Pam.
I should think that the main objection to re using old compost is the build
up of pests etc in the compost.
If you don't have to vast a quantity then you could sterilize it in your
microwave, you would be surprised how much you could do doing say 3 lots of
say 2 litres a day ( a Pyrex casserole dish with lid works great) over 2
weeks.
Mix this with fresh compost and use as normal, but I would use for different
plants to the year before if possible.
I often re use the compost from seed trays into potting mix, and it is
surprising how many slow germinating seeds will show up after a year or even
2.
Sorry to hear about the sight, what is the condition if I may ask?

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk