I'm away from home, but Elizabeth clipped this for me to answer, with the
words, "Isn't it your goal to bore people to death.  Just do it so I can
have some relief." Bore people?  Me?  Hummph.
 
>How do ferrets' eyes work?  Do they have pupils and iris like us (I
>understand ours to some degree)  that I just can't see?  Do they move
>independently of the head or does the ferret move it's whole head?  How
>do they focus?  My brother and I have been wondering for awhile now, and
>we haven't been able to figure it out through observation.
 
The eyes do look like little black beads, don't they?
 
They are like all mammalian eyes in that they have a retina, lens, iris,
etc.  Their pupil is round (like ours) and they can turn their eyes
independently of their head much like we do, albeit with less range
(Besides, most people will turn their heads to look at something instead of
cranking their eyes around.  That is, unless you're scoping out the fox/hunk
next to you).  There are some significant differences, however, in the
overall shape of the eye, the ability of the eye to focus, and of course, in
the structure of the retina.  Because ferrets are predators, the eyes mostly
point forward (right down the nose), but because they are also prey from
larger predators, the eyes bulge somewhat (for a wider view, like a
wide-angle lens) and are somewhat centered to the side and top of the head
when compared to large predators or humans (again, for a wider view).  So
the ferret basically looks forward to see stuff, but they have a wider view
of their surroundings than we do.  Cool, eh?
 
The vast majority of ferret's eyes are either red (in albinos) or black.
There are some ferrets with various other colors, but most owners just hear
about them, or only notice them when the light is right.  The red eyes are
red because the eye completely lacks pigments, and the color comes from the
blood circulating in the vessels of the retina.  Most other ferrets have
eyes so dark you can't see the pupil unless you look from the side while
shining a penlight into their eye.  *Then* you can see the pupil without a
problem.  Ferret eyes also have the white part (sclera), but it is behind
the eyelids and is not normally seen.  If you lift the eyelid (be very
careful) you can see some of it in the corners of the eye.
 
The retina is different from human retinas in that it has very few cones
(cones see colors) and a high density of rods (rods see tones of grey).
Also, they have a reflecting layer behind the retina that bounces light
forward, which is why ferret eyes seem to glow in the dark (biologists
looking for black-footed ferrets wait until it is dark, then shine lights
and look for green spots.  Yep, BBFs....well when they can find them).
 
Finally, the lens is structured so that the ferret can see *very* well up
close, but like the stereotypic bookworm, can't see clearly across the room.
That is not to say it can't see anything; ferrets are actually better than
people in noticing movement or shadow, they just can't read the fine print
until they get closer to see if the box says raisins or prunes, that's all.
But they don't need to, because they are specially adapted to hunt animals
that live in burrows, which are dark places without much visual distance.
So their eyes are perfectly suited for their job; that is, hunting rodents
in dark burrows.
 
And that is why the eyes are so dark.  Basic light physics says light
colored things reflect light and dark colored things absorb light, which I
learned at about three when I would walk barefoot across parking lots.  I
would race across the asphalt yelling bloody murder, then stand on the white
painted lines until the fire went out.  I crossed parking lots from line to
painted line.  The reason the asphalt was so hot compared to the white
stripe is because dark things absorb light.  Same with eyes.  You want to
see well in the dark, you need dark eyes.  Now, cats get away with light
eyes because their eyes are so big and their pupil is constructed in such a
way to allow it to open quite large compared to round pupils, but ferrets
run around underground, and thus have tiny eyes (helps keep the dirt out,
helps keep facial injuries to a minimun from fighting rats, and don't have
much use for them in the dark anyway).  So the eyes have to be dark to do
their job.  They only see in tones of gray because rods are far more
sensitive to light than cones (they can actually see a little red).  The
reflecting part of the retina bounces light forward so the same light photon
can stimulate the same rod twice, giving it a double stimuli and increasing
its ability to see in the dark tremendously.  And they see best up close
because they don't have to see the rat from across the street--just down the
tunnel a few feet.
 
Now, while the ferret's eye is basically the same as ours, they are not
nearly so dependent on vision as we are.  Instead, they use their nose to
find their way from place to place.  Foster, my 12-year-old, has recently
lost 90% or more of his sight.  I'm not sure of what he can see anymore, but
it dosn't matter much because he gets along just fine using his nose.  I
have noticed he never walks in a straight line anymore, but sort of zigzags,
using his nose as a homing device.  He startles if you grab him, but I just
call his name and let him sniff my hand first and he is fine.  Even blind,
he can still beat Carbone to the raisins.
 
Bob C and 20 MO Ferrito Banditos
[Posted in FML issue 2164]