I just pulled a tick off one of our dogs--not on the eyelid, but it was about 2mm x 4 mm in size. Made me think of your dog, Gergraves... How long has your dog had the tag? It isn't a tick, is it?
(Although, that would be a self-resolving problem in the end as it would eventually fall off.)
I know, I know--a long shot, but I thought I'd put it out there!