>I've assumed ferrets' light receptors aren't just through their eyes,
>and that even blind ones need many hours of darkness. True?

The CAUSE of the blindness matters.

There IS work (in Scandinavia and probably elsewhere now) in humans
with different types of blindness on the amount that melatonin
production is affected by light exposure. The type of blindness
matters. In some types nothing gets through from the eyes in any way
and those people produce more melatonin, a tumor fighter among other
things, which also means less LH and less FSH produced since those go
up when melatonin goes down. Chronic too high levels of LH is the usual
trigger for adrenal neoplasia and chronic too much FSH can cause bone
loss. There also are blind people who still have the presence of light
registered hormonally if not visually, and in some blindness there can
be a sensation of light. Much of blindness is a continuum with multiple
types as well.

It was actually due to epidemiological work in Scandinavia noticing
that many blind people had much lower levels of hormonal malignancies
which ultimately led to finding that melatonin is a tumor fighter.

A recent study that I did not save (sorry) was on an alternate pathway
rather than sensed vision (and I think through alternate minor neural
pathways rather than use of the optic nerve, so I think in those of us
with glaucoma even when it is fully bad) in which light was registered
w hormonal results but not sensed by the people.

There also was work maybe about 2 decades ago now to see if light on
the backs of the knees changed melatonin levels for the worse. The
study I know of where that was done found no difference.

BTW, for anyone who was wondering who I forgot to tell: the surgery
trial using SLT on my worse eye instead of my usual ALT got my eye
pressure down enough for a while again, so that is in my arsenal
now, too.

Sukie (not a vet) Ferrets make the world a game.

Recommended ferret health links:
http://pets.groups.yahoo.com/group/ferrethealth/
http://ferrethealth.org/archive/
http://www.miamiferret.org/
http://www.ferrethealth.msu.edu/
http://www.ferretcongress.org/
http://www.trifl.org/index.shtml
http://homepage.mac.com/sukie/sukiesferretlinks.html
all ferret topics:
http://listserv.ferretmailinglist.org/archives/ferret-search.html

"All hail the procrastinators for they shall rule the world tomorrow."
(2010, Steve Crandall)
On change for its own sake: "You can go really fast if you just jump
off the cliff." (2010, Steve Crandall)
A nation is as free as the least within it.

[Posted in FML 7515]