question_answer 25)

A myopic person has been using spectacles of power- 1.0 dioptres for distant vision. Duringold age he also needs to use separate readingglass of power +2 dioptres. Explain what may have happened.  

Answer:

For -1 -0 dioptre, the far point for eyes is 1 mi.e. 100 cm. The near point is 25 cm. Theobjects lying at infinity are brought at 100 cmfrom his eyes using the' concave lens and theobjects lying in between 25 cm and 100 cmare brought to focus using the ability ofaccommodation of the eye lens. In the old age,this ability of accommodation is reduced andthe near point reaches 50 cm from his eyes. Usingwe get. i.e. f = 50 cm and dioptre The person requires glasses of + 2 dioptre.