Definition of Astigmatism
Astigmatism (uh-STIG-muh-tiz-um) is a common, mild and generally easily treatable imperfection in the curvature of your eye. The condition can cause blurred vision.
Astigmatism occurs when the front surface of your eye (cornea) or the lens, inside your eye, has a slightly different surface curvature in one direction from the other. Instead of being even and smooth in all directions, the surface may have some areas that are flatter or steeper.
Astigmatism blurs your vision at all distances. Astigmatism is often present at birth and may occur in combination with nearsightedness or farsightedness. Often it’s not pronounced enough to require corrective action. When it is, your treatment options include corrective lenses and surgery.
Symptoms of Astigmatism
Signs and symptoms of astigmatism may include:
- Blurred or distorted vision
When to see a doctor
If your quality of vision detracts from your enjoyment of activities or interferes with your ability to perform everyday tasks, see an eye doctor. An eye doctor can determine whether you have astigmatism and, if so, to what degree. He or she can then advise you of your options to correct your vision.
If you’re a healthy adult older than 40, have your eyes examined about every two to four years until age 55.
After age 55, have them checked every one to three years for signs of eye disease or problems and after age 65, every one to two years.
If you have eye problems, such as astigmatism, you may need to have your eyes checked more frequently. If you’re at risk of certain eye diseases, such as glaucoma, or you have diabetes, check with your doctor to see how often you need to have your eyes examined.
Your eye has two parts that focus images, the cornea and the lens. In a perfectly shaped eye, each of these focusing elements has a perfectly smooth curvature, like the surface of a smooth ball.
A cornea or lens with such a surface curvature bends (refracts) all incoming light the same way and makes a sharply focused image on the back of your eye (retina).
However, if your cornea or lens isn’t evenly and smoothly curved, then it causes light rays to be unevenly focused. This causes a refractive error. Astigmatism is a type of refractive error.
In astigmatism, your cornea or lens is curved more steeply in one direction than in another. You have corneal astigmatism if your cornea has a distorted shape. You have lenticular astigmatism if your lens is distorted.
Either type of astigmatism can cause blurred vision. Blurred vision may occur more in one direction, either horizontally, vertically or diagonally.
Astigmatism may occur in combination with other refractive errors, which include:
- Nearsightedness (myopia). This occurs when your cornea is curved too much or your eye is longer than normal. Instead of being focused precisely on your retina, light is focused in front of your retina, resulting in a blurry appearance for distant objects.
- Farsightedness (hyperopia). This occurs when your cornea is curved too little or your eye is shorter than normal. The effect is the opposite of nearsightedness. When your eye is in a relaxed state, light is focused behind the back of your eye, making nearby objects blurry.
Astigmatism may be present from birth, or it may develop after an eye injury, disease or surgery. Astigmatism isn’t caused or made worse by reading in poor light, sitting too close to the television or squinting.
Preparing for your appointment
You’re likely to start by seeing your family doctor or a general practitioner. However, in some cases when you call to set up an appointment, you may be referred to an eye doctor (ophthalmologist).
Because appointments can be brief, and because there’s often a lot to discuss, it’s a good idea to be well prepared for your appointment. Here’s some information to help you get ready for your appointment, and what to expect from your doctor.
What you can do
- Write down any symptoms you’re experiencing, including any that may seem unrelated to the reason for which you scheduled the appointment.
- Write down key personal information, including any major stresses or recent life changes.
- Bring a list of all medications, vitamins or supplements that you’re taking.
- Write down questions to ask your doctor.
Your time with your doctor is limited, so preparing a list of questions will help you make the most of your time together. List your questions from most important to least important in case time runs out. For astigmatism, some basic questions to ask your doctor include:
- What is likely causing my symptoms?
- Other than the most likely cause, what are other possible causes for my symptoms?
- What kinds of tests do I need?
- Is my condition likely temporary or chronic?
- What is the best course of action?
- What are the alternatives to the primary approach that you’re suggesting?
