A person with a nearsighted eye has near and far pointsof 17 cmand 28 cm, respec

Question

A person with a nearsighted eye has near and far pointsof 17 cmand 28 cm, respectively. (a) Assuming a lens is placed 2.0 cm from the eye, what power mustthe lens have to correct this condition?
P = diopters

(b) Suppose contact lenses placed directly on the cornea are usedto correct the person's eye. What is the power of the lens requiredin this case, and what is the new nearpoint? Hint: The contact lens and the eyeglasslens require slightly different powers because they are atdifferent distances from the eye.
P = diopters
p = cm
(a) Assuming a lens is placed 2.0 cm from the eye, what power mustthe lens have to correct this condition?
P = diopters

(b) Suppose contact lenses placed directly on the cornea are usedto correct the person's eye. What is the power of the lens requiredin this case, and what is the new nearpoint? Hint: The contact lens and the eyeglasslens require slightly different powers because they are atdifferent distances from the eye.
P = diopters
p = cm

Explanation / Answer

(a)Assuming a lens is placed 2.0 cm from the eye, what power must thelens have to correct this condition?
P = diopters
in this case the far point is 28-2=26cm
now power P= -1/f=1/[26/100]= -3.846 D
(b) Suppose contact lenses placed directly on the cornea are usedto correct the person's eye. What is the power of the lens requiredin this case, and what is the new nearpoint? Hint: The contact lens and the eyeglasslens require slightly different powers because they are atdifferent distances from the eye.
P = diopters
p = cm              power= -1/f=1/[28/100]=-3.5714D
in the above two cases - ve sign indicates that he needs a concavelens

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