Myopia is the refractive ametropia or a disorder, because of which the light rays are not focused on the retina but in front of it.
The practical consequence is that the observed objects tend to appear blurred, and the best viewing is limited only to those particularly close.
Classification of myopia
Myopia, like all the ametropia is measured in diopters: the correction can be used to slow, thanks to which the images come into focus on the retina. Indeed, imagine that the retina is the screen on which the image comes from a projector. In the short-sighted as if the image is on the screen becomes blurred, so you need to shift the focus back with an adjustment, so that we can see clearly.
The lens that allows to quantify the myopia is not mentioned, however, that both the lens which is then actually required, as are made small adjustments according to the subjective needs of the person and the type of corrective means (glasses or contact lenses). It is recommended, therefore, an optometric examination.
Myopia is generally due to an excessive length of the eyeball. Another cause can be altered curvature of the refractive surfaces of the eye. In the early and intermediate stages of cataract or in response to metabolic alterations can manifest myopia as a result of alteration of the refractive index of the ocular media, in particular of the lens.
In addition to this we can mention other optical classification mainly on the basis of evolutionary or hereditary cause.
The severity of myopia is measured in diopters (indicate the power of corrective lenses needed to compensate for the defect): up to -3.00 diopters of myopia is mild and considers himself a visual defect in an otherwise healthy eye, from -3.00 to -6.00 diopters of myopia is average, while a myopia greater than -6.00 diopters is considered of high degree. This is also known as pathological, as there is an increased risk of diseases such as ocular chorioretinal or retinal detachment or galucoma.
The myopic vision of the subject
Light rays passing through the optical eye (cornea, lens, etc.). Come into focus within the eyeball, but in front of the retina instead of on the retina. The consequence is that the remote point, that is the farthest point of the eye in which there is a clear vision without the use of accommodation, is placed at a finite distance with respect to infinity, as happens in an eye without defects of view , said emmetropic. The maximum distance at which a person is able to see clearly is inversely proportional to the degree of myopia. For example, a -2.00 diopter myopic unable to see clearly at most at 50 centimeters (ie half a meter) and not beyond. Instead, the subject myopic will be able to obtain a focus for points even closer compared to a subject emmetropic.
Treatment of myopia
At the end of the correction is preferable to use the term more suitable and adapted to various visual requests. The compensation of myopia involves the use of concave lenses negative, bearing the image plane on the retina. The lenses can be ophthalmic and then mounted on glasses or may be used in contact. The correction of myopia can also be performed with surgical techniques, usually by laser, which changes the curvature of the cornea, decreasing the refractive power of the cornea, compensating for myopia. The most used techniques are the PRK and LASIK. Other surgical treatments in use today are the installations of phakic lenses and replacement of the lens.
Among the methods of compensation, we can also mention the different techniques in order to relax the accommodation, but not correct myopia. In fact, the eye can simulate a functional myopia. This is because myopia, often linked to an intense use of the eyes at close range (reading, pc, work) you have a comorbid deficits such as accommodative inertia, excess and spasm. Several techniques allow to relax the accommodation. Among them, at the popular level, stands the Bates Method and it inspired methods that have given long-term results but have not yet been tested and approved by the medical establishment. With these methods it is possible to improve the ability to visualize and improve recognition in the case of blurred images, increasing visual acuity.