Doctor Quark

[CW FOR MINOR EYE HORROR]

Doctor Quark has always been a person of science. Mad science. And one faithful evening, she discovered something that would change her life forever. Something she likes to call 'the truth'. A thing so abstract, it is unconceivable by the human eye. 

It caused her to gouge her own eyes out, and she now has light-construct eyes as a replacement. She wants to show the 'truth' to as many people as possible, no matter how gruesome the results may be. I think you can pretty clearly see how she came to become a yellow lantern.