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Shortsightedness is due to reduced focal length and long sightedness is due to increased focal length.howcan the focal length of eye lens change overtime?

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The lens becomes stiffer as people age and people can't focus on objects close to the eye. We focus our vision using muscles that pull on fibers to change the shape of the lens. When the lens stiffens, it doesn't allow for good focusing of near objects.

https://www.mayoclinic.org/diseases-conditions/presbyopia/symptoms-causes/syc-20363328#:~:text=Presbyopia%20is%20caused%20by%20a,images%20appear%20out%20of%20focus.

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Things like this are because of the curvature of the lens of your eye. If it’s too curved the focal point of your eye will land somewhere in front of your retina causing myopia, or short-sightedness, and in the case of your lens being not curved enough, the focal point lands behind the retina and you have hyperopia or long sightedness.

How this happens over time (or if you are born with it) is a medical question and perhaps should be answered on one of the medical stack exchange sites.

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  • $\begingroup$ I think you got "behind" / "in front of the retina" wrong. Otherwise a good answer. $\endgroup$ Nov 19, 2020 at 10:51
  • $\begingroup$ @RalfKleberhoff You're right. Thanks Ralf. $\endgroup$
    – joseph h
    Nov 19, 2020 at 21:04
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You are going wrong

Shortsightedness is due to reduced focal length

Rather you wear

reduced focal length

or concave lens due to Short sightedness So if your eye sight improves then the focal length of lens decreases but it has no relation that change focal length will change your eye problem.

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  • $\begingroup$ OP is not talking about glasses, but rather the focal length of the eye lens $\endgroup$ Nov 19, 2020 at 9:07
  • $\begingroup$ then he should clearly mention human eye lens $\endgroup$
    – Ha'Penny
    Nov 19, 2020 at 10:39

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