Near sightedness Myopia


 
 
Concept Explanation
 

Nearsightedness Myopia

Nearsightedness (Myopia):

Nearsightedness is a defect of vision due to which a person is not able to see distant objects clearly. This defect is also called shortsightedness or myopia. It arises mainly due to two reasons.

  • In certain people, the eyeball becomes elongated, i.e, longer than the normal eye. As a result, the distance of the retina from the crystalline lens increases. Then, even for the maximum focal length of the eve-lens, ie., when the cilliary muscles are most relaxed, Parallel rays of light from far away objects get focused at a point before the retina as in  Figure (a).
  •  In some cases, the curvatures of the cornea or the lens are such that the eye-lens has a shorter focal length (more power) than usual. In such cases also, the image forms short of the retina. In both cases, far away objects cannot be seen clearly, although nearby objects can.
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    Sample Questions
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    Question : 1

    Which of the following are correct ?

    (a) Nearsightedness is a defect of vision due to which a person is not able to see distant objects clearly this defect is also called shortsightedness .

    (b) The curvatures of the cornea or the lens are such that the eye-lens has a shorter focal length than usual causes nearsightedness

    (c) To correct nearsightedness the focal length of the concave lens is so chosen that divergent rays entering the eye focus on the iris and they appear to come from the far point of the unaided myopic eye .

    Right Option : A
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    Question : 2

    Which of the following are correct :

    (a) Near-sightedness is a defect of vision due to which a person is not able to see distant objects clearly.

    (b) Concave lens is used to correct nearsightedness.

     

    Right Option : C
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    Question : 3

    Which glasses or lens are used to correct the short sighted eye defect ?

    Right Option : A
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