Science Buddies: "Ask an Expert"

I have found several websites explaining how red-eye in flash photography occurs.

One says that it is caused by the reflection off the retina of the rhodopsin, the pink colored photopigment in the rod photoreceptors.

Website:
http://www.cis.rit.edu/people/faculty/m ... ch8p3.html


Another says that it is from the light from the camera flash bouncing off the retina (at the back of the eye). Because the retina has lots of blood vessels, the reflection looks red.

Website:
http://science.howstuffworks.com/question51.htm


Can you tell me which gives the most accurate description of how red-eye occurs.

Thank You,
Naeh.

Very interesting. I wonder if you could design an experiment to answer that question? With a microscope, Maybe you could determine whether the reflected red light comes from capillaries or from the rhodopsin.

I really don't know the answer, but I would tend to believe the RIT faculty page. Here's some other info about reflections from animals' eyes that may influence your opinion:
http://sciam.com/askexpert_question.cfm ... 9EC588F2D7

Naeh,

The coloration may be partly from the red oxygenated blood... but I believe that the real coloring agents are the pigments found in the "macula lutea". These are orangish red pigments composed of xanthophyll, carotenoids, and lutein... the very same chemicals that make carrots orange! Honest! And now you know why you need your carrots to keep your eyes healthy.

You may find this website helpful in learning more about this topic:

http://webvision.med.utah.edu/sretina.html

The color in retroreflection found in cats and other animals is from other sources... and is brighter than the reflection in primates (humans are members of the primate family) due to the special reflective layer called the tapetum:

http://en.wikipedia.org/wiki/Tapetum_lucidum

BTW... studying the human eye and human vision system is partly how I make my living... here is a link to a magazine article about me and my work:

http://www.acumeninfo.com/eprints/6365c ... Id=erights

Good Luck!