The cornea is a thin, transparent layer of epithelial tissue that constitutes the surface of the eye, and its function is to refract (or bend) light that enters the eye, causing it to focus on the retina. The term astigmatism refers to a diagnosable change in the shape of the corneal surface.
What causes astigmatism?
In most, the corneal surface is shaped like a symmetrical dome with equal curvature at all points. A child with astigmatism has a corneal surface with varying degrees of steepness. A common analogy compares the astigmatic cornea to a football: While the normal cornea is similar in shape to half of a soccer ball, astigmatism causes it to be shaped like half of a football, coming to a point as it extends outward. Severe cases may be characterized by one or more asymmetric regions of steepness.
While the biochemical basis of astigmatism is not known, it’s the oblong shape of the cornea that leads to many of the associated visual problems. When light passes through the astigmatic cornea, it is not refracted evenly, so some light rays do not fall on the retina at the back of the eye. Several specific vision issues can arise from this condition.
What are the symptoms of astigmatism?
The universal symptom of astigmatism is blurry vision at some or all distances, and one or both eyes may be affected. Undiagnosed children often display multiple telling signs, including irritated eyes, headaches, squinting, and lack of involvement in activities.
There are three types of astigmatism, each associated with a unique visual change: myopic astigmatism, which causes distant objects to appear blurry; hyperopic astigmatism, which causes near objects to appear blurry; and mixed astigmatism, which causes nearsightedness and farsightedness.
How is astigmatism diagnosed?
Astigmatism is diagnosed by a pediatric ophthalmologist or optometrist. Determination of the presence of astigmatism is achieved following a history of vision disturbance. The diagnostic process involves a simple vision test using a standard eye chart, refraction in the refractometer, and measurement of the topography and steepness of the cornea using a procedure called keratoscopy.
How is astigmatism treated?
Once a child is diagnosed with astigmatism, an ophthalmologist decides on the most appropriate method of correcting the problem. Some children respond well to glasses and others to contact lenses. In certain cases, eye surgery is performed by removing corneal tissue from the steep parts of the cornea, effectively “flattening” the astigmatism.