneal shape, which would decrease the best-corrected vision.
- Dry eye: Feeling of dryness, soreness, and discomfort in the eye.
- Altitude effects: Some refractive surgery patients have reported significant changes in vision with changes of altitude (perhaps because oxygen concentration can affect corneal swelling). A patient who achieves good vision at sea level may have poorer results in the mountains.
- Incomplete Procedure: Equipment malfunction may require the procedure to be stopped before completion. This is a more important factor in LASIK, due to its higher degree of complexity, than in PRK.
References
External links
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