What Causes A Mild Arch In The Penis?

I have been doing some research to try to assess the curve in my penis, I know that people say it is normal to have a curve and not straight, but I was wondering how to differentiate between a normal curve and peryione's disease. What degree would be considered a normal curve? I dont feel any scar tissue or anything like that, just notice when looking at it. Also, is it true that Vitamin E can reduce the curve?