Assume you have perfect eyesight, meaning that you can focus on objects ranging

Question

Assume you have perfect eyesight, meaning that you can focus on objects ranging from 25cm in front of your eye (typical reading distance) up to infinite distances. If the diameter of your eyeball (i.e. the distance between the lens and the retina) is 2.439cm, then (a) what is the focal length f and focal power P of the eye in the near-accommodated state? (b) what is the focal length f and focal power P of the eye in the far-accommodated state? (c) what is the range of accommodation of your eye in diopters?

Explanation / Answer

a)
do = +25 cm
di = 2.439 cm
use:
1/f = 1/do + 1/di
= 1/25 + 1/2.439
f = 2.22 cm

P= 100 / f in cm
= 100/2.22
= 45 D

b)
do = inf
di = 2.439 cm
use:
1/f = 1/do + 1/di
= 1/inf + 1/2.439
f = 2.439 cm

P= 100 / f in cm
= 100/2.439
= 41 D

c)
range is 41 D to 45 D

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