I'm glad to see that the discussion has come round to the essentials: the
focused eye is a retroreflector because of the reversibility of optical
paths. We had this discussion years ago, starting from the 'pink eye'
phenomenon that arises with photographs taken with on-camera flash - I
wanted to know then why cats and dogs produce blue-eye or green-eye effects
under the same conditions, and the answer turned out to be in the
pigmentation of the reflecting layer. I had a picture of a freak cat that
had one green shining eye and one blue!
Mark
Mark Sylvester
United World College of the Adriatic
Duino TS Italy
+39 040 3739 255