A myopic adult has a far point at 0.1 m. His power of accommodation is 4 D.
(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.)

Hint: The image formed by the lens acts as an object for the eye-lens.

Step 1: Find the power of the glasses.

(i) For the myopic person,

Object distance, u=-0.1 m

Image distance, v=+0.02 m

The power, Pf=1f=1v-1u=10.02+10.1=60 D
By the corrective lens, the object distance at the far point is .
The required power is,
                            P'f=1f'=1+10.02=50 D
The power of the glasses,
Pg=50 D-60D=-10 D

Step 2: Find the near-point without glasses.

(ii) His power of accommodation is 4 D for the normal eye. Let the power of the normal eye for near vision be Pn.
Then,                          4=Pn-Pf  or  Pn=64 D
Let his near point be xn, then,
                                           1xn+10.02=64   or  1xn+50=64
                                           xn=114  
                                        xn=114=0.07 m
Step 2: Find the near-point with glasses.
(iii) With glasses P'n=P'f+4=54
                                             54=1x'n+10.02=1x'n+50
1x'n=4

                                        x'n=14= 0.25 m