During embryonic development, neural tissue grows out from the brain to form the retina. In addition to a layer of photoreceptor cells, the retina includes other cells arranged in layers that process visual information from the photoreceptors (see Figure 45.20). Light must pass through all the layers of retinal cells before being captured by photosensors. In humans and other day-active animals, the light that is not captured is absorbed by a black-pigmented epithelial tissue layer behind the retina. In contrast, nocturnal animals such as deer and raccoons have an iridescent reflective layer behind their retinas, which maximizes the capture of photons by reflecting them back onto the photoreceptors. This is why a deer in the headlights or your pet dog or cat in a flash photo appears to have bright white eyes. In contrast, humans do not have a white reflective layer in the retina, so flash photographs often have a “red-eye effect,” caused by the flash being reflected by the abundant blood vessels in the retina.