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Astigmatism: A common refractive error of the eye

What is astigmatism?

Astigmatism is a common visual disorder marked by blurring of vision due to corneal (the clear part covering the eye) asymmetry or an abnormal curvature of the lens. It can occur both in children and adults.

Astigmatism: A common refractive error of the eye

Causes

  • Astigmatism results when the cornea or lens are not even and smooth, the light rays does not get refracted properly (refractive error) and focused on the light-sensitive layer of the eye (retina).
  • It is often present from birth
  • The other causes of astigmatism include:
    • Corneal injury or infection that scars the cornea
    • Keratoconus and keratoglobus: Eye conditions that make the cornea to bulge, get thinner and change its shape
    • Changes in cornea due to an eye surgery
    • Other eye conditions which affect the eyelids and distort the cornea or lens

Symptoms

The commonly reported symptoms include:

  • Both the near and far away objects appear blurred
  • Squinting and discomfort of eyes
  • Inability to read small print
  • Headache
  • Eyestrain

Power in the eye - What does it mean?

Diagnosis

Your ophthalmologist (eye doctor) will perform a complete eye examination which can include:

  • Visual acuity test: You will be asked to read letters on a chart placed at a standard distance. Visual acuity is represented as a fraction (example, 20/40). The top most number is the standardised testing distance (20 feet), and the bottom number is of the smallest readable size letters. An individual with a visual acuity of 20/40 will have to get within 20 feet to decipher a letter that can be seen clearly at 40 feet.
  • Refraction: An instrument called phoropter is employed, where a series of lenses are placed in front of your eyes to measure the way they focus the light on your retina. It is carried out using a retinoscope or an automated instrument that assesses the estimated focusing power of the eye. Based on the results, the power is arrived at, to determine the exact lenses that offer the clearest vision.
  • Keratometry: A keratometer is an instrument used for measuring the cornea’s curvature. A circle of light is focussed on the cornea and its reflection is measured, this makes it possible to determine the precise curvature of the corneal surface. It is critical in determining the appropriately fitting contact lenses. A contour map of the cornea is generated that offers information on the cornea’s shape.

Treatment

The treatment options for astigmatism include:

  • Corrective lenses: Eyeglasses are the preferred choice for people with this condition. The glasses are tailor-made to compensate for the individual’s astigmatism. Contact lenses offer a clearer vision for some people than glasses. They also provide a wider field of vision. Usually, specialised toric soft contact lenses are prescribed than the standard soft ones.
  • Orthokeratology: It includes the use of an array of rigid contact lenses to reshape the cornea. The contact lenses are worn for a short period, like overnight, and then taken off. Individuals with moderate astigmatism can temporarily achieve clear vision without lenses for most of their routine activities. If one stops wearing the retainer lenses, the vision can go back to its original state.
  • Keratotomy: The cornea can be reshaped by removal of the abnormal corneal tissue either by
    • Laser in situ keratomileusis (LASIK): The cornea’s inner tissue layer is removed.
    • Photorefractive keratectomy (PRK): Here tissues from the cornea’s superficial and inner layers are removed.

Prevention

It can be difficult to prevent astigmatism altogether as the exact causes for the condition are not known.

Complications

Uncorrected astigmatism in children in one eye can cause amblyopia (lazy eye).

Next Steps

Wear your prescribed glasses or contacts for astigmatism. Contact your doctor if you experience any vision problems.

Consult a top Ophthalmologist

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References

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  • What Is Astigmatism? American Academy of Ophthalmology. https://www.aao.org/eye-health/diseases/what-is-astigmatism. Accessed 23 Nov. 16.
  • Facts About Astigmatism. NIH National Eye Institute. https://nei.nih.gov/health/errors/astigmatism. Accessed 23 Nov. 16.
  • U.S. National Library of Medicine MedlinePlus. https://medlineplus.gov/ency/article/001015.htm. Accessed 23 Nov. 16.

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