May I ask how old your son is?
Here's the thing - cats will often bond to a single human,
and your cat may have already bonded. There are some things
you can do to correct that, maybe -- but since your cat is
blind, I'm concerned that your son is really responsible enough
to take on the duty. Caring for an animal, as you know, takes
work. Caring for a disabled animal takes just that bit more.
Are you the source of food? Are you the source of care? Are you
a calm presence? Is your son young enough that he is too boistrous
with the cat? Does he have the patience to let the cat come to him,
If you son is old enough/responsible enough, and you really want
the cat to be his, then he has to be the source of all good things --
all food, water, litterbox hygiene, calm laps, etc. If your son has
a hectic schedule and won't be home much, this may be very
difficult for him to accomplish! Especially since cats respond
best to routine!
It is not uncommon that a child's pet is actually the parent's pet,
because the parent is the true, although shadow, caretaker.
You and your son should have a serious, heart-to-heart about
this -- for the cat's sake!
I hope this does not sound judgemental - for all I know, your son is
an adult! I'm just trying to help, here. :-)