Astigmatism

Astigmatism is not a disease; it is simply a type of refractive error or vision condition that causes blurred, fuzzy, or distorted vision.

What Causes Astigmatism?

Astigmatism is a condition caused by small imperfections in how your eye bends light (a process called refraction) as it passes through the retina, the light-sensitive area at the back of the eyeball. The optic nerve transmits nerve signals from the retina to the brain, where they are converted into vision.

If your vision is functioning normally, the cornea and the lens behind it will refract light onto the retina. Unfortunately, imperfections in the curvature of the cornea or lens (or both) can prevent images from converging properly on the retina. The brain perceives these eye irregularities as unclear or distorted images.

Illustration by 529

Your cornea is a transparent dome covering the front surface of the eye. It curves like a lens on a telescope or camera. A perfectly curved cornea and natural lens will focus light signals onto the retina to create clear vision in the brain.

Unfortunately, the cornea and lens can have imperfect curves that hinder refraction, creating the blurred or distorted vision we call astigmatism. Irregularities in other structures in the eye can also contribute to astigmatism.

Symptoms of Astigmatism

Common signs and symptoms of astigmatism include:

• Squinting
• Blurred or distorted vision at all distances
• Poor night vision
• Double vision in one or both eyes
• Eye strain
• Headaches

Diagnosis

During a vision exam, an eye doctor will scan your eyeball to measure its entire surface in three dimensions. Parts of the eye called meridians help your eye doctor identify the high and low points on the cornea that cause astigmatism. A measurement called diopter estimates the degree of refraction occurring at each meridian.

The meridians of the eye look like a traditional clock face. For example, one meridian is the line connecting 6 (bottom) to 12 (top). Another meridian is the line connecting from 9 (left) to 3 (right).

The eye doctor assesses the differences between the meridians of the eye to determine the appropriate prescription that will create clear vision. Tests like retinoscopy involve shining a light into your eye while you look through different lenses until the doctor finds the lens that helps you see the clearest.

Read more: Astigmatism Test

Astigmatism in Children

Newborns often have astigmatism at birth, although this condition usually resolves within the first year. Very few children show signs of astigmatism by the age of 5 to 9 years.

However, some children may not outgrow astigmatism as they grow up, and uncorrected astigmatism can negatively affect learning and development.

Therefore, it is important to schedule regular eye exams for children to detect astigmatism and/or other uncorrected refractive errors.

Read more: Astigmatism in Children

Types of Astigmatism

Astigmatism has three main classifications, determined by the principal meridian (the steepest and flattest meridian of the eye).

• Myopic astigmatism: The principal meridian of the eye is myopic (myopia + astigmatism).
• Hyperopic astigmatism: The principal meridian is hyperopic (hyperopia + astigmatism).
• Mixed astigmatism: The principal meridian is both near and far (astigmatism is the primary refractive error).

You may also see astigmatism described as follows:

• Corneal: A defect in the cornea.
• Lenticular: A defect in the lens of the eye.
• Regular: The principal meridians are perpendicular to each other (90 degrees apart).
• Irregular: The principal meridians are not perpendicular (sometimes due to trauma and corneal scarring). Keratoconus, a condition where the cornea thins over time, and some forms of eye surgery can also cause irregular astigmatism.

Treatment of Astigmatism

Eyeglasses, contact lenses, and some eye surgeries like LASIK can correct astigmatism.

Eyeglasses

Prescription lenses correct refractive errors in the cornea and lens of the eye. According to the American Academy of Ophthalmology, common astigmatism can be corrected to 20/20, although astigmatism may be too severe to correct vision to normal levels. Irregular astigmatism often cannot be corrected to 20/20.

Contact Lenses

Many people choose to correct their astigmatism with contact lenses, which come in three main types:

• Toric. These soft contact lenses can have varying degrees of refraction tailored to each meridian of the eye, allowing for precise vision correction. Due to their complex design, toric contact lenses for astigmatism are often more expensive than other types.
• Gas permeable. These hard lenses have a uniform shape that essentially replaces the refractive effect of the cornea. They often provide sharper vision than softer toric lenses. Note that some gas permeable lenses use a toric design. Gas permeable lenses may not be as comfortable as original toric lenses but provide excellent vision correction and comfort over time.
• Hybrid. These lenses are hard in the center for higher visual clarity but soft at the edges for more comfort. They often provide the best of both worlds for correcting astigmatism with contact lenses. Hybrid and gas permeable lenses require more time and expertise to achieve the proper fit, so consider this factor when making a purchase decision.

Read more:

• Astigmatism Treatment
• Exercises for Astigmatism
• Contact Lenses for Astigmatism: Toric, GP, and Hybrid
• Contact Lenses for Astigmatism: Q&A
• What are bifocal contact lenses for astigmatism?
• Colored contact lenses for astigmatism

Astigmatism Surgery

Procedures that reshape the cornea and remove cataracts can correct astigmatism. For example, LASIK surgery uses highly precise laser beams to make the cornea more symmetrical and can permanently correct moderate astigmatism.

Furthermore, an eye surgeon can implant a toric intraocular lens (IOL) into the eye to correct astigmatism and remove cataracts at the same time.

Note that toric IOLs can be significantly more expensive if your health insurance does not cover this procedure. Surgery is permanent, so you must weigh the risks and ensure the doctor confirms that you are a suitable candidate for this surgery.

Each person's vision is different, meaning each type of astigmatism has its own impact. This means you must pay more attention to the fit and function of eyeglasses or contact lenses. And do not rush into surgery until you have thoroughly researched the topic and discussed it with your eye doctor.

Frequently Asked Questions

Q: How does astigmatism affect night driving?

A: Driving at night with uncorrected astigmatism can be a challenging task. This is because astigmatism causes light to scatter in the eye instead of focusing on a single point (the retina). Streetlights and traffic lights can have glare, halos, or streaks of light that distract those with astigmatism. This can negatively impact night driving.

Q: Can people with astigmatism wear contact lenses?

A: Yes, you can purchase contact lenses for astigmatism. There are three main options: Soft contact lenses, gas permeable lenses, and hybrid lenses. Each type of lens has different benefits, so it’s best to discuss with your eye doctor to find out which astigmatism contact lens is best for your condition.

Q: How are glasses for astigmatism different from other types of glasses?

A: Glasses for astigmatism are different from other types of glasses in that they have additional specifications for the lens power. Cylinder (listed as CYL on the vision prescription) indicates whether the lens needs additional power to correct astigmatism. A person with astigmatism will also have an AXIS specification indicating the degree of rotation of the astigmatism correction. A person without astigmatism will not have CYL or AXIS specifications.

The doctor will review all available treatment options with the goal of improving clear, comfortable, and effective vision.