Astigmatism is a common,
mild and 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
Signs and symptoms of astigmatism may include:
* Distortion in portions of your visual field
* Blurred 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 the degree of your astigmatism and
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 65. After age 65, have them checked
every one to two years for signs of eye disease or problems. 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
However, if your cornea or lens isn't evenly and smoothly curved, the
light rays aren't refracted properly. This causes a refractive error.
Astigmatism is one type of refractive error. In astigmatism, your cornea
or lens is curved more steeply in one direction than in another. When
the cornea has a distorted shape, you have corneal astigmatism. When the
lens is distorted, you have lenticular astigmatism. 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.
In most instances, astigmatism is present at birth. Sometimes,
astigmatism develops 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.
Tests and diagnosis
Your eye doctor may use these tools in examining your eyes:
* Keratometer. This instrument quantifies the amount and orientation
of corneal astigmatism by measuring reflected light from the surface of
Keratoscope and videokeratoscope. These devices are used to detect
and quantify corneal surface curvature and the presence of astigmatism.
A keratoscope uses light to project rings on your cornea. Observation
through the keratoscope of the reflection of light from your cornea and
inspection of the shape and spacing of the rings provide information
about the degree of astigmatism.
A keratoscope fitted with a video camera is called a
videokeratoscope. A videokeratoscope is the most common instrument used
to measure the change in corneal surface curvature, in a process called
Treatments and drugs
The goal of treating astigmatism is to address the uneven curvature
that's causing your blurred vision. Treatments include wearing
corrective lenses and undergoing refractive surgery.
Wearing corrective lenses treats astigmatism by counteracting the uneven
curvature of your cornea. Types of corrective lenses are:
* Contact lenses. Contact lenses can correct both corneal and
lenticular astigmatism. A wide variety of contact lenses are available —
hard, soft, extended wear, disposable, rigid gas permeable and bifocal.
Ask your eye doctor about their pros and cons and which contact lenses
might be best for you. Contact lenses are also used in a procedure
called orthokeratology, or Ortho-K. 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
* Eyeglasses. An alternative to contact lenses is eyeglasses. Like
contact lenses, eyeglasses help compensate for the uneven shape of your
This astigmatism treatment method corrects the problem by reshaping the surface of your eye. 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
* 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.
* Laser-assisted subepithelial keratomileusis (LASEK). In this
procedure, 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.
Radial keratotomy is a procedure that was used in the past to correct
astigmatism. However, it's not commonly performed anymore.