The Red-Eye Effect

After finishing my last blog post relating to cats' tapetum and their ability to see in darkness I couldn't help but be reminded of another scenario where the eye reflects a bright color. On Thanksgiving my aunt insisted on taking a photo of our family with her flash camera. When we reviewed the picture the majority of us had shining red eyes. Now, it's not as if we were possessed by some demon while taking the photo; everyones' eyes react the same way when they face the camera directly. The "red-eye effect" is a reaction that happens due to flash photography. The pupils do not have time to dilate in reaction to the bright flash, so the flash's light is able to travel directly to the back of the eye where the retina is located. So, when you take a flash photo and see those red eyes, you're actually looking at a reflection of your retina! The reason the retina displays as red is due to whats called the choroid. The choroid possesses a rich blood supply and acts as a connective tissue to nourish the retina, giving it that true red color. So next time you get weirded out by your red-eye pictures, remember it's not scary, it's science!