Or short sighted folks - I have -6 in both eyes and at 10cm things do look awfully sharp. Though more than 10cm away (without glasses/contacts) things are rather fuzzy.
As another nearsighted individual (-4ish), I can attest to this. At short range, without glasses or contacts, I have ridiculous vision, much tighter and sharper than when I have my contacts in, again at very close range. Long range is much less impressive.
Short sightedness is a convergence problem. There's nothing wrong with your fovea, so you still have the sharp vision when using glasses or looking close.