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Thursday, December 18, 2014

Myopia Definition - What Causes Myopia ?

What is myopia ?


Myopia or nearsightedness is a ametropia which the person (called a myopic) objects far away can not see clearly, but objects nearby. Hence the name (closed) myopia. An object with a convergence of 0 will not be sharply observed and as the object gets closer to the convergence will drop to a negative number. Once this number equals the object will be perceived sharply to the degree of ametropia.

General


Myopia is not a disease but a refractive error in the optical system of the eye. The property ensures that the lens depends on the distance to the object is stretched, so that the projected image is in focus on the retina. Reduced accommodation capacity, a too long eye or slightly flatter eye causes the image is sharp projected before the retina. Thus, the eye length, the lens of the eye is too long and too strong.

The deviation starts usually develop from 8 to 12 years and in the teenage years it gradually grows as the eye and thereby increases the eye length. The focal point within the eye will then go further out in front of the retina located. When maturity is reached, the refractive error usually remains stable.

The layout of eye diseases - such as training and farsighted - and their explanation and correction were devised by Franciscus Donders. The strength of the refractive error is measured by an optician, optometrist or ophthalmologist. It is expressed in the diopter of the necessary lenses. The higher the refractive error, the closer the object is to be held to be keenly observed.

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Myopia causes


The causes of myopia are diverse. The huge increase in myopia the last half century, according to some suggesting that overuse of the eyes at close range (computing, reading) often leads to myopia. According to the ophthalmologist William Bates was not the cause of myopia, the lens, but the deformation of the eyeball by the external eye muscles; theories are, however, generally be rejected by scientists.

Myopia is hereditary. CREAM (Consortium for Refractive Error and Myopia), a partnership between all myopiestudies worldwide, identified 26 genes for myopia and refractive errors. These genes have various functions, such as transmission of signals in the brains at the eyes, build-up of the connective tissue in the eye and development of the eye. Carriers of several of these genes have a 10 times higher risk of myopia.

In addition to genetic factors, environmental factors also play an important role. Many read or the extent to which a person as a child played outside, cause or aggravate symptoms in people who are already tainted. We also see that people with a higher education (eg university) is more common myopia.

Device


Glasses or contact lenses with concave lenses (with a negative strength) ensure that the rays are deviated so that they come together again on the retina. This can also be achieved by burning with a laser 4 to 8 scratches in the cornea, so that the lens is less convex. To laser surgery, however, are risks and it is still not clear what the effects are long term.

If the refractive error is very large, the usual correction means can be a problem. Glasses are then very thick at the outer edge and contact lenses are not tolerated by everyone. Then there are surgical options. An intraocular lens can be used without cataract operation and thus make the glasses or contact lens unnecessary. In an "early" cataract surgery, a so-called. Clear Lens Extraction And Replacement (CLEAR), the lens is replaced by an artificial lens. That can cause the accommodation capacity is lost, causing a correction means remains necessary, although much less than before the operation. This is done in most cases with a multifocal spectacles.

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