a certain nearsighted eye has its vision corrected with a le

a certain nearsighted eye has its vision corrected with a lens of power -6 diopters. what is the farpoint for this eye when the contact lens is not used?

Solution

focal length of the lens

f=1/P =-1/6 =-0.1667m

for nearsighted eye d_o =infinity

from thick lens formula

1/f = 1/d_i + 1/d_o

-1/0.1667=1/d_i+1/infinity

d_i=-0.1667 m or -16.67 cm