Astigmatism

Astigmatism

Definition

Astigmatism is a problem of visual distortion caused by a misshapen cornea. The cornea acts as a focusing lens for the eye. If the cornea does not have the proper shape, the eye is unable to properly focus an image. Most people have a certain degree of astigmatism. Corrective measures are necessary only in cases where the distortion is severe.

Description

Light rays entering a normal eye come to a point of focus on the retina through a transparent, dome-shaped layer called the cornea. In astigmatism there is unequal curvature of the cornea, and the light rays come to focus at more than one point on the retina. This causes the person to see a blurred or doubled image. Astigmatism is usually present at birth and may increase during childhood as the eye tissue develops. Usually the degree of astigmatism remains fairly constant throughout adulthood.

Causes & symptoms

It is unknown why some people develop a misshapen cornea. It is possible that astigmatism is an inherited trait. Factors such as stress , continual reading in dim lighting, or excessive close-up work may also contribute to the development of astigmatism. It is sometimes caused by pressure from chalazion, a condition that causes the eyelid to swell; from scars on the cornea; or from keratoconus, a condition that involves swelling of the cornea. The main symptom of astigmatism is blurred or distorted vision. There may also be a history of headaches, eye strain, fatigue , and double vision.

Diagnosis

The standard eye examination with a refraction test, given by an optometrist or opthalmologist, is

used to determine the presence of astigmatism. An instrument called a keratometer is used to measure the cornea and calculate the shape of the required corrective lens.

Treatment

The Bates method or other type of visual training may be helpful in improving vision and reducing symptoms. The homeopathic remedies Ruta graveolens (from common rue) and Apis mellifica (from the honey bee) can be used to relieve eyestrain, one of the main symptoms and possible contributors to astigmatism.

Acupuncture treatment or Traditional Chinese Medicine may help, as the liver system is connected to eye functions. Certain treatments can strengthen and correct the skewing of the Liver qi. (Qi is the flow of energy in the body. It is sometimes associated with certain organs.)

Allopathic treatment

Astigmatism can be most simply treated with either eyeglasses or contact lenses. The lenses are made so as to counteract the shape of the sections of cornea that are causing difficulty. Contact lenses that are used to correct astigmatism are called toric lenses. Hard contact lenses may be better for correcting astigmatism than soft contact lenses. In the case of keratoconus, a corneal transplant is performed if the astigmatism cannot be corrected with hard contact lenses.

Refractive surgery can be performed to correct the curvature of the cornea. In radial keratotomy (RK) for astigmatism, cuts are made into the cornea with a diamond blade instrument. In photorefractive keratectomy (PRK), a laser is used to improve the shape of the cornea by removing micro-thin slices. Laser assisted in situ keratomileusis (LASIK) is the most recently developed type of refractive surgery. A flap of the cornea is cut with a laser and then the corneal tissue underneath is shaved to improve the shape.

Doctors continue to improve LASIK techniques. In 2002, a cross-cylinder method was developed in refractive surgery to help treat mixed astigmatism, one of the most difficult types to treat. Refractive surgery requires a high level of expertise. Anyone considering it should make sure that the surgeon has a lot of experience in the procedure. There should also be an in-depth discussion of the possible side effects and risks of the procedure. For instance, patients with flatter corneas seem to come out of surgery with more light distortion than those with curved corneas. Pupil size also may affect surgery outcome.

Expected results

Effects of astigmatism can generally be greatly improved with eyeglasses or contact lenses. Refractive surgery may diminish the need for lenses or make them unecessary altogether. The major risks of surgery include chronic visual problems, injury to the eye tissue, infection, and over- or under-correction, which would still leave some astigmatism. Complications may require the use of medication or further surgery.

Resources

BOOKS

Lininger, Skye, ed. The Natural Pharmacy. Rocklin, Calif.: Prima Health, 1998.

Newell, Frank W. Ophthalmology, Principles and Concepts. 8th ed. St. Louis: Mosby, 1996.

PERIODICALS

"Clues to LASIK Vision Problems (Risk of 'Starbursts')." Prevention (June 2002): 161.

Meszaros, Liz."Cross-Cylinder Technique Offers Many Benefits, Little Trauma: Method to Correct Mixed Astigmatism Minimizes Tissue Removal, not Ideal for High-Correction Cases." Ophthalmology Times (May 15, 2002): 41.

OTHER

"Refractive Surgery." The Merck Manual Online. (December 2000).<http://www.merck.com/pubs/mmanual/section8/chapter102/102c.htm/>.

Patience Paradox

Teresa G. Odle