Aestolia's eyes were injured as a result of a magic backlash while casting a Forbidden Spell, shortly after she had just promoted to an Arcane Magician.
Backlashes of magic are serious accidents. In minor cases, they result in injury, but in severe cases, they can cause a person to burst and die. Despite the price of damaging her eyes, she managed to survive.
However, this didn't seem to be a bad thing. Although she lost her sight, Aestolia's perception of the Magic Elements became keener, and her understanding of magic became more three-dimensional and vivid.
This resulted in a massive progression in her understanding of magic. She broke the boundary between the arcane and the truth, become a Truth Mage, and awakened the Forbidden Magic Domain, which is considered the nemesis of mages. She earned the title of the God of Truth and Law in the Elemental Deadland.
"Perhaps because I'm blind, I am more sensitive to the elements," was Aestolia's conclusion.