I Have Developed A Circle Of White, About The Thinness

I have developed a circle of white, about the thinness of a white string, in my right eye. It is not a floater, but it only moves when I move my eyeball. I see a retina specialist once a year and I mentioned it to him and he said it was a type of floater. It use to be a half circle, now it's almost a complete circle. I am beginning to get some distortion around it. Should I be concerned...what could it be. When I look at the computer screen it's about the size of a pea. Thanks for any info.