Human eyes are in the front of our heads, giving us
depth perception and binocularity, but only about a 180-degree field of view,
while a shark’s eyes are almost on completely different sides of its head, so
the shark has a nearly 360-degree field of vision. Humans have one blind spot
in each eye; a shark has two major blind spots, which are right in front of the
snout and right behind the head.

 Sharks
can only see about 50 feet (15 meters) ahead, the sense of sight is really only
important to a shark once it has closed in on its prey.

Human
and shark eyes have many parts in common; we both have a lens, a retina, an
iris, a cornea, and a functioning pupil.

One
very important different feature of shark sight is the tapetum lucidum, which
is how sharks are able to see in the low light created by murky or deep waters­.
The tapetum lucidum, located behind the retina, is made up of mirrored
crystals. When light goes through the retina and hits the crystals, it’s
reflected back onto the retina. Cats have this same feature, and that’s why
both cat eyes and shark eyes appear to glow in the dark. In a shark, though,
the tapetum lucidum is about two times as effective at reflecting light as it
is in cats, and a shark can see about 10 times better than a human in dim light.

The
jury is still out on how a shark perceives color, for many years it was thought
that sharks only had rods, but recent discoveries are leading scientists to
believe they have cones, therefore some form of color perception.

An
unusual thing about shark eyes is the eyelid. Sharks use their eyelids
primarily as a protective measure. When it’s feeding time, or when the shark
has an encounter with another shark, it will close the eyelids to protect the
eyes from abrasion. However, a shark’s eyelids don’t close all the way. Some
sharks have a third lid known as a nictitating membrane, which will fully
protect the eye. Sharks that don’t have this feature, such as the great white
and the whale shark, roll their entire eyes into the back of their head, giving
them a white-eyed look, much like a human teenager.