Astigmatism

Astigmatism, cornea, excimer laser, eye surgery, hyperopia, laser-assisted in situ, laser epithelial keratomileusis, laser vision correction, LASIK, keratomileusis, myopia, photorefractive keratotomy (PRK), refractive eye surgery, refractory surgery, vision correction.

LASIK is the acronym for laser in situ keratomileusis, sometimes referred to as laser-assisted in situ keratomileusis. The name refers to the use of a laser to reshape the cornea without invading the neighboring cell layers. In situ is Greek for "in the natural or normal place." Medically, in situ means confined to the site of origin without invasion of neighboring tissues. Kerato is the Greek word for cornea and mileusis means "to shape."

LASIK is a type of refractive eye surgery that may reduce a person's dependency on glasses or contact lenses by permanently changing the shape of the cornea (the delicate clear covering on the front of the eye).

Refractive eye surgery is a surgical procedure that changes the way the eye refracts light. As light rays enter the eye, the cornea and lens bend (refract) the rays to focus them on the back of the eye, the retina. If a patient has a refractive error, the eye is shaped in such a way that light rays are not sharply focused on the retina.

The cornea is the part of the eye that helps focus light to create an image on the retina. Usually the shape of the cornea and the eye are not perfect and the image on the retina is out-of-focus (blurred) or distorted. These imperfections in the focusing power of the eye are called refractive errors.

There are three primary types of refractive errors: myopia, hyperopia and astigmatism. Persons with myopia, or nearsightedness, have more difficulty seeing distant objects as clearly as near objects. Persons with hyperopia, or farsightedness, have more difficulty seeing near objects as clearly as distant objects. Astigmatism is a distortion of the image on the retina caused by irregularities in the cornea or lens of the eye. Combinations of myopia and astigmatism or hyperopia and astigmatism are common. LASIK surgery is most commonly used to correct myopia.

LASIK eye surgery was developed in 1990 by doctors Lucio Buratto and Ioannis Pallikaris. It is a refinement of an earlier procedure, photorefractive keratotomy (PRK), which also uses ultraviolet laser light to disrupt tissue in the cornea for removal or reshaping to achieve sharper vision. LASIK has been performed internationally for approximately ten years. It was first performed in clinical trials in the United States in 1995. The United States Food and Drug Administration provides a complete listing of the approval status of excimer lasers in the US on their LASIK website.

Both near and farsighted people may obtain benefits from LASIK eye surgery. The goal of the surgery with nearsighted people is to flatten the cornea and the reverse is true of farsighted people. LASIK surgery may also be beneficial for people who suffer from astigmatism. In this procedure, the laser is used to smooth the irregularly shaped cornea into a more normal shape.

The Academy of Ophthalmology (AAO) reports that of approximately 500,000 Americans who had LASIK surgery in 1999, 70% had 20/20 vision after surgery.

For low to moderate myopia, results from studies in the literature have shown that LASIK may be effective and predictable in terms of obtaining very good to excellent uncorrected visual acuity (sharpness) and that it is safe in terms of minimal loss of visual acuity. For moderate to high myopia, the results are more variable, given the wide range of preoperative myopia. The results are similar for treated eyes with mild to moderate degrees of astigmatism. Side effects such as dry eyes, nighttime starbursts, and reduced contrast sensitivity may occur relatively frequently.

For low to moderate hyperopia (farsightedness), results from published studies have shown that LASIK may be effective and predictable in achieving very good to excellent uncorrected visual acuity (sharpness) and may be safe in terms of minimal loss of best-corrected spectacle vision. Although there is little data for hyperopic astigmatism, the results available seem to mirror the data for low to moderate hyperopia. Utilizing hyperopic LASIK for the treatment of consecutive hyperopia and astigmatism may also be effective, although the ability to reduce hyperopic astigmatism after radial keratotomy is limited. Serious adverse complications leading to permanent visual loss are possible.

A 2003 study reported in the medical journal Ophthalmology found that nearly 18% of treated patients and 12% of treated eyes needed retreatment. The authors concluded that higher initial corrections, astigmatism and older age are risk factors for LASIK retreatment.

This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

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Cobo-Soriano R, Calvo MA, Beltran J, et al. J Cataract Refract Surg 2005 Jul;31(7):1357-65.IG.Thin flap laser in situ keratomileusis: analysis of contrast sensitivity, visual, and refractive outcomes.

