Question

A person has a far point of 27 cm and a near point of 12 cm. Her eyeglasses are 2 cm from her eye. What power lenses must be prescribed to correct this person's vision?

Answer 1

since this eye can already focus on objects locatde at thenear point of a normal eye,no correction is needed for near

objects.To correct the distant vision , a corrective lens(located 2cm from the eye) should form virtual images of very

distant objects at 27 cm in front of the lens.thus we have q =-(27-2) = -25 cm & P------>∞

thus we have

    1/f = 1/p + 1/q

               = 0+1/-25 cm

or

   f= -25 cm

refractive power is P = 1/-0.25m

                                = - 4 diopters.