Astigmatism is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina, the light sensitive surface at the back of the eye. As a result, vision becomes blurred at any distance.
Astigmatism is a very common vision condition. Most people have some degree of astigmatism. Slight amounts of astigmatism usually don’t affect vision and don’t require treatment. However, larger amounts cause distorted or blurred vision, eye discomfort and headaches.
Astigmatism frequently occurs with other vision conditions like nearsightedness (myopia) and farsightedness (hyperopia). Together these vision conditions are referred to as refractive errors because they affect how the eyes bend or “refract” light.
The specific cause of astigmatism is unknown. It can be hereditary and is usually present from birth. It can change as a child grows and may decrease or worsen over time.
A comprehensive optometric examination will include testing for astigmatism. Depending on the amount present, your optometrist can provide eyeglasses or contact lenses that correct the astigmatism by altering the way light enters your eyes.
Laser surgery known as LASIK and PRK, is also a possible treatment option for some types of astigmatism. It changes the shape of the cornea by removing a small amount of eye tissue. This is done using a highly focused laser beam on the surface of the eye.
What Causes Astigmatism?
Astigmatism occurs due to the irregular shape of the cornea or the lens inside the eye. The cornea and lens are primarily responsible for properly focusing light entering your eyes allowing you to see things clearly.
The curvature of the cornea and lens causes light entering the eye to be bent in order to focus it precisely on the retina at the back of the eye. In astigmatism, the surface of the cornea or lens has a somewhat different curvature in one direction than another. In the case of the cornea, instead of having a round shape like a basketball, the surface of the cornea is more like a football. As a result, the eye is unable to focus light rays to a single point causing vision to be out of focus at any distance.
Sometimes astigmatism may develop following an eye injury or eye surgery. There is also a relatively rare condition called keratoconus where the cornea becomes progressively thinner and cone shaped. This results in a large amount of astigmatism resulting in poor vision that cannot be clearly corrected with spectacles. Keratoconus usually requires contact lenses for clear vision, and it may eventually progress to a point where a corneal transplant is necessary.