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Definition of Astigmatism

Definition of astigmatism
Light penetrates the eye thanks to the corneal membrane located on its surface. Astigmatism is an abnormality of the cornea, instead of being perfectly round (eg as a ping-pong ball cut in half), is oval (like the back of a teaspoon). The result is a distortion of the light that enters the interior of the eye and diffuse abnormally (visual distortion): the light rays entering the eye are net in one direction but scrambled in another. This disorder of the light scattering is called by doctors refractive error.

Causes and mechanisms of astigmatism
No cause of astigmatism is unknown, but the disease may be hereditary. Some causes are mentioned, such as an incorrect position or repetition of work in near vision.

No cornea is perfectly round, considering that each individual has a minimum astigmatism. Astigmatism is often associated with other disorders such as myopia or hyperopia.

In a normal eye with a perfectly smooth and spherical cornea (the same curvature in all directions), the light rays pass through and are directed at a single point on the surface of the retina.

If the cornea astigmatism is not perfectly spherical, and the failure of curvature deflects the light rays not at one point but at several points on the retina. The image interpreted by the brain is distorted.
Depending on the projection points of light from the retina, we speak of a part of hyperopic astigmatism (the focus behind the retina) or myopic (the focal front of the retina), and secondly to astigmatism simple (the curvature of the cornea is deformed along an axis that), compound (the curvature of the cornea is deformed along two axes) or mixed (a focal length is in front of the retina and the other in reverse).

Signs and symptoms of astigmatism

Symptoms of astigmatism are generally small. It manifests itself by a distortion of objects and sometimes eyestrain (with redness and headaches).

These signs majorem during a prolonged visual effort, whether near vision or far. More rarely, the astigmatism can see double the affected eye, it is called monocular diplopia.

Astigmatism Prevention

With what should we be confused?
It should not be confused with other refractive errors related to the shape of the eye, the main ones being:
myopia (eye too converge to its length or too long for its power, with an image of the observed object that forms in front of the retina): good near vision but no further;

hyperopia (not enough eye converge to its length or too short for its power, with an image that is formed behind the retina): good distance vision but not near;

presbyopia (loss of ability to focus, that is to say, the power of convergence of the eye, age related): close objects are blurred, forcing them away.

Is there a prevention possible?

Although some cases have been mentioned (incorrect position, repeat work near vision ...), no prevention is effective in astigmatism. The only prevention is the early detection of visual disturbances. In case of blurred vision, eyestrain or headaches or headaches, eye control is required.

Astigmatism Preparing consultation

When to consult?

If symptoms or visual fatigue, eye examinations can detect disturbances in visual acuity and refraction, including astigmatism.

However, if symptoms such as the appearance of a halo, or intensity differences of scintillating points, it is necessary to consult urgently because they evoke other diseases (glaucoma, cataracts, retinal abnormalities ...).

What is the doctor?

The ophthalmologist confirmed the diagnosis of astigmatism. It can measure the value and the axis of astigmatism with several devices (ophthalmometer Javal, retinoscopy and now use automatic refractometers).

It prescribes any necessary correction by glasses or contact lenses, or even a definitive surgical treatment.

Glasses and contact lenses are equipped with an additional component called a toric lens, whose function is to refract light and counteract the effects of astigmatism.

Refractive surgery corrects astigmatism by abrading (photoablation) surface the cornea (excimer laser keratotomy). A thin portion of the cornea is removed, to give it a spherical shape and to enable it to properly refract light.

This surgery is often reserved for astigmatism astigmatism strong and / or when combined with myopia.

How to prepare my next visit?

It is important to clarify the circumstances in which your vision problems appear: the end of the day, read closely ... This information will guide the ophthalmologist in his exams. Given the time of appointment, anticipate and do not wait for the troubles worsen consult.

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