As you get older, a few things happen. First, as your eyes lose the ability to focus (which is a gradual process, not a step change), you find that over time y

As you get older, a few things happen. First, as your eyes lose the ability to focus (which is a gradual process, not a step change), you find that over time you need more and more lenses: one for objects at 18 inches (your laptop), one for objects at 24 inches (your monitor), etc. You don't always have the proper lenses at hand when you need them. Second, all the transparent bits of the eyes slowly become less transparent with time. Some problems (cataracts for instance) can be fixed with surgery; others would require replacing the entire eyeball. Third, a number of unlucky people develop problems with their retinas, which may or may not be fixable, and the fixes rarely leave the retina in as good a shape as it was when it was younger. So "wear corrective lenses" is not a bad suggestion, but if web designers are targeting older people, they need to assume the the reader's eyes are not what they once were, and that there may not be much that the reader can do about it.