What Causes the Red Eye Effect?



Have you ever wondered why your eyes sometimes resemble those of a spooky vampire in photographs? Your modified appearance is caused by the red-eye effect, which occurs most often with flash photography in dark environments. This pesky phenomenon is actually a result of the eye’s biology interacting with the camera’s lighting mechanism. The eye regulates the amount of light entering the eye by contracting or expanding the pupil. At night, your pupils will accordingly enlarge to extract more light from their surroundings. However, this dilation also leaves your eyes unprepared for the sudden burst of light from a camera flash. When light from the flash enters your eyes under these conditions, your pupils are unable to contract fast enough to prevent the light from reflecting off of the red blood vessels of the choroid, which is a layer of connective tissue in the back of the eye. As a result, the camera will pick up the reflection, resulting in the red-eye effect.