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A myopic person has been using spectacle...

A myopic person has been using spectacles of power -1.0 dioptre for distance vision. During old age he also needs to use separate reading glass of power +2.0 dioptres. Explain what may have happened.

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The far point of the person is 100 cm, While his point may have been normal (about 25 cm ). Objects at infinity produce virtual image at 100 cm (using spectacles ). To view closer objects i.e., those which are (or whose images using the spectacles are ) between 100 cm and 25 cm, the person uses the ability of accommodation of his eye-lens. This ability usually gets partially lost in old age (presbyopia). the near point of the person recedes to 50 cm . To view objects at 25 cm clearly. the person needs converging lens of power + 2 dioptres.
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