I have looked at the causes of blindness in babies. This is what I decided on.
Ixonia was born with Retinopathy of Prematurity. Her mother fell from high wire while pregnant, jarring Ixonia out yet not all of the way. Her name is the only name she could come up with an "X" in to mark the spot where she was born at.
I have made a Real Life Vampire RP once. I still have the notes on it. But that is the only RP where I investigated known diseases and conditions were the cause of vampireism. Time to do another series!