It wasn't apart of my DNA, it was the day before I met and fought for Luna against King Sombra. I was training with some of her soliders to prepare for the war and I toke down all of them but one and it was my arch enemy trying to kill me, they were wielding a sword and then they cut one of my eyes I was blind that day and I started to wear sunglasses so no pony would think of me as a freak or a disgrace it was till a few wars after Luna asked to see me for dinner as soon as it began she asked for me to remove my glasses and I asked her "Are you sure?, you might not like what you see." she nodded and said "Yes!". I removed my glasses and she saw I was blind and she asked me "what happened to you?" as I told her the story she had tears coming from her eyes and then she asked "How are you able to fight so greatly?" I tell her whilst losing 1/2 of a sense my other senses have gotten stronger. From that day I became her best friend she felt sorry that I'm blind but she knows that no matter the odds I'll be there to protect her and then she made me her army's General. But yet even with partial vision I'm a warrior and I'll die for Luna.