Refractive disorders include myopia, nearsightedness, hyperopia, farsightedness and astigmatism. Refractive disorders produce objects that appear out of focus. This is because the images from various distances are not clearly focused on the retina, or light sensitive area of the back of the eyeball. It is caused either by an eyeball that is too long or too short or by a lens that cannot focus adequately. In myopia, objects at a distance appear out of focus, In hyperopia, closely held objects are blurred. In astigmatism, abnormal curvature of the cornea leads to distortions of certain portions of vision. Glasses, contact lenses and corrective surgery, allow the images to be properly focused on the retina.
Causes of Myopia
Development of the eyeball is the principal cause. Hereditary factors contribute to slight mismatches of eye length and focusing power.
Signs and Symptoms of Myopia
Myopia produces blurred vision for distant objects. Hyperopia leads to blurred close objects. Astigmatism produces blurriness or portions of the objects that correspond to the deformed part of the cornea. All of these may produce eyestrain and headaches.
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Medical Content Last Updated on 07/12/2008
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