My
Night Vision
By Christopher Widuch
“
! What big eyes you have, Grandma!” These were the famous words of Little Red Riding Hood when she stumbled upon a wolf in her grandmother’ s home. She likely didn’ t give a moment’ s thought to the importance of big eyes to the wolf’ s survival. Little Red quickly became more concerned with escape than understanding how some animals thrive at night while others struggle.
As human beings, we typically retreat into our homes as the sun sets and darkness prevails. It is a chance for us to wind down, to relax and reflect on the day’ s events and the next day’ s anticipations. Animals view the advent of night from a different perspective. Many work the night shift, nocturnal in nature and welcoming of the dark. They prowl, hunt, mate, even play in the dark. They are designed to thrive at night, unlike people who are considered diurnal, a term derived from the Latin diurnus meaning“ of the day” or daily.
What is it that sets nocturnal animals apart from those who hunker down at night? Clearly, the eyes hold the key. There are a number of features that allow certain animals to see at night better than others. Three of the most important traits are large eyes, an abundance of rods versus cones, and a membrane called the tapetum lucidum.
For night vision, the larger the eyes the better. Simply put, big eyes capture more light. Owls have eyes that take up about half the volume of their skulls. They are also blessed with a large lens that is located very close to the back of the eye, next to the retina. This large lens allows the retina to capture more light than other animals. There is one drawback, however, to the large amount of space their eyeballs consume. Their eyes are so big the owl can’ t actually move them; instead, they rotate their heads 270 degrees when they want to see what is to their sides.
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