What is Astigmatism? Causes, Symptoms, Diagnosis, and Treatment

Astigmatism is a vision problem that results from an irregular curvature of the cornea or the lens. The eye is usually spherical in people with normal vision. The cornea, the clear front part of the eye, has a regular semi-circular curvature while the lens is biconvex or semi-circular on both sides.

In someone who has an astigmatism, the irregular shape of either the cornea or lens causes improper focusing of light on the retina. The lack of a smooth round curvature makes it impossible to focus light on a single point. As a result, you will have difficulty seeing at any distance.

As more changes in the lens take place, the astigmatism worsens, especially in people about to develop cataracts. In most cases, astigmatism co-occurs with other refractive errors such as nearsightedness and farsightedness. Fortunately, improvements in eye-care medicine have made an astigmatism a very fixable problem, either through glasses or surgery.

Dealing with an astigmatism is a lot less scary if you understand how it is caused and treated.

What Does Astigmatism Do?

If you have an astigmatism, the cornea or the lens is not evenly curved, so naturally you have bad vision. Instead of the light rays being focused to a single point on the retina, they are scattered to different areas at the back of the eye. This diffuse refraction and improper focusing of light rays lead to a blurred or distorted vision for near and far objects.

The effect of this scattering in those with an astigmatism is comparable to using a fun mirror in which you can appear too short, too tall or too thin.

Adults easily detect vision changes caused by astigmatism but children with the condition often don’t know that anything is wrong because they think poor vision is the norm. It can lead to poor performance in class or in sports until it is corrected.

According to the American Academy of Ophthalmology, a regular eye exam for both adults and children is essential for the early identification and treatment of astigmatism. 

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Types of Astigmatism

There are many different ways to classify astigmatism. The most common is to determine if it is caused by the cornea or lens. When the shape of your cornea is distorted, you will have corneal astigmatism, while distortion of the lens curvature gives lenticular astigmatism.

Regular or irregular astigmatism is another classification system that depends on how perpendicular things are with the meridians of the eye. Meridians are like lines on the curvature of the cornea. With-rule, against-rule, and oblique astigmatism are subtypes of regular astigmatism.

Signs and Symptoms of Astigmatism

The symptoms of astigmatism vary from one person to another depending on the type of the refractive error. If you have the condition, you might experience:

• Blurry vision of up close and far objects
• Eyestrain and associated headaches
• Squinting when trying to focus
• Poor night vision
• Irritation of the eyes

These symptoms can occur in other eye conditions as well. So, it is essential to visit an ophthalmologist or optometrist for a comprehensive eye exam to diagnose any symptoms.

Causes and Risk Factors of Astigmatism

Although astigmatism is a common eye condition, how it develops is unclear. Doctors and researchers don’t know what causes an abnormal curvature of the lens and cornea.

Some people are born with it, but most people develop astigmatism during childhood or adulthood. Children born with astigmatism often have either one or both parents with the condition meaning the refractive error is hereditary.

Someone with non-astigmatic relatives can develop the disorder following an eye injury or surgery.

While anyone can develop astigmatism, the risk is higher if you have:

• A family history of astigmatism
• Keratoconus, characterized by progressive thinning of the cornea
• Excessive nearsighted or farsightedness
• Undergone cataract surgery or other types of eye surgery

How Will My Doctor Diagnose Astigmatism?

If you have symptoms that point to astigmatism, your doctor will perform a complete eye exam to diagnose the condition. They will use different tests that measure the clarity of your vision, how your eyes focus the light rays, and the contour of your cornea.

Astigmatism tests include:

Visual acuity

Your doctor will ask you to stand at a distance of 20 feet and read letters on an eye chart. The smallest letters you can read at 20 feet will determine your visual acuity.

Acuity is expressed in values such as 20/40. A value of 20/20 indicates perfect vision, while any deviation needs correction. If you have a visual acuity of 20/36, it implies you need to be 20 feet to read something a person with perfect vision can read when standing 36 feet away.

Children require different methods of measuring visual acuity, usually relying on identifying shapes.

Keratometry

Using a keratometer, your doctor measures the contour of the front part of your eye by focusing light on the cornea and determining the angle of reflection. Keratometry differentiates between regular and disease-induced astigmatism while helping determine the type of correction required.

Refraction

Your provider uses a phoropter to place a series of lenses in front of your eye and asks you which one improves your vision the most. Refraction helps determine the best lens that corrects your vision problems.

What Do Astigmatism Measurements Mean?

Astigmatism is measured in diopters. If you have perfect vision, your diopters would be 0. Most people have astigmatism of 0.5-0.75, requiring no treatment. Higher diopters require glasses.

The last two values out of the three of your lenses prescription refer to astigmatism. Cylinder measures the degree of astigmatism in diopters, indicating how curved your cornea is overall. On the other hand, Axis shows the precise place on the cornea where the irregularity is located. Axis numbers range from 0 to 180.

Treatment

The mainstay treatment for all degrees of astigmatism is corrective lenses, either contact lenses or eyeglasses. However, very mild astigmatism with no other associated refractive defect may not need corrective lenses.

If you have astigmatism of 1.5 and above (moderate-high), you require glasses or contact lenses to see clearly. Eyeglasses usually contain a special cylindrical lens that compensates for the irregularity of the cornea. Both soft contacts and rigid-gas permeable contacts can correct astigmatism.

Orthokeratology is also a treatment option for astigmatism. It involves wearing specially-designed, rigid contact lenses that help reshape the cornea. You can wear the lenses overnight and remove them during the day. Even though orthokeratology can treat moderate astigmatism, discontinuation of retainer lens use causes relapse to the original state.

Laser surgery, including LASIK and PRK, offers a long-term treatment option for astigmatism. The doctor reshapes your cornea by removing some eye tissues helping you to see clearly. Talk to your doctor to determine if you are eligible for laser surgery. 

Can Astigmatism Be Cured?

Eyeglasses and contact lenses usually correct mild to moderate astigmatism by compensating for the unevenness in the curvature of the cornea or lens. But if you want a long-term solution, you can opt for LASIK surgery. Notably, you might need multiple surgeries to correct the defect if your astigmatism is severe. 

Prevention

The development of astigmatism is still not well understood, making its prevention impossible. Claims that reading in low light and sitting near a television can cause or worsen astigmatism are not true. Therefore, prevention strategies based on such myths are not effective.

FAQs

How can you tell if you have astigmatism?

Symptoms such as blurry vision at all distances, eyestrain, and headache are potential indicators of astigmatism. However, these symptoms also occur in other eye conditions. A comprehensive eye examination and testing is the surest way of determining whether you have astigmatism or not.

Does astigmatism go away?

Both hereditary and acquired astigmatism can worsen or improve with time. LASIK surgery is likely to cure the disorder, while the other treatment methods only improve your vision but do not cure astigmatism.

Do you need glasses for astigmatism?

Eyeglasses are one of the non-invasive methods of correcting astigmatism. However, if you do not want to wear glasses, you can choose contacts or laser surgery. Discussing with your doctor will help you determine the best treatment for your astigmatism.

References

1. What Is Astigmatism? (December 2021). American Academy of Ophthalmology.

2. The differences of corneal astigmatism in different populations and its quantitative analysis. (June 2020).  NCBI. 

3. Astigmatism. (June 2019). National Eye Institute.

4. What causes astigmatism? (July 1976).  Journal of the American Optometric Association. July 1, 1976.

5. What Do Astigmatism Measurements Mean? (April 2021). American Academy of Ophthalmology.

6. Astigmatism. American Optometric Association.