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Question
Give Reason:
Deficiency of vitamin A causes night blindness.
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Solution
Because the visual purple (Rhodopsin) of the rods is not formed in the absence of vitamin A.
RELATED QUESTIONS
What is myopia?
What is the far point and near point of the human eye with normal vision?
What is the other name for
myopia
Name the defect of vision which makes the eye-lens cloudy resulting in blurred vision.
Name one defect of vision (or eye) which cannot be corrected by any type of spectacle lenses.
Name the body part with which the terms myopia and hypermetropia are connected.
A young man has to hold a book at arm's length to be able to read it clearly. The defect of vision is:
(a) astigmatism
(b) myopia
(c) presbyopia
(d) hypermetropia
Describe the mechanism of focusing the image of a distant object in your eye when you raise your head after reading a book.
Rewrite the following table so as to match second and third column with first column.
|
Column I
|
Column II
|
Column III
|
|
(i) Myopia
|
Old age problem
|
Bifocal lens
|
|
(ii) Presbyopia
|
Nearsightedness
|
Concave lens.
|
A person is unable to see clearly a poster fixed on a distant wall. He however sees it clearly when standing at a distance of about 2 m from the wall.
- Draw ray diagram to show the formation of image by his eye lens when he is far away from the wall.
- List two possible reasons of this defect of vision.
- Draw ray diagram to show the correction of this defect using appropriate lens.
