Astigmatism


Definition:

Astigmatism 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 part of the eye, the cornea, is not a regular symmetrical spherical shape. Instead, its shape is rather like that of the back of a spoon – longer in one direction than another. Because the cornea is an irregular shape, the eye can’t focus light passing through it sharply on to the back of the eye or retina. So vision is blurred 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.

Many people have some degree of astigmatism. In fact, it is rare to find a perfectly formed eye. Astigmatism appears to run in families and is often present from birth. If you have astigmatism, chances are good your children will have it also. It may worsen slowly over time but may remain fairly stable throughout life. Astigmatism often occurs with other vision conditions such as nearsightedness (myopia) and farsightedness (hyperopia.)

Symptoms:
Signs and symptoms of astigmatism may include:

*Blurred or distorted vision
*Headaches
*Eye strain
*Fatigue
*Blurred vision at certain distances

The most common symptom of astigmatism is blurred vision. Some people describe it as double vision but in only one eye. As a result of trying to focus on near or distant objects, a patient may develop eyestrain, squinting and headaches. Note the diagram at right – a person WITHOUT astigmatism would see all the radial lines as perfectly sharp and with the same contrast. The diagram  below illustrates how some lines might appear clearer than others to a person with astigmatism.

Children with astigmatism may be too young to notice or describe astigmatism. They may frown, squint, or pull objects close in an effort to get a clearer picture. They may also tilt or turn their head. This extra effort can lead to eyestrain, fatigue or reduced reading efficiency.

Causes:
As the eye develops in the womb, several factors determine the shape of it, including inherited genetic factors and environment. It would seem that these factors can lead to an irregular curvature of the cornea, although the exact cause isn’t known.

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, 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.

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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.

Test & Diagnosis :

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The Simple Astigmatism test :
1.If you have contacts or glasses, wear them.
2.Sit about 14 inches away from your computer screen.
3.Cover one eye.
4.Note how the lines and squares appear (for example, wavy or blurred).
5.Test the other eye in the same manner.

To a normal eye, the lines will appear sharply focused and equally dark. If some sets of lines appear sharply focused and dark while others are blurred and less dark, you may have astigmatism. Regardless of your result, see your eye doctor on a regular basis for a complete eye exam.

To diagnose astigmatism, your eye doctor may:

*Measure reflected light. By measuring light reflected from the surface of your cornea, a device known as a keratometer quantifies the amount and orientation of corneal astigmatism.
*Measure the curvature of your cornea. Using light to project rings on to your cornea, a device called a keratoscope measures the amount of curvature to your cornea’s surface and can confirm the presence of astigmatism. 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.

To measure the change in corneal surface curvature, a process called corneal topography is used. Corneal topography uses a videokeratoscope, which is a keratoscope fitted with a video camera.

Treatment:
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.

Corrective lenses
:
Wearing corrective lenses treats astigmatism by counteracting the uneven curvature of your cornea. Types of corrective lenses are:

*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 — hard, soft, extended wear, disposable, rigid gas permeable and bifocal. 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, 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 former shape. Wearing contact lenses for extended periods of time increases the risk of infection in the eye.

Refractive surgery;
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 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.

*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.

Conclusion:
If you experience a distortion or blurring of images at all distances — nearby as well as far — you may have astigmatism. Even if your vision is fairly sharp, headache, fatigue, squinting and eye discomfort or irritation may indicate a slight degree of astigmatism. A thorough eye examination, including tests of near vision, distant vision and vision clarity, can determine if astigmatism is present. Your eye doctor can answer any questions you may have about the various methods for correcting astigmatism and other vision problems.

Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose.
Resources:
http://www.bbc.co.uk/health/physical_health/conditions/astigmatism2.shtml
http://www.dcareaeyecare.com/astigmatism_article.html
http://www.mayoclinic.com/health/astigmatism/DS00230
http://www.lasersurgeryforeyes.com/astigmatism.html#Symptoms
http://www.webmd.com/eye-health/understanding-astigmatism-basics
http://www.jnjvision.com/thinking-whocanwear-test.htm

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