It's not even the right eye color to be Rinoa. Her eyes are a very dark brown. Edea is the one with the goldish green eyes. And, quite clearly, that is her pupil, and is likely just a part of the same sort of distortion to her face that makes her look a little less human (which you can also see running along the bottom of the pic, beneath her eyes). It was part of the character design, either just to make her look cool, or to physically symbolize the evil and corruption.