Well, yes and no. Many factors affect visual acuity including the shape of the eyeball (affects focal point of lens on retina), cornea (defects cause astigmatism), retinal damage like macular degeneration which leads to functional blindness, and the function of the muscles which adjust our focus within our visual range. Eye strain can take a significant toll on those muscles and eventually lead to a sometimes significant loss of visual acuity (myopia.) Fortunately the muscles can often be retrained. Search Amazon for books on vision correction and you will find a ton of books that essentially help you retrain your eye muscles to improve your visual acuity.

sample book on Amazon http://www.amazon.com/Relearning-See-Improve-Eyesight-Natura...