Sharks have some of the most amazingly acute senses in the animal kingdom. They’ve adapted to be able to sense even the smallest currents or vibrations in water, and for years scientists believed that these traits had developed to make up for their poor set of peepers.
However, in the 1960s experiments were performed which proved quite the opposite; the structure of a shark’s eye is very similar to that of humans, containing both rod cells and cone cells as well as a cornea, retina, lens, the pupil and the iris. A consequence of this is that they have eyesight not just similar top our eyesight…but even better than ours and in fact a shark’s eyesight is capable of spotting a glow that is 10 times dimmer than anything we as humans can see.
The main difference between our eyesight and theirs is that sharks have a layer of tissue behind the retina called the tapetum lucidum, which allows a greta deal of light detection and greater sensitivity in the eye – an adaption which allows sharks to be adept at seeing in dark and murky water. You’d be forgiven for thinking that their eyesight is only effective underwater, but in actual fact they can see exceptionally well outside of water too… so for our sakes it’s lucky they can’t run on land!
One of the most amazing things about their eyes is the way that they protect themselves. Sharks, unlike most fish, have eyelids but they don’t have any need to blink. This is because the water in which they live cleans their eyes constantly. Many species of shark have nictitating membranes; a membrane which covers the eyes whilst hunting or being attacked. Others such as the Great White do not have this, and instead roll their eyes backwards in their head when striking prey.
Another interesting fact about the eyes of a shark is that their size and function can vary greatly depending on species. Studies have discovered that eye and pupil size differ depending on where the species of shark is found; those living only 200m below the water, for example, have larger than average eyes presumably because most light is available at shallow depths. By contrast, sharks living 4000m deep under the ocean have small eyes with large pupils to increase their visual acuity.
These adaptations are present due to primary feeding habits too – sharks which feed on faster moving prey tend to have larger eyes than those who feed on slow moving animals.
So there we have it – the myth really is just that; a myth. Sharks have an amazing set of senses which make them the viciously effective hunters they are, and though there is debate over how important eyesight is in their hunting, you certainly wouldn’t want to play hide and seek with one!
Robin blogs for leading online eyewear retailer Direct Sight.
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