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What is vision?25.08.2010р.
It is correct to count sight feeling or sensory sense. In medicine determine sight as ability to perceive the location of objects and objects in space in form appearance or image. A man and zoons possess optical sight, although there are other types of perception of outward things – for example, ultrasonic feeling which is possessed by bats.
Eyes, as well as any other organ of man, can execute the functions wrong, the defects of sight can develop. What is normal sight? It is here supposed to remember that an eye is the biological optical system, consisting of lenses. Every lens has focal distance – distance on which after a refraction in the lens of light rays his clear image proeciruetsya from a remote object.
Focal distance – a size is permanent, and it depends from the radius of curvature of lens. For a healthy eye focal distance is equal to distance between two lenses, that between a cornea and retina, that averages 23,5-24 mm. At such focal distance an eye possesses normal sight. Otherwise speaking, the normal is consider sight at which an image is mapped strictly to the retina of eyeball.
Light ray, passing at first through a cornea, after through the lens of the eye, tests a refraction and focuses on a retina. The refraction of light ray is named a refraction. General force of refraction is measured in diopters. When a refraction takes place correctly, an image on a retina focuses expressly.
Violation of refraction results in development of defects of sight: to myopia, long sight, astigmatism. It is widespread parafunctions eyes – over 30 % people suffer one or another violations of refraction.
Astigmatism more Frequent than all astigmatism is innate and shows up in early age, however reasons of his origin can be traumas of eyes, operations on an eyeball, serious psychical disorders.
At it sphericity of cornea is violated: in different meridians the refraction of light rays takes place with different force, as a result an object proeciruetsya not as a dot pattern, but as a direct cutting-off. Otherwise speaking, a man visile perceives objects in the distorted kind, thus he sees one contours enough expressly, and other abstrusely.
Interestingly, that astigmatism is developed at most people, however very small he is and does not interfere with clear perception of objects. As a rule, these people and unaware of such violations, even if regularly visit an ophthalmologist. The point is that a standard eye test can not expose small astigmatism, as for his diagnostics more deep computer inspection is needed. |
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