Defect of vision

For healthy eye lens becomes sufficiently thick when viewing near object and becomes properly thin for far objct. Due to age factor and other causes lens of eye cannot focus far and near objects clearly. There are two major defects on eye relating to focusing of lens

• Short sightedness or Myopia: On this defect one can see near object clearly but difficult to see far object. In this defect lens can be thick as required but cannot be thin properly for far object viewing. To overcome this defect spectacle with proper concave lens should be used as shown in fig below.
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• Long sightedness or Hyperopia: On this defect one can see far object clearly but difficult to see near object. In this defect lens can be thin as required but cannot be thick properly for near object viewing. To overcome this defect spectacle with proper convex lens should be used as shown in fig below.
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Along with above two defects, human eye may have following more defect.

• Coma
• Astigmatism
• Color Blindness