What Is Astigmatism?

Astigmatism is a vision problem that causes blurriness, visual distortion, and difficulty seeing at night, among other symptoms. Researchers don't exactly know what causes astigmatism, but they do know that the condition occurs when the cornea (or, the outermost layer of your eye) changes in shape. You may also be at an increased risk of developing astigmatism if you have a family history of the condition, experience an eye injury, or undergo eye surgery.

It's estimated that 40% of the population will experience this condition at some point in their lifetime. Fortunately, there are several treatment options that focus on correcting astigmatism. These include getting glasses, using special contact lenses, or having surgery to fix the shape of the cornea.

Types of Astigmatism

The type of astigmatism you have can help your eye care provider figure out the treatment options that are right for you. There are several types of astigmatism, including:

• Corneal: The most common type which occurs when there is a change in the curvature or shape of the cornea
• Lenticular: Happens when there is a change in the lens of the eye
• Myopic: A type of astigmatism that occurs in people who have nearsighted eyes
• Hyperopic: A type of astigmatism that occurs in people who have farsighted eyes
• Mixed: Affects people who are farsighted in one eye and nearsighted in the other eye

Symptoms

The most common symptom of astigmatism is changes in your ability to see properly. That said, a variety of other vision-related symptoms may also occur, including:

• Blurry vision: Astigmatism affects your ability to see things close by and far away. It's common to experience blurriness or other vision distortions.
• Squinting: This common reaction of partially bringing your eyelids together occurs when your eyes aren't able to see clearly.
• Eye strain: When you can’t see as well, squinting can cause eye strain or fatigue, resulting in your eyes feeling heavy, watery, or burning. As a result of the eye strain, it can also be common to experience headaches.
• Trouble seeing in the dark: Astigmatism can sometimes make it difficult for your eyes to adjust to changes in lighting. That said, some people experience trouble seeing at night or in other low-light conditions.
  

Causes

In eyes without astigmatism, light enters the eye and hits the retina—which is a sensitive layer located at the back of the eye that is responsible for sending information to the optic nerve in your brain. As light enters your eye, your retina triggers nerve impulses to your brain. When your optic nerve becomes triggered, your brain is able to process a visual image for your eyes to see.

However, when you have astigmatism, your retina isn't able to function properly, which can affect your vision. The reason this happens is because astigmatism causes your eyes to change shape. As a result, you aren't able to properly focus on the objects in front of you, which can make your vision seem blurry or distorted.

Why exactly astigmatism happens is currently unknown. Some researchers theorize that normal changes in vision as you age or having an underlying eye condition can all increase your risk of developing astigmatism.

Risk Factors

Anyone can develop astigmatism, but some factors may increase your likelihood of experiencing symptoms of the condition. These risk factors include:

• Having a family history of astigmatism
• Experiencing an injury to the eye
• Undergoing eye surgery or having complications after the procedure

Diagnosis

If you notice changes to your vision, it's good practice to see your eye care provider (such as an optometrist or ophthalmologist) for testing. During your eye exam, your provider can learn more about your symptoms, check your vision, and rule out other conditions that may be causing blurriness or eye strain.

Your provider can perform a number of diagnostic tests to learn more about your condition and test for other eye conditions (such as nearsightedness or farsightedness). These tests include:

• Visual acuity: Tests how well you see objects close by and far away by reading letters of different sizes on a chart
• Refraction: Assesses how much refractive error (lack of focus in the eyes) you have
• Retinoscopy: Uses a handheld device called a retinoscope to test the level of refractive error in your eye
• Keratometry: Involves using a device known as a keratometer to measure the curvature and shape of the cornea
• Pachymetry: Measures the thickness of the cornea while using a device called a pachymeter to determine if you need eye surgery

Treatment

Depending on the severity of your condition, there are a variety of treatment options that your eye care provider can consider. The goal of astigmatism treatment is to correct the underlying cause of your symptoms or reduce the intensity of your symptoms.

Mild cases of astigmatism may not always require treatment, but will often need regular check-ups to assess the progress of your condition. More severe astigmatism cases may involve treatment options such as glasses, corrective lenses, or surgery.

