[Lawtan]

(Actually one person did something like that - but simplified it to being a "progressive corrupt limb" thing.)
It could be either "Limb came back partially decayed" or "person used up part of their potential life force" - older...
Or, the spirit corroded the unused pathways from the blind eyes to the brain, making Dante's blindness irreversible...
I would say it would be an effect of alcoholism or something...

*Note: not countering Galla's comment

*The Necromancer was a Frankenstein-like fellow who wound up in a conspiracy with a magical necromancer, was stalked by witch hunters, and became a "body-snatching" spirit in order to survive...