What is Astigmatism?  Definition

Astigmatism is one of a group of eye conditions, called refractive errors, that cause a disturbance in the way light rays are focused within the eye. This occurs when the cornea, a thin sheet of clear tissue covering the eye around the pupil, is irregularly curved. Normally, the eye is a near-perfect sphere, but in astigmatism, the front surface of the cornea is curved more in one direction than in the other--more football-shaped than basketball-shaped. In fact, most astigmatic corneas have two axes of irregular curvature, one flatter than the other. This distortion causes an inability of the eye to focus light rays correctly onto the retina and may result in vision resembling the distortion in a funhouse mirror. This blurred vision applies to objects at all distances, though the condition may be accompanied by near- or far-sightedness. Unequal astigmatism may ultimately lead to amblyopia, or "lazy eye," a condition in which one eye suffers loss of acuity due to the patient favoring his or her other, less astigmatic, eye.

Astigmatism can be Mild or Serious

Not all people with astigmatism require medical assistance; the distortion can be fairly mild. Some experts believe all human beings have a degree of astigmatism. However, in many cases the curvature of the eye is more severe, and corrective lenses must be used to refocus light rays in the eye. These corrective aids may take the form of spectacles or contact lenses. Many astigmatic patients use specially curved contact lenses called toric lenses, which include an additional power element called a cylinder. These lenses bend incoming light farther in one direction than in another in order to oppose the refractive effects of eye curvature. Astigmatism may also be corrected by a refractive surgical procedure called laser-assisted in-situ keratomileusis, or lasik for short. Radio keratotomy and astigmatic keratotomy are two older forms of corrective corneal surgery.

Symptoms

Symptoms of astigmatism include blurring or distortion of images at all distances, plus headache, fatigue, eye irritation, and frequent squinting. These symptoms may grow more intense as a person gets older, so it's a good idea to get regular eye check-ups, especially if a person has already been fitted for corrective lenses. The patient's prescription may need to be altered in order to correct for changes in eye curvature.

Diagnosis

Astigmatism is easily diagnosed by a standard ophthalmic exam that includes a refraction test. Special tests are seldom required. Children, or other patients who are unable to respond to questions, can have their refractive errors measured by a test (called retinoscopy) that uses reflected light.

Astigmatism is usually present from birth. Its cause is unknown.