what is an astigmatism

what is an astigmatism

Astigmatism is a condition of the eye that causes either blurred vision or a feeling that each eye sees a slightly different objects. A structural problem - usually an unevenly curved cornea or lens - causes light entering the eye does not focus properly. This disorder is quite common, affecting about 30% of people to some extent. Treatment is not always needed, but when the problem is severe, prescription glasses or surgery can help improve the vision of the person.


The human eye is usually a perfectly round sphere. The light that enters the eye is focused by the cornea and the lens onto a point on the retina where the image is detected and communicated to the brain. In an attack astigmatism person, cornea or lens is not perfectly round; Often it is more like a form of football. When the eye is not bent properly, the light coming into the eye can not focus on a single point, which causes image blur.

Astigmatism is a type of refractive error, which means that the eye does not bend light into focus on the correct spot on the retina. Nearsightedness (myopia) and farsightedness (hyperopia) are refractive errors, caused by the cornea too curved or too flat, respectively. The eyes of people who are myopic focus the image before the retina, while in those who are farsighted focus behind her. People can have both astigmatism and other refractive error; it is estimated that 2/3 of the people who are nearsighted have another condition as well.


There are different types of astigmatism, as may be irregularly shaped portion of the eye, where the light is focused, and if the principal meridians of the eye are normal or not. This condition can be caused by a defect in either the cornea or the crystalline lens, although the type of the cornea is more common.

A normal eye focuses an image on a single point; Optometrists draw a more imaginary sign (+) at the center of the pupil, where the focus point should be. These are known as vertical and horizontal or main meridians. In an attack astigmatism person, the two meridians focus at the same point. If one focuses on the retina while the other does not, it is known as simple, while if both are focused either in front or behind the retina, it is known as a compound. One point ahead and behind is called mixed.

As with nearsightedness and farsightedness, the focus before the retina is called myopic and hyperopic behind. Therefore, if a meridian focuses in front of the retina while the other is on it, it would be called simple myopic astigmatism.

When the main meridians aligned perpendicularly - which means they meet at a 90 ° angle - it is known as the "regular" astigmatism. If the angle is off, it is called "irregular" and is a little more difficult to treat. The irregular type is often caused by an injury to the eye or a disease called keratoconus, in which the cornea takes a conical shape.


Astigmatism miners often go unnoticed, but severe cases can cause headaches, squinting and tired eyes, in addition to blurred vision. Most people with corneal irregularities were born with them, but may not notice any problems until they mature. Even those who have few symptoms can be diagnosed with this disease as part of a routine examination. Because many of the signs are not clearly or directly related to vision, people may find that the treatment improves headaches, they were not even really aware.


There are several ophthalmologic tests to determine the presence and level of astigmatism. Keratometer and a corneal topographer are instruments that can be used to measure the curvature of the cornea. A autorefractor can give an estimate of the ability of the eye to focus light properly. These instruments are non-invasive and most ophthalmologists and optometrists are able to detect even slight curvature problems during a review of the single view.

Sometimes astigmatism can be detected at home by covering one eye to look at an object, then change to cover the other eye. By going back and forth watching a single object or in a direction, the person may notice that the object appears to move, as if each eye sees a slightly different place. This usually indicates the presence of curvature of the cornea.


Glasses or contact lenses may be prescribed to treat most forms of astigmatism, but they usually do not correct the situation. Often two different lenses help the eyes to focus together, offsetting the unequal development. Glasses can not be used to treat people with the irregular shape, although some types of contact lenses can usually help. One type of contact lenses actually helps to reshape the eye; This treatment is called orthokeratology, or Ortho-K.

Surgical correction is an option for severe cases. A number of different procedures can be used to reshape the cornea of ​​the eye and make it more spherical. Laser in situ keratomileusis (LASIK) surgery uses a laser to sculpt the underside of the cornea after the upper part is raised. Keratectomy (PRK) and a similar technique called laser-assisted sub-epithelial keratomileusis (LASEK) remove or fold the very outer layer of the cornea and reshape the upper surface. An optometrist can help a patient to decide which method is a better option if surgery is recommended.

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