“It remains unknown what makes certain blood mages react so differently to the disturbing practice’s effects.
The first stage—the one most common to any mage attempting to dabble in blood magic—doesn’t directly affect any physical aspects, barring the wounds inflicted on themselves while procurring the closest blood source to them (of course, non other but their own blood), and mental ones that are to be expected in this situation since no mage of sound mind would ever attempt such a fate.
The second stage, already a wildly uncommon one, is said to occur after prolonged blood magic use. The irises turn a deeply dark hue no matter the original eye color, as if all light dares not touch such sin. In the same fashion, but largely believed to be a mere tale and just that, the entire eye (sclera, iris and pupil alike) loses any sensible color and turns a lifeless black that, however, doesn’t seem to obstract sight.
Many fellow scholars have theorized that blood mages exhibiting signs of the second but, especially, third stage, are far less likely to be able to give up or even be cured of their aversive ways, if that’s even possible. Are they simply too far gone? Or is blood magic a demon of a far bigger extent we cannot even dare imagine?”
—From a letter found on a dead body by Inquisition forces, author unknown