A person has astigmatism when the light that enters the eye is not focused to a clear point on the retina. Instead light is focused into a line not a point. This means that the person with this condition will have blurred vision. It is present in about thirty to forty percent of people wearing glasses.
What Causes Astigmatism?
The condition can be caused by a variety of ocular conditions. The most common are that the cornea (clear portion in front of the eye) is shaped more like a football versus a basketball and that light that is focused by the lens in the eye does so in a manner that is not symmetrical. This leads to the light being focused in a line. There are other much less common causes such as changes in the retina and injuries.
This type is the most common and it is characterized by the astigmatism being symmetrical. The axes of the two meridians are 90 degrees apart.
The irregular type is much less common. It can be caused by corneal scarring and abnormal focusing of the lens. This type cannot be corrected by glasses. In many cases a contact lens will correct the irregular astigmatism.
Astigmatism with Myopia (nearsightedness), Hyperopia (farsightedness)
A person can be nearsighted or farsighted and have astigmatism as well. There are two levels of astigmatism – simple and compound. Compound means that the person has a more severe level of myopia or hyperopia. There is also mixed astigmatism. It means that the person is neither nearsighted nor farsighted. Their refractive error is only astigmatism.
Usually astigmatism is found when you go to the eye doctor and they put you behind a machine that corrects your vision called a phoropter. There are other tests that can be used to diagnose such corneal topography instruments, autorefractor, keratometer, and/or retinoscopy.
Correction of the condition is usually done by wearing glasses or contact lenses. Toric soft contact lenses or gas perm semi-hard contact lenses are used to correct the condition.
Surgical Correction or Procedures
The condition can be surgically corrected. The surgery is designed to change the shape of the cornea from a football to a basketball.
Limbal Relaxing Incision (LRI) or Astigmatic Keratotomy (AK)
An incision is made in the cornea near the limbus (junction of the cornea and sclera or white portion of the eye). The incisions are made through the majority of the thickness of the cornea in alignment with the steep axis of the astigmatism to flatten the steep side of the football.
Laser Correction of Astigmatism
LASIK, LASEK, and/or PRK can be used to correct the condition. The laser changes the shape of the cornea resulting in correction of the condition.
Astigmatism is a very common refractive error and can be associated with myopia or hyperopia. Glasses and contact lenses are usually used to correct the condition. Corneal incisions and laser surgery can be used to treat or correct the visual condition.