Today I'm blogging about tapetum lucidum. What is that?
|Hello cutie lemur! Source: Wikipedia|
The color of the eyeshine you see depends on the angle of the light hitting the animal's eye, and the kind of animal. Each species has its own set of different crystals that make up the tapetum lucidum, and that is why:
- Some fish have white eyeshine
- Horses have blue eyeshine
- Cats, dogs and raccoons have green eyeshine
- Rodents and birds have red eyeshine
What about humans? Well, humans and most other primates don't have a tapetum lucidum.
What about red-eye in photographs? This occurs when the camera flash is very close to the lens that is taking the photograph. The light hits the choroid (a blood vessel layer behind the retina) and reflect back into the camera, which records the photo. The red color comes from the redness of the blood
Why do some people always have red-eye in photos? Or the reverse question, why do people like me never get red-eye? People who have lighter skin tone and blue eyes often have less melanin (dark pigment) on the inner surface of their eye (the fundus, which contains the retina, optic disc, fovea and macula) so more light is able to pass through to the choroid. In people like me, the melanin in my fundus (geez, that sound SO PERSONAL) absorbs that light and very little gets reflected back by my choroid.
How did they do this in Blade Runner?
|Rachel and Deckard have a moment. (Source: Warner Bros.)|
Man, wasn't that cool??? They showed the eyeshine of an artificial owl too, and the eyeshine of both Rachel (a replicant) and the owl highlighted the fact that they were both artificial. Beautiful and perfect, but fake.
What the director did was shine a light straight at Rachel that was extremely close to the camera lens. If you look carefully, you'll see that Han Solo (whoops, I mean Indiana. *slaps face* I mean Harrison Ford!) has a faint eyeshine, but you don't notice it in the movie because Rachel closer and in focus.
What's the red reflex?
This is a reflex that doctors look for when we sometimes shine light into your eye during an exam. In kids, the reflex is very bright. When a more white reflex is observed instead (called leucocoria), that is usually a sign of pathology, like an eye cancer (retinoblastoma in kids), cataracts in older individuals, or other problems.
Well! Everything you needed to know about eyeshine! Thanks for stopping by and leave any questions in the comments. :)