Jep, blame it on the spellweavers. *chuckle* I thought of that too, but the topic went already in the medical direction and I once needed those infos to answer a similar question to create a temporary eye injury for a charakter of mine.
I think a permanent effekt would only occur if your char suffers from Coagulopathy, a condition in which the blood’s ability to clot is impaired. But even then I'm not sure, the eye would stay red permanently, if it even could happen only to a local area or if it is a condition your whole boody suffers. (Haemophilia sure…