The eyes are the most sensitive and smallest sensory organ in the body of a living organism. However, it is also the most complex and intriguing sensory organ. The functioning of human eyes resembles that of a camera. Cornea, the transparent frontal part of the eye helps in protecting the iris, the pupil, and the anterior chambers. It also provides the eye with the majority of its optical power. However, we are only able to see things once the light enters the pupil. The pupil functions as the shutter of a camera. It also controls the extent of light, entering our eyes. Then after, the light gets focused on a thin sensory membrane called the retina. Over the retina, the image of the object is formed. Further, the brain receives the signal through the optic nerves. Thus, the image is interpreted and we are able to see what’s in front of our eyes.
However, the structural composition of some animal’s eye is slightly different from the eye structure of a human. This is one major cause of the fact that the eyes of animals glow in the dark.
Have you ever been scared of your dog in the dark? Or have you come across the illuminating eyes of an owl in the night sky? If yes, then we are sure that it must have been a scary experience. Nonetheless, there is nothing supernatural about this phenomenon of glowing eyes of animals. It can be explained scientifically.
Doctors call this phenomenon ‘Eyeshine’ or ‘Retroreflection’. The eyes of animals consist of an extra reflective layer of tissue. It is called the Tapetum Lucidum. The name sounds like a spell from the books of Harry Potter, right? Nevertheless, it is just a simple mirror like tissue and it is also referred to as the Bright-Carpet. The Tapetum Lucidum is placed underneath the Retina of the eye of the animal. The function of the Tapetum Lucidum is to reflect back the visible lights entering the eyes of the animal, through the retina. It implies that the light rays which enter into the eye get reflected back at the object from which it was first emitted. This way, it allows the eyes of the animals to absorb the maximum amount of light as it is reflected by and through the retina. Thus, it helps in enhancing the extent of availability of light to photoreceptor cells. Although, it blurs the image they visualize it helps the animals to have a better night vision than humans and some other animals. Furthermore, the amount of light which doesn’t get absorbed is routed in the opposite direction. Therefore, the eyes of animals such as dogs, cats, bats, tigers, etc. seem to be shining in the dark.
On the contrary, the human eye does not possess this special layer of tissue called the Tapetum Lucidum. This is the reason why the ability of the eyes of animals to see in the dark is superior to that of humans.