Explain the two most common defect at vision explain with the help of ray diagram how the are corrected
Answers
They are myopia (short sight) and hypermetropia (long sight)
myopia : this is a defect of vision in which a person can see near oobjects clearly but cannot see distant objects clearly.
it is due to : 1) elongation of eyeball
2) excessive curvature of eye lens (low focal length)
both these causes rays to focus in front of retina.
this can be corrected by using concave lens of appropriate power.
hypermetropia : this is a defect in which a person can see distant objects clearly but cannot see nearby objects clearly. Their least distance of distinct(clear) vision is more than 25cm.
it is due to : 1) shorter eyebal
2) focal length of eye lens is too long.
in both these cases rays coming to eye will be focused behind retina by eye lens.
this can be corrected by using convex lens of appropriate power.
there is another defect also named presbyopia found in old people.
it is due to loss of flexibility of eye lens.
in this near point of distinct vision recedes away.
can be corrected by using convex lens.
