Introduction  

Astigmatism is a common condition where light fails to focus uniformly on the retina. This uneven focus causes blurred or distorted vision at all distances. It occurs as a result of the curvature in the lens or when the cornea is not shaped as it should be. Astigmatism may occur with two other similar refractive error conditions; myopia and hyperopia.

An irregularly shaped cornea or lens will prevent light from focusing correctly on the retina. The vision then becomes blurred or distorted at any distance. A normal eyeball is supposed to take the shape of a round ball, not a football. A diopter (a unit of measurement of the refractive power of a lens) measures astigmatism. A measurement of 1.5 or more means the individual needs glasses or lenses for clear vision. The average diopters measurement in most people ranges from 0.5 to 0.75.

Sub-Types

  • Regular

The cornea is curved more in one direction than the other. 

  • Irregular

The curvature of the cornea is not even.

Causes and Risk Factors

The exact cause of astigmatism largely remains unknown. However, astigmatism is hereditary and is present from birth. People with a family history of astigmatism are more likely to get it. Astigmatism can increase or decrease with time. 

It is also associated with an eye disease, injury to the eye, or surgery.

Astigmatism affects both adults and children. Many people usually have a degree of astigmatism. Adults risk developing cataracts if the curvature of the lens inside the eye changes. The change can lead to the increase or decrease of astigmatism.

Keratoconus can also cause astigmatism. Keratoconus is a disease where the cornea progressively thins and forms the shape of a cone. The result is a large amount of astigmatism which can only be corrected by contact lenses or corneal transplants.

Signs & Symptoms

  • Strain in the eye
  • Headaches
  • A distorted or blurry vision
  • Discomfort in the eye
  • Squinting

 

Diagnosis

To diagnose astigmatism, the eye care professional will conduct a thorough eye examination. The patient is requested to read letters on an eye chart to test visual acuity. The aim is to determine how light is focused in the eyes and the power of the lenses to be prescribed.

The professional may use a phoropter also known as refractor to determine how to shape the eye lens to correct vision. He can also use an autorefractor or retinoscope to determine the corrective lenses needed. A keratometer will establish the exact curvature of that region of the cornea’s surface.

Treatment 

To diagnose astigmatism, the eye care professional will conduct a thorough eye examination. The patient is requested to read letters on an eye chart to test visual acuity. The aim is to determine how light is focused in the eyes and the power of the lenses to be prescribed.

The professional may use a phoropter also known as refractor to determine how to shape the eye lens to correct vision. He can also use an autorefractor or retinoscope to determine the corrective lenses needed. A keratometer will establish the exact curvature of that region of the cornea’s surface.

Medical Treatment

Slight astigmatism does not require treatment. Astigmatism is essentially treated using eyeglasses or contact lenses. These two compensate for uneven curves in the cornea or lens. Rigid contact lenses are used to correct severe astigmatism. The soft toric contact lenses can also correct astigmatism. The eye doctor will determine which is more suitable. 

Another way to treat astigmatism is by use of orthokeratology; a painless, non-invasive procedure that improves vision temporarily. A patient will wear some specially designed rigid contact lenses over a limited period.  For effective treatment, patients must continuously wear these lenses. 
If they stop wearing them, vision will return to its original condition.

Surgical Treatment

Laser surgery can be used to treat astigmatism since it alters the shape of the cornea. The procedure involves removing a small amount of tissue from the astigmatic eye to reshape the cornea. The change restores the focusing power of the eye to focus evenly on the retina.

Prognosis/Long-term outlook

Astigmatism gradually reduces throughout early childhood. Children may not even be aware they have astigmatism. It’s essential that children continuously undergo eye checks to detect the condition early.