Have you ever opened your eyes underwater?
Its not that you can’t see, but certainly that you can’t see CLEARLY. And definitely not clearly enough to hunt. How do sea lions and other marine mammals do it?
Well, it’s definitely multiple factors. Firstly, their eyes are proportionally larger than our eyes, so they are able to absorb more light underwater. They also have increased light sensitivity, which is traded for color sensitivity. Its believed that they can see colors on the blue and green spectrum, but with increased light sensitivity they can get more light underwater.
Secondly, they have a transparent THIRD eyelid! Here’s your word for the day: nictitating membrane. Many animals have this third transparent eye lid when they live in diverse or adverse conditions. Camels have this to protect their eyes from sand, and many marine mammals have it to protect and see underwater. Except in the case of sea lions, their natural eye is what they use underwater: they use their nictitating membrane on land to protect from sun and sand.
Unlike the upper and lower eye lids you have, these eyelids move horizontally across the eye.
Thirdly, their eyes are set in a cushion of fat, which offers a pillow for the eyes when our favorite “ocean dogs” dive and the pressure becomes great.
We have found ways to adapt to their underwater world, but sea lions and seals are naturally set! Amazing! Perhaps we should take a note from them in future scuba diving gear innovation.
Other animals with nictitating membrane:
Polar bears (to protect from snow blindness)
Sharks (protection from prey who object to being eaten)
Beavers: to protect WHILE diving
Eagles: to protect their eyes while feeding chicks
Cats (and dogs) because cats are the boss of you and can do whatever the hell they want, include have third eyelids.