Why does myopia develop from prolonged near work?

[Puneeth423]

Will a person suffering from nearsightedness, couldn't see objects far since his eyeball is longer than the usual? (or) Because when he reads more books daily and always focus his vision on objects nearer, lens in his eye ball becomes stub burn and doesn't adjust its focal length when he watches objects far away?

 

[Drakkith]

I think just the latter. If your eyeball changes length it should affect the focus of all of your vision, not just the far away focus.

 

[sophiecentaur]

The Physics / optics is that objects at only one distance are focussed on the retina. You adjust the focal length of your lens in order to accommodate over your range and get a particular object in focus. If your eye is 'longer' than normal, even with the lens muscles totally relaxed, distant objects are still not in focus (myopia). If your eye is too short (or you are old and the muscles won't work hard enough), then the muscles cannot change the focal length of the lens to bring near objects into focus.
As far as I know, it is not possible to deal with myopia by 'exercising' the muscles because they are already relaxed when you are trying to see distant objects. Some people claim that exercising the eye muscles can help with hypermetropia though.
My eyeball is aymmetrical and I suffer from astigmatism. The only way to deal with that is with glasses that have a cylindrical element to the lens shapes. So I can just be lazy.