Penguins have flattened corneas, which refract (bend) light less than human corneas do. In effect, it’s up to a penguin’s lens, not the animal’s cornea, to focus light onto the retina. Luckily, penguins are well-adapted to do that. They also have strong eye muscles that can change the shape of the lens when the birds are on land or in the water, according to the New England Aquarium.
What’s more, the birds have clear eyelids, called nictitating membranes, that protect their eyes when they’re swimming underwater, the aquarium said. These adaptations help penguins see wherever they go!