The average eyeball is about 2.4cm in diameter, but certain people can have shortened eyeballs and this is known as Hyperopia. And an elongated eyeball is Myopia. Both affect the afflicted with blurry vision. A sufferer of Hyperopia has what's called a near point that is farther away than 25cm, but has a normal far point which is "infinitely far away". This means that anything within the sufferer's near point is blurry and a sufferer is called farsighted. A sufferer of Myopia has a normal near point, but the far point is not normal because the sufferer can only see clearly within a certain range of let's say 200cm when the individual really needs to see "infinitely far away." This means that the sufferer can't see anything clearly far away and is considered nearsighted.
To correct these anomalies, a sufferer is prescribed eyeglasses or contact lenses. When I was working on a homework assignment yesterday, I came across a problem that said a person can have both problems and their vision can be corrected using something called bifocals.
If we look at this equation
1/f = 1/**i + 1/d_o
f = focal length, but an optometrist is more interested in knowing the diopter which is 1/f.
d_i = image distance
d_o = object distance
A normal eye should have something that looks like this
1/f = 1/.25 + 1/(infinity)
This is set up to find the diopter for a nearsighted person because we want to be able to see infinitely far away, but the vision is limited to 200cm.
1/f = 1/(-2) + 1/(infinity)
This is the set up to find the diopter for a farsighted person because we want to have a near point that is 25cm, but the real near point is much farther away like 40cm.
1/f = 1/.25 - 1/.40
Ah I probably lost some of you lol. But at least I have to try, and maybe someone understood parts of it. Note to myself, never be a teacher lol.
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15-Jun-2015 00:24:01