Red eye problems?

Question

Why are some people's eyes more susceptible to turning red in photographs then others? What actually causes that?

Answer 1

The number of rods at the back of the eye, more rods mean more reflection and worse 'red eye'.

Dogs are far worse the people, the "devil dog" effect.  I'm worse than anyone else I know for it, but that's because I have more rods and fewer cones.  (I have excellent night vision, but poor color vision.)