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Vision defects

The basic condition of good and acute vision is a correct structure and functioning of visual system. In normal human eye light rays getting into the eye go through the cornea and lens and while focusing on the retina they are received by nerve receptors and transformed into electric impulses, which are then transmitted by optic nerves to the brain. The brain transforms the impulses into a distinct image. In the normal eye the cornea and retina parameters are adjusted to eye ball length, which ensures the focusing of light rays on the retina.



We can distinguish three classic vision defects:

NEARSIGHTEDNESS - Myopia


The eye ball of the myopic eye is prolated and light rays focus before instead of on the retina. Such an eye is incapable of acute vision of far objects.



FARSIGHTEDNESS – Hyperopia

The hyperopic eye is incapable of acute vision of near objects, which is caused by focusing of light rays behind the retina. The eye ball of the hyperopic eye is shorter.
One has to distinguish between hyperopia and presbyopia being a senile hyperopia, which often deteriorated with age and is caused by natural process of losing accommodative capabilities of the lens.



ASTIGMATISM


Astigmatism is caused by irregular curvature of the cornea. Light rays focus on various points, which results in a blurred vision. Astigmatism often occurs jointly with nearsightedness or farsightedness.
Last Updated on Tuesday, 26 April 2016 10:06