answer:I can’t fully answer the question, but I know that the retina reflects red, which explains the red-eye effect in photos taken with the subject facing the lens and light source. Other animals (esp. nocturnal ones) have a much more reflective tapetum lucidem layer behind the retina, which enhances “eyeshine.” From most angles (i.e., off-axis) the pupil appears black, indicating that most of the light falling on it is absorbed.