In presbyopia,the near point of the eye gradually recedes away. Thus it is a case similar to hypermetropia. The why shouldn't we use a convex lens to correct this defect instead of a bifocal lens?

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Solution

An eye that suffers from myopia as well as from hypermetropia is said to suffer from presbyopia. A person with this defect cannot see objects distinctly placed at any distance from him.
To correct this defect, a person is prescribed bifocal lens that has both types of lenses �� convex and concave.

If convex is used only hypermetronia can be treated

If concave is used myopia is treated...

So if only convex lens are used,in a condition of both hypermetropia and myopia ,myopia is not treated

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Q. The bifocal lens used in the correction of presbyopia has a ___ lens on upper side and a convex lens on lower side.

Q. Can't we use concavo-convex or convexo-concave instead of bifocal lens for presbyopia patient?

Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.

Rewrite the following table so as to match second and third column with first column

Column		Column II	Column III
(1)	Myopia	Old age problem	Convex lens
(2)	Hypermetropia	Near-sightedness	Bifocal lens
(3)	Presbyopia	Long sightedness	Concave lens

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