Camera flash red-eye. Human eye photographed using a camera flash. This leads to the 'red eye' effect where the light from the camera flash reflects from a blood-rich layer in the eye. This layer is called the choroid, and it lies just behind the retina. This red glow is seen through the pupil, the normally black area at the centre of the eye where light passes into the eye. The other visible parts of the eye are the iris (brown) and the sclera (white).