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Overview: What is Astigmatism?
Astigmatism refers to a common eye condition that causes your vision to be blurry at all distances—both near and far—because the curvature of your cornea (the clear front cover of your eye) or natural lens is irregularly shaped. This refractive error occurs because your eye cannot focus light properly, directly onto your retina, the light-sensitive surface that lines the back of your eye.
If your cornea is shaped more like a football than a soccer ball, your eye won’t be able to focus light rays at a single point. If the eye’s lens curvature changes, this can worsen your astigmatism. This can happen in adulthood and with naturally occurring cataracts.
There are three different types of refractive errors, including astigmatism:
- Myopia (Nearsightedness) — This occurs when your eye focuses light in front of the retina, so you have trouble seeing objects that are far away.
- Hyperopia (Farsightedness) — This occurs when your eye focuses light behind the retina, so you have trouble seeing objects that are nearby.
- Astigmatism — This occurs when your eye focuses light at different points both in front of and behind the retina, so you have trouble seeing objects both far away and close up.
You can inherit corneal errors like astigmatism through your genetics or develop it after an eye injury, eye surgery, or eye disease like keratoconus, which causes your cornea to form into a conical shape. Keratoconus is an eye disease that causes irregular and often high amounts of astigmatism.
Effects of Astigmatism on Visual Impairment
Whether you’re born with it or it develops later in life, the symptoms of astigmatism generally include the following:
- Blurry vision
- Trouble seeing objects both close up and far away
- Fluctuating vision
- Eye strain
- Difficulty seeing at night
- Seeing glare and halos at night
- Seeing shadowy images
If you only have a mild case of astigmatism, you may not notice any of the above symptoms or require correction. However, if you do need treatment, options are available, including corrective eyeglasses, contact lenses, and refractive surgery.
If you leave it alone, astigmatism can get better or worse over time. If you have vision problems, you should see your eye doctor to take an eye exam and discuss your options to help you achieve clear vision.
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5 Types of Astigmatism
Astigmatism can be broken down into five categories. Here’s what you should know about each of them:
1. Simple Myopic Astigmatism
Simple myopic astigmatism refers to when the light hits two focal points: one before the eye’s retina and one on the eye’s retina.
2. Simple Hyperopic Astigmatism
Simple hyperopic astigmatism happens when light comes to two focal points: one directly on the eye’s retina and one behind the eye’s retina.
3. Compound Myopic Astigmatism
Compound myopic astigmatism happens when the light hits two focal points at two different locations in front of the eye’s retina.
4. Compound Hyperopic Astigmatism
Compound hyperopic astigmatism refers to when the light comes to two different virtual locations behind the eye’s retina.
5. Mixed Astigmatism
Mixed astigmatism happens when rays of light hit two focal points: one before the eye’s retina and one behind the eye’s retina.
Astigmatism Severity Scale
Not all astigmatism is the same. Astigmatism can vary in severity. The degree of astigmatism is measured in diopters. For context, a perfect eye that has no astigmatism has 0 diopters, but some people have between 0.5 and 0.75 diopters of astigmatism. People who have about 1.5 or more diopters of astigmatism usually opt to have corrective treatment such as glasses, contacts, or eye surgery.
There are three numbers on any glasses or contact prescription, and the last two refer to astigmatism. Spherical indicates whether you are nearsighted (a minus sign) or farsighted (a plus sign). Cylinder measures the severity of astigmatism. Axis measures where astigmatism is located in degrees from 0 to 180.
Mild Astigmatism: < 1.00 diopter
Nearly 33 percent of Americans have astigmatism to some degree. Mild astigmatism is considered normal. Most people have it and do not need corrective lenses or surgery to see clearly. You may not even notice any symptoms with a mild case of astigmatism.
Moderate Astigmatism: 1.00 to 2.00 diopter
Moderate astigmatism is a little more serious and generally requires corrective lenses or laser surgery in order for you to see clearly. While you may be able to get by without wearing glasses or contacts, chances are that you will notice the symptoms of moderate astigmatism and glasses and contacts can certainly help.
Severe Astigmatism: 2.00 to 3.00 diopter
Severe astigmatism can cause serious symptoms that affect your day-to-day functioning. Blurred vision from severe astigmatism can give you headaches that can take a toll on your health.
Extreme Astigmatism: > 3.00 diopter
Extreme astigmatism will require treatment so that you can see objects both near and far with ease. If you do not treat extreme astigmatism, you will not be able to see clearly at all.
What Level of Astigmatism Requires Glasses?
Because most people have mild astigmatism, wearing glasses or other astigmatism treatment is not typically necessary unless you have moderate astigmatism or worse.
Again, it’s important to schedule regular checkups with an optometrist because astigmatism can change over time. If you wear glasses, you need to be sure that your prescription stays correct. And, if you don’t wear glasses because you don’t need them now, it’s still important to pay attention to your eye health in case you develop worse astigmatism later on.
Can LASIK Fix Astigmatism?
Yes, LASIK (laser in situ keratomileusis) and PRK (photorefractive keratectomy) can fix astigmatism. LASIK removes the tissue from the inner layer of the cornea with an excimer laser, and PRK removes it from the superficial and inner layers of the cornea. Both types of laser surgery permanently fix the shape of your cornea so you do not need to wear eyewear for clear vision.
In LASIK surgery, the LASIK surgeon will use a mechanical microkeratome (a blade) or a femtosecond laser to cut a flap in your cornea. They’ll leave a hinge at one end of the flap and fold it back to reveal the stroma (the middle section of the cornea). They’ll then use pulses from a computer-controlled laser to vaporize a portion of the stroma and replace the corneal flap.
While this may sound painful, the LASIK procedure only takes about 10 minutes per eye — and the laser itself only takes about 20 to 50 seconds to correct your vision, depending on how much correction you need.
It’s important to note that, while LASIK will fix your astigmatism, other refractive errors and vision changes can also develop over time. Because your eyes change over the course of your lifetime, you may experience new refractive errors after LASIK surgery. This is not a result of regression following the surgery. LASIK only treats existing conditions.