- I have these other health conditions. How can I best manage them together?
- Are there any restrictions that I need to follow?
- Should I see a corneal specialist?
- Are there any brochures or other printed material that I can take home with me? What websites do you recommend visiting?
In addition to the questions that you’ve prepared to ask your doctor, don’t hesitate to ask questions during your appointment at any time that you don’t understand something.
What to expect from your doctor
Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:
- When did you first begin experiencing symptoms?
- Have your symptoms been continuous, or occasional?
- How severe are your symptoms?
- What, if anything, seems to improve your symptoms?
- What, if anything, appears to worsen your symptoms?
Tests and diagnosis
To diagnose your condition, your eye doctor (ophthalmologist) may review your symptoms and conduct a comprehensive eye examination.
Your eye examination may include several tests, such as:
- Vision tests. Your doctor may ask you to read letters on a chart to test your vision in a visual acuity test.
Test to measure the curvature of your cornea. By measuring light reflected from the surface of your cornea, a device called a keratometer measures the amount of curvature to your cornea’s surface and can confirm the presence of astigmatism. This test is called keratometry.
The curvature of your cornea is an important piece of information for contact lens fitting. The curvature tends to be irregular in astigmatism.
To measure variations in corneal surface curvature, doctors may use a process called computerized corneal mapping. Computerized corneal mapping uses a keratoscope fitted with a video camera (videokeratoscope) to create a map of your cornea’s surface.
Test to measure light focus. To measure how your eyes focus light, your eye doctor may place different lenses in front of your eyes using a device called a phoropter.
Your doctor may also use a device called a retinoscope, which directs a beam of light into your eye, to determine how your eye focuses light.
These procedures can assess the degree of your refractive error and help calculate prescriptions for contact lenses and glasses.
Treatments and drugs
The goal of treating astigmatism is to address the uneven curvature that’s causing your blurred vision and improve your vision.
Treatments include corrective lenses and refractive surgery.
Wearing corrective lenses treats astigmatism by counteracting the uneven curvature of your cornea.
Types of corrective lenses include:
- Eyeglasses. Eyeglasses can be made with special lenses that help compensate for the uneven shape of your eye. In addition to correcting astigmatism, eyeglasses can also correct for other refractive errors, such as nearsightedness or farsightedness.
Contact lenses. Like eyeglasses, contact lenses can correct astigmatism. A wide variety of contact lenses are available, including hard, soft, extended wear, disposable, rigid, gas permeable and bifocal contact lenses. Ask your eye doctor about the pros and cons of each and which contact lenses might be best for you.
Contact lenses are also used in a procedure called orthokeratology. In orthokeratology, you wear rigid contact lenses for several hours a day until the curvature of your eye improves. Then, you wear the lenses less frequently to maintain the new shape. If you discontinue this treatment, your eyes return to their former shape.
Wearing contact lenses for extended periods of time increases the risk of infection in the eye.
This astigmatism-treatment method corrects the problem by reshaping the surface of your eye. Before surgery, doctors will evaluate you and determine if you’re a candidate for refractive surgery. Refractive-surgery methods include:
LASIK surgery. Laser-assisted in-situ keratomileusis (LASIK) is a procedure in which a doctor uses an instrument called a keratome to make a thin, circular hinged cut into your cornea. Alternatively, this same cut can be made with a special cutting laser.
The surgeon lifts the flap and then uses an excimer laser to sculpt the shape of the cornea under the flap. An excimer laser differs from other lasers in that it doesn’t produce heat.
- Photorefractive keratectomy (PRK). In PRK, your surgeon removes the outer protective layer of the cornea before using an excimer laser to change the curvature of the cornea.
- LASEK surgery. In laser-assisted subepithelial keratomileusis (LASEK) a much thinner layer of cornea is folded back, which makes your eye less vulnerable to damage should an injury occur. LASEK may be a better option if you have a thin cornea or if you’re at high risk of an eye injury at work or from playing sports.