What Is the Main Cause of Astigmatism?

Reviewed on 2/2/2021

What Is Astigmatism?

Astigmatism causes blurry vision resulting from an irregularity of the eye's lens or cornea. These irregularities may stem from genes, injury or certain eye diseases.
Astigmatism causes blurry vision resulting from an irregularity of the eye’s lens or cornea. These irregularities may stem from genes, injury or certain eye diseases.

Astigmatism is a common vision problem that can cause blurred or distorted vision, making it hard to see clearly. It is a type of refractive error that occurs when the cornea (the clear front layer of the eye) or lens (an inner part of the eye that helps the eye focus) has a different shape than normal so the eye cannot focus properly.

Refractive errors are the most common type of vision problem.

What Are Symptoms of Astigmatism?

Mild astigmatism may not cause any symptoms. When symptoms of astigmatism occur, they may include:

  • Blurred vision
  • Needing to squint to see clearly
  • Headaches
  • Eye strain
  • Difficulty seeing at night
    • Glare
    • Starburst patterns and halos around lights

What Causes Astigmatism?

Astigmatism occurs when the cornea or lens is irregularly-shaped. This abnormal shape causes to light bend differently as it enters the eye, resulting a refractive error and an inability to focus. 

Some causes of astigmatism may include: 

  • Genetics
  • Eye injury
  • Eye surgery
  • Corneal diseases such as keratoconus

How Is Astigmatism Diagnosed?

Astigmatism is diagnosed with a dilated eye exam. To perform the exam, a doctor will give drops to dilate (widen) the pupil. 

A dilated eye exam includes:

  • Dilation 
    • Checks for problems with the inner parts of the eye
    • The eye drops dilate (widen) the pupils so the doctor can see inside the eye
  • Visual acuity test
    • Checks vision clarity
    • Patients read letters up close and far away
  • Visual field test 
    • Checks peripheral (side) vision
    • Tests how well you can see objects in your peripheral vision without moving your eyes
  • Eye muscle function test 
    • Check for problems with the muscles around the eyeballs
    • Patients follow a moving object with their eyes
  • Pupil response test 
    • Checks how light enters the eyes
    • The doctor shines a small flashlight into the eyes to check how the pupils react to the light
  • Tonometry test 
    • Measures pressure in your eyes
    • A quick puff of air is blown onto the eye, or the eye is gently touched with a special tool (this is not painful)

What Is the Treatment for Astigmatism?

Mild astigmatism may not require treatment if the patient has no noticeable symptoms. 

Astigmatism can be treated with: 

  • Corrective eyeglasses 
  • Contact lenses
  • Laser refractive surgery
    • Photorefractive keratectomy (PRK)
    • LASIK
  • Orthokeratology lenses 
    • Rigid gas permeable contact lenses used while sleeping to temporarily reshape the corneas overnight
  • Refractive lens exchange
    • Removes the natural lens in the eye (same procedure as cataract surgery
    • A toric intraocular lens is inserted, which is an implant that corrects astigmatism
    • A better option for older patients who have higher astigmatism corrections and may develop cataracts soon
  • Phakic intraocular lens implant
    • Usually reserved for patients with high nearsightedness (myopia)
    • A posterior chamber phakic lens implant is inserted in front of the natural lens, or an anterior chamber phakic lens is placed in front of the iris


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Reviewed on 2/2/2021