Name three common defects of vision. What are their causes? Name the type of lens used to correct each of them.
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https://www.meritnation.com/ask-answer/question/name-the-two-major-defects-of-vision-explain-their-causes-a/human-eye-and-colourful-world/1639896
https://www.meritnation.com/ask-answer/question/name-the-two-major-defects-of-vision-explain-their-causes-a/human-eye-and-colourful-world/1639896
Presbyopia is a common defect of vision which generally occurs at old age. A person suffering from this type of defect of vision cannot see nearby objects clearly and distinctively.
Presbyopia is caused by the
(i) weakening of the ciliary muscles
(ii) reduction in the flexibility of the eye lens
A person with presbyopia cannot read letters without spectacles. It may also happen that a person suffers from both myopia and hypermetropia. This type of defect can be corrected by using bi-focal lenses. A bifocal lens consists of both convex lens (to correct hypermetropia) and concave lens (to correct myopia).