 Number two, how rigid are you? If you're not at all flexible, this is probably not going to be healthy for you. And number three, can you have just a little bit? You've got to be able to control yourself with this diet. I'm Dr. Sanjay Gupta, helping you live a better life. While retinitis pigmentosa takes Mark's vision, his family gives him hope, whether at the family business or at home with his wife and sons. He knows he's not fighting alone.