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What is astigmatism?

  1. Causes
  2. Types
  3. Correction options
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Astigmatism is a type of refractive error caused by the irregularities in the shape of a person’s cornea. The condition is not an eye disease or eye health issue. In this condition, the eye fails to focus the light equally on the retina leading to blurred or distorted vision. It can be present at the time of birth, or can develop gradually in life.

Put simply, Astigmatism is a problem with how the eye focuses light.

Astigmatism is a common eye condition which usually occurs with myopia (nearsightedness) or hyperopia (farsightedness) and can be easily diagnosed with a simple eye exam.

Symptoms of astigmatism include blurred vision or some degree of vision distortion at all distances. Astigmatism can also cause dizziness, eye strain, headaches, squinting and eye irritation.

What causes astigmatism?

Astigmatism is usually caused by an irregularly shaped cornea. Instead of the cornea having a symmetrically rounded ball shape, it is shaped more like an egg, with one side (meridians) being significantly more curved than the side perpendicular to it.

(To understand what meridians are, think of the front of the eye like the face of a clock. A line connecting the 12 and 6 is one meridian; a line connecting the 3 and 9 is another.)

The steepest and flattest meridians of an eye with astigmatism are called the principal meridians.

In some cases, the problem is caused by the distortion of shape of the lens inside the eye. This is called lenticular astigmatism, to differentiate it from the more common corneal astigmatism.

3 types of astigmatism

There are three primary types of astigmatism:

  • Myopic astigmatism.

     One or both principal meridians of the eye are nearsighted. (If both meridians are nearsighted, they are myopic in differing degree.)

  • Hyperopic astigmatism.

     One or both principal meridians are farsighted. (If both are farsighted, they are hyperopic in differing degree.)

  • Mixed astigmatism.

     One prinicipal meridian is nearsighted, and the other is farsighted.

Astigmatism is also classified as regular or irregular. In regular astigmatism, the principal meridians are 90 degrees apart (perpendicular to each other). In irregular astigmatism, the principal meridians are not perpendicular.

For most, the condition is regular corneal astigmatism, which gives the front surface of the eye an oval shape.

Irregular astigmatism can result from an eye injury that has caused scarring on the cornea, from certain types of eye surgery or from keratoconus, a disease that causes a gradual thinning of the cornea.

Astigmatism in children

It is common for babies to be born with astigmatism, but it usually clears up in the first year or so of the child's life. The percentage of children with astigmatism decreases significantly as they reach 5 to 9 years of age.

While most children outgrow eye astigmatism, it is more likely to occur in kids who also struggle with either myopia or hyperopia. Like with adults, mild to severe astigmatism in children can be treated with glasses (or contact lenses if they’re old enough).

Babies do not need to wear glasses to treat their astigmatism as they’re likely to outgrow it before it becomes an issue.

It’s important to schedule an eye exam for your child to avoid vision problems in school from uncorrected astigmatism.

SEE RELATED: Vision problems of preschool children

Astigmatism tests

Astigmatism is detected during a routine eye exam with the same instruments and techniques used for the detection of nearsightedness and farsightedness.

Your eye doctor can estimate the amount of the condition you have by shining a light into your eye while manually introducing a series of lenses between the light and your eye. This test is called retinoscopy.

How to correct astigmatism

Options to correct astigmatism can usually be corrected with eyeglasses, contact lenses or refractive surgery.

Refractive surgery is one of the less common astigmatism treatment options, however, since it is a laser procedure that changes the shape of your eyes, it comes with risks associated with most laser surgeries.

Astigmatism should be treated as soon as possible. Once diagnosed, regular visits to an eye doctor are required as astigmatism can fluctuate over time, making it necessary for prescriptions to be modified.

WORRIED YOUR CHILD MAY HAVE ASTIGMATISM? Book an appointment with a children’s eye doctor near you.

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