How can you tell whether someone is short or long sighted? Look into their eyes.. Short sighted peoples eyes look smaller behind their glasses. Long sighted people appear to have larger eyes than normal… If you watch a film and the star of it is wearing glasses you can tell if they need them. Sometimes they wear glasses with a flat piece of glass in them, you can see a ‘flat’ reflection if the light hits them. You can tell they are only wearing glasses for effect rather than any real need.