After years of staring at screens at work, an optometrist told me I was shortsighted for life and insisted I buy prescription glasses. I then became a landscape gardener for four years. Guess what? My shortsightedness disappeared, as did my hayfever and weak knees. Now I am back in an office (much much better wages) and my shortsightedness is starting to return. So a combination of aggressive diagnosis and lack of eye exercise.