I think her sight goes in and out from completely blind to able to see a bit
of shadowy movement.  The vet said it's not detached retinas, not cataracts,
and the all the blood vessels in her eyes look fine.  Her blood work is good
even for a cat half her age, and her blood pressure is normal.  She's in
great health and seems to be happy and active.  The vet guesses that it
might be a tumor on the underside of the front of her brain.  I'm not going
to have any more stressful tests done (and certainly not exploratory
surgery) since she's feeling fine, is eating well, and can get around just
fine (with just a time or two walking into a door frame when she misjudges
the route).  I've set up a carpeted ramp to my bed, and she has easy access
to food, water, and litter boxes.  She has missed the litter box a couple of
times, but I think that's Sammy's fault (Sammy is so big she can't stand
inside the box and dig at the same time so she stands on the outside of the
box and tends to throw litter all over the garage floor) - I think when
bandit feels a pile of litter under her feet she'll stop and pee even if
she's not in the box.  However, since the litter boxes are in the garage
next to the door, I can easily just hose down the floor when this happens,
so not to worry!

And yes, she can still nail an adversary with uncanny certainty when the
mood strikes her (but she is and always has been surprisingly gentle with
Sammy).