Question

. Now assuming Anna's far point was found to be 0.9 m (i.e., her eyes can't focus on any object more than 0.9 m away), what power corrective lenses would you prescribe to Hannah so that, when wearing these lenses, her visual range was the same as Anna's (from a near point of 20 cm to a far point of infinity? Give your answer in units of diopters, to the nearest tenth of a diopter, with the correct sign.
5. One treatment of cataracts is to surgically remove the variable lens of the eye. If we assume that the cornea's refractive power focuses objects at infinite distances onto the retina of a person who has had this surgery, what power correcting lenses would they need to be able to read text at a 21-cm near-point distance? Again, give your answer in units of diopters, to the nearest tenth of a diopter and with the correct sign.

Answer 1

Answer:1). Distance of far point x=0.9m

Therefore, since the image is virtual

-f=-x = -0.9m

Power of the concave lenses = 1/f = 1/-0.9

= -1.11D

2 ) near point is 21cm = 0.21m

Power = 4-1/near point

= 4/0.21

= 14.2D.