Definition
Astigmatism is when the curvature of the cornea, or a lens, varies in different directions. An astigmatic surface is often referred to as being "rugby ball" in shape compared with a "football" shaped spherical surface.
Incidence/Age
A small amount of astigmatism is so common in all age groups that it can be considered the norm. High levels of astigmatism are fortunately much rarer.
Causes
Astigmatism has no specific cause, but is commoner in premature babies. There can be genetic influences, with moderate to marked astigmatism occasionally being transmitted from parents to their offspring. More rarely astigmatism can be induced by pressure on the eyeball, eg, secondary to eyelid cysts. The shape of the eye can be warped after ocular surgery, eg, corneal graft, especially when stitching is necessary.
Symptoms and Signs
Astigmatism causes a blurred picture on the retina at the back of the eye, which can result in poor distance and near vision. High amounts of induced astigmatism, eg, after eye trauma or eye surgery can make the vision distorted, sometimes giving objects a "stretched out" or tilted appearance.
Complications of Disorder
Significant childhood astigmatism can cause permanent lazy vision (amblyopia) in one or both eyes if undetected at an early age, with an increased incidence of squint (misalignment of the eyes).
Tests
An eye examination, using optical lenses, can detect the degree of astigmatism and any affect on the level of vision in each eye. Other techniques, eg, keratometry, corneal topography, can provide more detail on the shape and curvature of the front of the eye (cornea).
Treatment:
Astigmatism can usually be corrected with suitable spectacle lenses. Contact lenses can also be effective, but may require specialist fitting. Rigid contact lenses, eg, gas permeable lenses are usually preferred, often providing better vision than flexible soft contact lenses.
Refractive surgery, which involves making relieving cuts into the cornea at the front of the eye, or EXCIMER laser treatment may be beneficial in selected cases at reducing levels of astigmatism.
Outcome/Prognosis
Good vision is usually achievable with corrective lenses, but blurred vision can result in children who do not have moderate to marked astigmatism detected and treated at an early age.
Source:privatehealth.co.uk
Last Editorial Review:20/1/2010
