For persons who can only see objects clearly that lie between 25 cm and 250 cm f

Question

For persons who can only see objects clearly that lie between 25 cm and 250 cm from their eyes, what is the change in refractive power of their eyes, in diopters? (Assume a lens-to-retina distance of 2.00 cm.)

--> I got the correct answer of 3.6 diopters.

What strength of contact lenses should be prescribed to correct this myopia (answer in diopters)?

--> I've tried -3.6, -3.5, -4.0 i'm not quite sure what to put here or how to find the correct answer as these were all wrong.

If they read a book while wearing contact lenses, what is the minimum distance from their eyes at which they can focus on the book?

--> I've tried this as well but my answer was wrong

Explanation / Answer

for myopia,

P = 1/2.5 + 1/inf

= -0.4 + 0

= -0.4 D

4 - 0.4 = 1/d +1/inf

d = 27.8 cm

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