A person needs a lens of power -4.5 D for correction of her vision. What kind of defect in vision is she suffering from?

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Myopia.

Ptosis.

Presbyopia

Diplopia

answer is A.

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Detailed Solution

Concept: The person has an eye disease and it is assumed that a -4.5D lens is needed to correct the vision impairment. The reciprocal of the focal length of the lens is defined as the power of the lens. Therefore, if you have a lens with a focal length of f, the refractive power of that lens is:

The SI unit of power of the lens is diopter (D) . And

. Assume that the lens power required for the subject is -4.5D. This means

Substitute the value of P into equation (i) .
Question Image

This means that the focal length of the lens should be -0.22m. Since the focal length of the lens is negative, the required lens is a negative (concave) lens. This means that the image is created in front of the retina. Therefore, humans suffer from myopia in which images of objects are formed in front of the retina rather than on the retina. Therefore, the correct option is 1.
Hence, the correct answer option (1) .

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