Refractive Surgery

If your eye care provider thinks surgery is right for you, they may recommend procedures that help reshape your cornea to correct the astigmatism. Typically, these surgeries are successful and lead to permanent results. Your provider may consider one of the following procedures:

• Astigmatic keratectomy: Involves making tiny incisions (cuts) in the cornea to help change the way light enters your eye
• Laser in-situ keratomileusis (LASIK): LASIK surgery relies on using laser beams to remove tissue from the inner cornea, which helps reshapes the eye
• Photorefractive keratectomy (PRK): Like LASIK, PRK surgery works to change the shape of the eye by scraping layers of the inner and outer cornea away with a laser

Orthokeratology

Orthokeratology, or wearing night lenses, is a non-surgical approach that involves wearing specialized, rigid contact lenses at night to help readjust the shape of the cornea. During this course of treatment, you may go through one or more sets of overnight lenses as the structure of your eye slowly changes. It's important to note that these changes aren't permanent, but ongoing treatment can help you see clearly.

Glasses and Contact Lenses

Some people may need eyeglasses that are made with special lenses called cylindrical lenses to help reduce astigmatism symptoms. The cylindrical lenses are able to help improve visual acuity (sharpness) and reduce eye strain associated with astigmatism.

If you prefer contact lenses to glasses, talk to your eye care provider to see if contact lenses for astigmatism are right for you. Keep in mind: those who wear contact lenses should be extra careful about cleaning and caring for their lenses to prevent infection or other eye problems.

It's also worth noting that soft contact lenses that most lens wearers use are not helpful for astigmatism. That's because regular contact lenses are made for corneas with a round shape, whereas people with astigmatism have corneas that are more curved and resemble the shape of a football.

Those with astigmatism can instead benefit from wearing "toric" lenses, which are contacts that are shaped in a specific way to help reduce the effects of astigmatism and are more effective in improving symptoms. Toric lenses also include lines or markings on the contacts that are specifically made to correct your astigmatism. The purpose of these lines is to help your provider check if the lenses are fitting properly and sitting on your eyes correctly.

How to Prevent Astigmatism 

Unfortunately, because the exact cause of astigmatism is unknown, there is no surefire way to prevent the condition. Additionally, contrary to popular belief, lifestyle habits like excessive squinting or watching too much TV don’t lead to this condition. However, it's important to note that young children of preschool age who are exposed to too much screen time may be at a higher risk of developing astigmatism later in life.

For some people, astigmatism can actually get better on its own, and mild cases may not require treatment. That said, astigmatism—especially if associated with changes in cornea shape—should always be monitored by your eye care provider.

However, since the condition can become worse, there are ways to prevent your condition from worsening. This may include following your treatment plan as prescribed and getting regular eye exams.

Related Conditions

Living with astigmatism increases your risk of developing other vision problems. These conditions may include:

• Vision loss: Myopia (inability to see clearly far away) and hyperopia (inability to see things nearby) often occur alongside astigmatism.
• Cataracts: Cataracts are cloudy spots on your lens that can develop as you age. Studies have found that 35% to 40% of people with cataracts also have astigmatism.
• Amblyopia: Also known as lazy eye, amblyopia is a visual defect in one eye that occurs due to overuse or reliance on the other eye. Astigmatism in one eye—especially in infancy or childhood—can lead to this condition.
• Strabismus: Commonly called “crossed eyes,” strabismus is when the eyes don’t line up properly. Some research suggests that untreated astigmatism can sometimes increase your risk of developing this condition.

Living With Astigmatism

There is no surefire way to prevent astigmatism. However, treatment (e.g., surgery, lenses, or glasses) can improve your symptoms and correct the underlying cause of your vision changes. If the condition is left untreated, it may significantly affect your ability to perform daily tasks.

While astigmatism can affect your vision, most people who receive treatment continue to live healthy and normal lives. However, it's critical to seek out support from your eye care provider if you experience symptoms so they can properly diagnose you and offer appropriate treatment.