It's nice to think that ferrets, famous for their amusing antics, muck about solely for the entertainment of their humans. The truth is, the way their eyes work plays a big role in their 'silliness'.
Where's the floor?
Most ferrets have very bad depth perception and will walk nonchalantly off a table, bookcase, or windowsill without hesitation. Perhaps they can't see how far down the floor really is.
Though you might find this habit of theirs amusing, safety is an issue; you should ferret-proof your home so your fuzzies can't climb up tall objects and then fall off. Some ferrets are terribly afraid of heights and will scramble away from the edge of a table, or be extremely uncomfortable about riding on your shoulder unless supported by your hand.
Ferrets have 'binocular' or 'stereoscopic' vision, meaning that their eyes are placed more to the sides of their heads than human eyes are. This gives ferrets much better peripheral (side) vision. Because a ferret's eyes are one solid colour (usually black), people sometimes assume that the eyes are fixed in the head. This is of course incorrect. Like humans, ferrets can move their eyes without moving their head.
Ferrets don't see much detail beyond a few feet, so it's not likely that your ferrets see the specifics of your face when they look up at you; they just know that you have a face.
All this might make it sound as if your ferret is at a huge disadvantage as he makes his way around. But overall, ferrets depend more on their senses of smell, hearing, and touch than on their vision. Also, at close range (one or two ferret lengths), your ferret actually sees better detail than you do — and better detail than a cat does. Ferrets do have a blind spot right in front of their nose, so they'll sniff when looking at something close-up.
Seeing in the dark
Ferret eyes work best at twilight, an ability that was probably inherited from wild polecat cousins who hunted at dusk and dawn. Ferrets don't see well in pitch dark and have difficulty adapting to sudden bright light. However, they see in low-light conditions much better than humans do. This is because ferrets, like cats and horses, have something called a 'tapetum lucidum' at the back of each eye — a reflective layer that shines even the smallest amount of light back into the eye. It is also because of the tapetum that a ferret's eyes seem to glow in the dark.
Pupil shape also helps ferrets see well in low-light conditions. Unlike humans, who have round pupils, ferrets have slit pupils. This enhances edge detection and makes objects more visible in poor light. Cats, too, have slit pupils, but theirs are slit vertically, while ferrets' are slit horizontally. Because of this, a ball bouncing up and down is much more exciting for your ferret than for your cat (who would prefer to see the ball zip across the floor). The slit pupil makes up for the ferret's nearsightedness: Although ferrets can't make out distance detail, they see movement quite well. So if you stand still, your ferret may not see you across the room, but as soon as you move, he will.
Red is the only colour that domesticated ferrets can see; other colours appear as shades of grey. This is not surprising, because colour is not important for seeing in low-light conditions. So don't deliberate for too long over what colour hammock to get for your ferret.
Older ferrets lose their vision just like older humans do, and they may become totally blind toward the end of their life because of cataracts. Albino ferrets often suffer from being cross-eyed, which reduces their ability to see. Also, some albinos have an abnormality that sends scrambled signals from the eye to the brain, which disrupts binocular vision and the ability to correctly process visual stimuli. Coloured ferrets with albino genes (especially cinnamons, dark-eyed whites, and pandas)