question_answer 62)

  A myopic adult has a far point at 0-1 m. His power of accomodation is 4 diopters, (i) What power lenses are required to see distant objects? (ii) What is his near point without glasses? (iii) What is his near point with glasses? (Take the image distance from the lens of the eye to the retina to be 2 cm.)       

Answer:

                  (i) Distance of far point, u = - 01 m, distance of image,  = 2 cm = 0-02 m.  Power of myopic eye,   With the corrective lens, far point shifts to . Power required, Required power of glasses, P = Pr - Pr = 50 - 60 = - 10 D. (ii)  Power of accommodation = 4 D If Pn is power of normal eye for near vision, then   or . If , is near point without glasses, then or                     (iii) With glasses,                                                                                             m