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Candidacy: The Food and Drug Administration (FDA), in cooperation with the American Academy of Ophthalmology, has developed the following guidelines and recommendations for good candidates for LASIK: A patient should be at least 18 years old (21 for some lasers), since the vision of people younger than 18 usually continues to change. An exception is the small child with one very nearsighted and one normal eye. The use of LASIK to correct the very nearsighted eye may prevent amblyopia (lazy eye). Pregnant or nursing patients are not good candidates because these conditions might change the measured refraction of the eye. A patient should not be taking certain prescription drugs, such as Accutane or oral prednisone. The eyes must be healthy and the prescription stable. If a patient is myopic, a patient should postpone LASIK until the refraction has stabilized, because myopia (inability to see distant objects) may continue to increase in some patients until their mid to late 20s. A patient should be in good general health. LASIK may not be recommended for patients with diabetes, rheumatoid arthritis, lupus, glaucoma, herpes infections of the eye, or cataracts. A patient should discuss this with the surgeon. For patients with presbyopia (inability of the eye to focus sharply on nearby objects), LASIK cannot correct so that one eye can see at both distance and near. However, LASIK can be used to correct one eye for distance and the other for near. If a patient can adjust to this correction, it may eliminate or reduce the need for reading glasses. In some instances, surgery on only one eye is required.

Preoperative procedure: Before the surgery, the surfaces of the patient's corneas are examined with a computer-controlled scanning device to determine their exact shape. Using low-power lasers, it creates a topographic (showing surface features) map of the cornea. This process also detects astigmatism (a distortion of the image on the retina caused by irregularities in the cornea or lens of the eye) and other irregularities in the shape of the cornea. Using this information, the surgeon calculates the amount and locations of corneal tissue to be removed during the operation. The patient typically is prescribed an antibiotic to start taking beforehand to minimize the risk of infection after the procedure.

Operative procedure: A numbing drop will be placed in the eye, the area around the eye will be cleaned and an instrument called a lid speculum will be used to hold the eyelids open. A ring will be placed on the eye and very high pressures will be applied to create suction to the cornea. The vision will dim while the suction ring is on and a patient may feel the pressure and experience some discomfort during this part of the procedure. The microkeratome, a cutting instrument, is attached to the suction ring. The doctor will use the blade of the microkeratome to cut a flap in the cornea.

The microkeratome and the suction ring are then removed. A patient will be able to see but may experience fluctuating degrees of blurred vision during the rest of the procedure. The doctor will then lift the flap and fold it back on its hinge and dry the exposed tissue.

The laser will be positioned over the eye and the patient will be asked to stare at a light. This light is to help a patient keep the eye fixed on one spot once the laser comes on. When the eye is in the correct position, the doctor will start the laser. The pulse of the laser makes a ticking sound. As the laser removes corneal tissue, some people have reported a smell similar to burning hair. A computer controls the amount of laser energy delivered to the eye. Before the start of surgery, the doctor will have programmed the computer to vaporize a particular amount of tissue based on the measurements taken at the initial evaluation. After the pulses of laser energy vaporize the corneal tissue, the flap is put back into position.

A shield should be placed over the eye at the end of the procedure as protection since stitches are not used to hold the flap in place. It is important for a patient to wear this shield to prevent rubbing the eye or putting pressure on the eye while sleeping and to protect the eye from accidentally being hit or poked until the flap has healed.

The operation is performed with the patient awake. However, the patient may be given a mild sedative (such as Valium or diazepam) and anesthetic eye drops. The surgery usually takes less than 30 minutes.

After surgery: Immediately after the procedure, the eye may burn, itch, or feel like there is something in it. A patient may experience some discomfort, or in some cases, mild pain and the doctor may suggest a mild pain reliever. Both the eyes may tear or water. In addition, a patient may experience sensitivity to light, glare, starbursts or haloes around lights, or the whites of the eye may look red or bloodshot. These symptoms should improve considerably within the first few days after surgery. A patient should plan on taking a few days off from work until these symptoms subside. Contact a qualififed healthcare professional immediately if experiencing severe pain, or if vision or other symptoms get worse instead of better.

A patient should see the doctor within the first 24 to 48 hours after surgery and at regular intervals after that for at least the first six months. At the first postoperative visit, the doctor will remove the eye shield, test the vision and examine the eye. The doctor may give the patient one or more types of eye drops to take at home to help prevent infection and/or inflammation. A patient may also be advised to use artificial tears to help lubricate the eye. Wearing a contact lens in the operated eye is not recommended, even if the vision is blurry.

During the first few months after surgery, the vision may fluctuate. It may take up to three to six months for the vision to stabilize after surgery. Glare, haloes, difficulty driving at night, and other visual symptoms may also persist during this stabilization period. If further correction or enhancement is necessary, a patient should wait until the eye measurements are consistent for two consecutive visits at least three months apart before re-operation.

The price practices charge will vary, depending upon the conditions specific to the patient and the country. Although LASIK is not a cosmetic procedure, it is considered an elective surgery. Such surgeries are covered in many European and Asian countries. However, most United States (US), Canadian and Latin American insurance policies will not cover the procedure, nor will Medicare usually cover it. If a patient resides in the US, a patient should check with the insurance company to see if the policy offers partial or full coverage. In many cases, the cost of the procedure can be covered by medical flex plans or medical cafeteria plans that allow pretax dollars to be set aside for medical expenses. A patient should check with the employer to see if the company offers this type of benefit. It is possible that the cost of LASIK may be deducted from the US federal income taxes. A patient should check with accountant to see if a patient can take LASIK as a deductible health expense. Many ophthalmologists in the US also offer financing plans to patients.