I have become nearsighted after too much reading/computer staring. And obviously it is because my eyes are spending most time focused at <=80cm distance. Now my physics teacher said when in optics that nearsightedness was caused by the lens being permacurved, so that it could not flex back to it's flat configuration due to being held curved for so long. Somewhat like a spring that has lost it's ability to flex back due to some chemistry reasons. This is fully logical, nothing wrong with that but then I read another explaination online; Nearsightedness is caused by the muscles being locked in place, so that they cannot "relax" to let the lens is restricted in a flexed state by the eye muscles. But if the muscles were to relax the lens would automatically go to it's normal state and you would focus on the distance. Now my question is, which of the following is correct: i) nearsightedness is caused by the lens having lost it's elasticity and ability to flex to a long distance focus point when no force acts upon it. ii) Nearsightedness is caused by the focus muscles that act on the lens being permanently locked and unable to relax to allow the lens to relax itself. iii) Nearsightedness is or can be caused by ii), i) or both ii) and i) at the same time. I excuse my lack of biological terms, STEM guy here.