Human Vision Defects,What is 20/20 Vision?

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Visual Defects

What does 20/20 Vision mean?

Visual acuity is expressed as a fraction. The top number refers to the distance you stand from the chart. This is usually 20 feet. The bottom number indicates the distance at which a person with normal eyesight could correctly read the line with the smallest letters. Normal vision is considered 20/20. If your vision is 20/40, the line you correctly read at 20 feet could be read by a person with normal vision at 40 feet. Of course, just because 20/20 vision is normal doesn't mean it's perfect. A small percentage of the population is blessed with vision better than 20/20, and just recently researchers unveiled corrective lens that offered vision closer to 20/10.


Causes of Myopia

Nearsightedness or myopia occurs when light entering the eye focuses in front of the retina instead of directly on it. This is caused by a cornea that is steeper, or an eye that is longer than a normal eye.

Nearsighted people typically see well up close, but have difficulty seeing far away. Near-sightedness usually becomes progressively worse through adolescence and stabilizes in early adulthood. Myopia is also known to be an inheritable defect.

Effects of Myopia

The effects of myopia can range depending on the severity of the problem, but usually the person would find it difficult to see long distances as it would be blurry, and also squinting appears to make things clearer.


The treatment for nearsightedness depends on several factors such as the person's age, life style. Vision can corrected with glasses which bend the light causing the focal point to be located of the retina, contacts lenses which work the same as glasses, laser surgery and convention surgery which alter the shape of the cornea.


Causes of Glaucoma

Glaucoma is...