Why does my cat always have disgusting slime bits at the side of his eyes?

My 16 year old cat called puss, always seems to have mucus like bits on the side of his eyes. It is like when you get sleep when you are younger. The only difference is it is wet and slimey just like mucus from your nose. I keep having to wipe it off. Because when i hug him it gets onto my face. Any ideas what it is?