Why do animal’s eyes glow in the dark?

         In animals belonging to the cat family and other nocturnal animals the back of the eye ball – the retina, has a layer called “tapetum lucidum”. This layer is made of special cells which reflect light falling on the retina. It is this layer which makes the eyes of these animals glow in the dark. The tapetum layer also helps the animals in gathering all the available light to see in near darkness