Question

Darcy suffers from farsightedness equally severely in both eyes. The focal length of either of Darcy's eyes is 19.0 mm in its most accommodated state (i.e, when the eye is focusing on the closest object that it can clearly see) What lens strength (a.k.a., lens power) of contact lenses should be prescribed to correct the farsightedness in Darcy's eyes? (Assume the lens-to retina distance of Darcy's eyes is 2.00 cm, and the contact lenses are placed a negligibly small distance from the front of Darcy's eyes)

Answer 1

First let's find out the near point of Darcy's eyes.

Given that in most accommodated state, fe=1.9cm and v=2cm

So, using lens formula we can write,

So the near point is 38 cm. Therefore the corrective contact lens should form the image of object at 25 cm (minimum vision distance for a healthy eye) at 38 cm from eye.

therefore, for the contact lens,

u=-25cm, v=-38 cm.

again, by using lens formula we can write,

so power of the lens is