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Astigmatism

Definition


Disease: Astigmatism Astigmatism
Category: Eye diseases
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Disease Definition:

Astigmatism, which can cause blurred vision, is a common, mild and easily treatable imperfection in the curvature of the eye.

Often, astigmatism is present at birth, but because it’s not pronounced enough, it doesn’t require corrective action. This condition can also occur in combination with nearsightedness or farsightedness. However, corrective lenses and surgery are the treatment options available in case it is evident.

When the front of the cornea or the lens inside the eye has a slightly different surface curvature in one direction from the other, astigmatism occurs. The surface may have some areas that are steeper or flatter instead of being even and smooth in all directions.

Work Group:


Prepared by: Scientific Section

Symptoms, Causes

Symptoms:

Astigmatism has these signs and symptoms:
-    Blurred vision
-    Headaches
-    Distortion in portions of the visual field
-    Eyestrain

A person should consult an eye doctor in case the quality of their vision reduces their enjoyment of activities or even interferes with their ability to perform everyday tasks. The degree of astigmatism could be determined by an eye doctor, who can also advise the person of the treatment options that are available for them to correct their vision.

A person should have their eyes examined every two to four years in case they're older than 40 and healthy, until they reach 65, but they should have them checked every one or two years in case they've reached the age of 65 for signs and symptoms of eye disease or problems. A person may also need to have their eyes checked more frequently in case they have astigmatism or other eye problems.

A person should check with their doctor to see how often they need to have their eyes examined, in case they have diabetes or they're in risk of having certain eye disease, such as glaucoma.

Causes:

In a perfectly shaped eye, each of the parts that focus images, namely the cornea and the lens, has a perfectly smooth curvature just like the surface of a smooth ball. All incoming light is bended by the curvature surface of the cornea or lens the same way and a sharply focused image is made on the back of the eye (retina).

But the lights aren’t refracted properly in case a person's cornea or lens isn’t evenly and smoothly curved, which causes a refractive error. In this condition, the cornea or lens is curved more steeply in one direction than in another. A person will have corneal astigmatism in case their cornea has a distorted shape, and they will have lenticular astigmatism in case their lens is distorted. Either type of astigmatism can cause blurred vision, which can occur more in one direction, either diagonally, vertically or horizontally.

Astigmatism, which is one type of refractive error, can occur in combination with other refractive errors, such as:

Hyperopia (farsightedness):
Light is focused behind the back of the eye when the eye is in a relaxed state, causing nearby objects to be blurry. This condition occurs in case a person's eye is shorter than normal, or if their cornea is curved too little.

Myopia (nearsightedness):
In this condition, light is focused in front of the retina, instead of being focused precisely on it, resulting in a blurry appearance for distant objects. This condition occurs when the eye is longer than normal, or if the cornea is curved too much.

Although in some cases astigmatism can be developed after an eye injury, surgery or disease, but in most cases, it is present at birth. Reading in poor light, squinting or sitting too close to the television aren’t some of the reasons that cause astigmatism.

Complications

Complications:

Not available

Treatments:

Addressing the uneven curvature that is causing a person's blurred vision is the main goal of treating astigmatism. Wearing corrective lenses and undergoing refractive surgery are some of the treatments available.

CORRECTIVE LENSES.
Counteracting the uneven curvature of the cornea is how corrective lenses treat astigmatism. Some of the types of corrective lenses include:

Contact lenses: There is a very wide variety of contact lenses available, including soft, hard, disposable, rigid gas permeable, bifocal and extended wear. These contact lenses have the ability to correct both corneal and lenticular astigmatism. A person should ask a doctor about which type might be best for them; they should also talk about the pros and cons of contact lenses. There is a procedure called orthokeratology, in which the person wears rigid contact lenses for a few hours a day, until the curvature of the eye improves, and then they start wearing them less frequently in order to maintain the new shape. However, their eyes will return to their former shape whenever they stop using those lenses.

Eyeglasses: Eyeglasses could be used as an alternative to contact lenses, because they can also help compensate for the uneven shape of the eye.

REFRACTIVE SURGERY.
By reshaping the surface of the eye, this treatment method can correct the problem. Some of these surgeries are:

Radial keratotomy.
Although this procedure was used in the past to correct astigmatism, but these days, it’s not commonly performed.

PRK (photorefractive keratectomy).
In this surgery, the outer protective layer of the cornea is removed and an excimer laser is used to change the curvature of the cornea.

LASEK (laser-assisted subepithelial keratomileusis).
This type of surgery is the best option in case someone has a thin cornea, or if they're at a high risk of an eye injury at work or from playing sports. In this procedure, a much thinner layer of cornea is folded back, making the eye less vulnerable in case of an injury.

LASIK (laser-assisted in-situ keratomileusis) surgery.
In this procedure, a device called a keratome is used to make a thin, circular hinged cut into the cornea. But in some cases, the same cut could be made with a special cutting laser. After making the cut, the flap is lifted and an excimer laser is used to sculpt the shape of the cornea under the flap. There is a huge difference between an excimer laser and other types of lasers, because this kind of laser doesn’t produce heat.

Prognosis:

Not Available

Expert's opinion

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