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Overview: What Is Astigmatism?
Astigmatism occurs when your eyeball has a slightly irregular curvature. This makes it so that your eye cannot focus light properly on the retina, resulting in blurry vision far away and up close. This condition is common and typically corrected with glasses, contacts, or surgery.
Other vision conditions (refractive errors) include myopia (nearsightedness), hyperopia (farsightedness), and presbyopia (age-related farsightedness). You can have a combination of different refractive errors, for example, myopia and astigmatism in one eye, and hyperopia plus astigmatism in the other eye.
Research shows that there is likely a genetic component involved in astigmatism and other eye health issues. Astigmatism may develop in infancy or later on in life.
Symptoms of Astigmatism
People with very mild astigmatism may not have any symptoms. If astigmatism worsens, you may notice vision problems such as:
- Blurry vision (distance or near)
- Glare or halos around lights
- Sensitivity to light
- Decreased night vision
- Shadows or ghosting of images
- Eye strain and fatigue (particularly while viewing digital devices)
Diagnosis & Types of Astigmatism
Astigmatism develops when the curvature of your eye is abnormal. This may happen for a few reasons:
- Corneal astigmatism occurs when the curvature of the cornea (the clear tissue on the front of your eye) is egg-shaped instead of spherical. This form of astigmatism is more common.
- Lenticular astigmatism occurs when the lens inside your eye changes in curvature, often in older age.
Most people have regular astigmatism. This means the two different curvatures of your eye are 90 degrees apart. Irregular astigmatism occurs when the cornea has more than two curvatures that are not 90 degrees apart.
Irregular astigmatism is not very common and may develop from an eye disease called keratoconus, which causes abnormal steepening and thinning of the cornea. Other causes include eye injury and complications from laser eye surgery.
The eye doctor can diagnose astigmatism by performing a few tests:
- Refraction is the part of an eye exam where you view an eye chart, while the doctor shows you different lenses and asks you which one looks clearer. This test helps the doctor determine your eyeglass prescription and uncovers whether you have myopia, hyperopia, or astigmatism by testing the way your eye bends (refracts) light rays.
- Keratometry measures the curvature of your cornea. This quick test allows the doctor to see if your cornea is flat or steep, and reveals how much corneal astigmatism you have. This measurement is typically used when the doctor fits you with contact lenses but is also helpful in diagnosing keratoconus.
- Corneal topography measures the surface of the cornea and gives the doctor a detailed, computerized map. This test is particularly helpful if your doctor suspects irregular astigmatism or corneal disease.
When To Get Glasses for Astigmatism
If you find yourself struggling with daily activities such as driving, reading, or computer work, consult your eye doctor. Some of the main symptoms that indicate you need correction for astigmatism include blurry vision, headaches, squinting, eye strain, and reduced night vision.
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Other signs you may need glasses include:
- Double vision
- Needing more light to read
- Losing your place while reading
- Distortion in your vision
- Halos when driving at night
The eye doctor can examine your eyes to ensure you do not have serious eye conditions that may cause similar symptoms.
Best Types of Glasses for Astigmatism
There are different types of materials used for your corrective lenses. They include, in order from thickest to thinnest:
- CR-39 (standard) plastic
- High index
Choosing the right type of lens for vision correction depends on the degree of astigmatism, along with any myopia or hyperopia correction. Generally, the higher your prescription, the thinner the lens you should choose. Thinner lenses also tend to be lighter, although Trivex material is lighter than high-index plastic.
When the eye doctor writes your eyeglass prescription, you should notice a number under the “cylinder” (CYL) section if you have astigmatism. This number indicates how much astigmatism you have, which is measured in diopters (D):
- Mild astigmatism is anything under 1.00 D. CR-39 plastic is suitable for mild prescriptions.
- Moderate astigmatism ranges from 1.00 to 2.00 D. Polycarbonate or Trivex are an excellent choice.
- Severe astigmatism ranges from 2.00 to 4.00 D. If your astigmatism is severe, polycarbonate, Trivex, or high-index lenses are ideal.
- Extreme astigmatism is anything above 4.00 D. High-index lenses are the best choice for strong astigmatism corrections.
Other tips for choosing eyewear for astigmatism:
- Anti-reflective coating helps to reduce glare off the surface of the lenses, particularly with high-index lenses.
- A flatter frame is generally better for higher astigmatism corrections. Some people have a hard time adapting to wraparound glasses with more curvature across the front of the frame.
- Some people take longer to adapt to astigmatism glasses. You may feel a little dizzy at first or notice some distortion, such as a fishbowl effect. If this sensation does not improve after several days, your eye doctor can determine if you need an adjustment in your prescription or the glasses.
Alternative Astigmatism Treatment Options
If you prefer not to wear glasses, there are other ways to treat astigmatism.
Astigmatism Contact Lenses
Contacts that correct astigmatism are available as:
- Soft contact lenses are excellent for low to moderate amounts of astigmatism. These lenses are soft and flexible, making them ideal for comfort. You will be prescribed special astigmatism lenses, called toric lenses, by your optometrist.
- Rigid gas-permeable (RGP) lenses are hard contacts. These tend to be less comfortable versus soft contacts, at least initially. However, most people find the vision is clearer with RGP lenses because they are better at correcting corneal astigmatism, particularly irregular astigmatism. Many keratoconus patients wear RGP lenses.
- Hybrid lenses are contacts that are hard in the center and soft around the edges. They provide the better vision of an RGP lens with the improved comfort of a soft lens.
LASIK Eye Surgery
LASIK is a form of laser eye surgery that corrects astigmatism, along with myopia or hyperopia. Typically, LASIK can treat up to 6.00 D of astigmatism. However, if your corneas are thin or you have a corneal disease (such as keratoconus), the surgeon may not be able to perform the procedure.
Other Refractive Surgeries
An alternative laser eye surgery is PRK (photorefractive keratectomy). Some people with thinner corneas or higher prescriptions are better candidates for PRK than LASIK.
Other refractive surgeries that correct astigmatism involve placing a lens implant inside the eye. A refractive lens exchange removes the natural lens inside your eye and replaces it with an intraocular lens implant (IOL). These steps are the same as cataract surgery.
The other type of surgery is called a phakic intraocular lens implant surgery. Instead of removing the natural lens, the surgeon leaves it in place and inserts an IOL in front of your natural lens. This IOL can be removed or replaced later.
Astigmatism Glasses FAQ
What level of astigmatism requires glasses?
If you experience any of these symptoms from astigmatism, you may require glasses to correct your vision: blurry vision, headaches, squinting, eye strain, reduced night vision, double vision, difficulty reading, distortion in your vision, halos when driving at night.
How do glasses work for astigmatism?
Corrective eyeglasses help bend the light passing through your eye to focus on the retina correctly to produce a sharper image.
What are the best glasses for astigmatism?
It depends on the severity of your astigmatism. If your astigmatism is severe, high-index, Trivex, or polycarbonate lenses are best. See an eye care professional for the most personalized recommendation.
What causes astigmatism to get worse?
For many people, astigmatism stays the same, or barely changes over time. Sometimes it does cause your vision to get worse with time. This depends on your corneal health and whether you have other eye conditions such as keratoconus.