My eldest, Pepper, was born on Easter Sunday 1997 and died October 31st 2003, he was from a breeder and had NO health problems at all (well, I don't really know how he died but he didn't have any lumps, bumps, respiratory problems), so considering your one is around 6 yrs old, blind and has an abscess, he's a little fighter!

My little male rat has had abscesses, one that we had "popped" at the vet and one that popped by itself here. DO NOT attempt to pop it yourself! What you can do for him is bathe him in warm, salt water (just a few pinches of salt, not too much!) the water should be warm enough, (like you would wash your hands in) so that it doesn't sting or scold him. Keep him in there for about 5/10 minutes just washing over the area, don't press on it but just to keep it clean. If he doesn't agree to the bath (trust me, a guinea-pig is easier to bath than a rat ) then you can use cotton wool which is very soft and won't scratch.

Do that about 2/3 times a week and if you want to, you could take him to the vet to have it checked out.

Like the other poster asked, where is he kept? Because outside he could also catch it on something in his hutch, plus the rabbit could "groom" him and make it pop. I have no problem with rabbits and guinea-pigs being housed together provided they do get on and are well behaved with each other, but because your little one has this abscess, I would get it cleared up and out the way, or just keep a really close eye on it, checking every day, because you just never know.

Good luck, all the same!