Sharks are not blind; this is a common misconception. They possess highly specialized eyes adapted for their underwater world, with a visual system structured to perform in low light and murky water. While eyesight is not their most dominant sense, it is a component of their sensory toolkit.
How Sharks See Underwater
A shark’s eye is similar in structure to that of other vertebrates, containing a cornea, lens, retina, and iris. Their vision is enhanced by the tapetum lucidum, a layer of reflective crystals behind the retina. This structure reflects light back through the retina, significantly increasing its sensitivity. This adaptation allows sharks to see effectively in dark or cloudy water, especially during dawn and dusk.
A shark’s retina is rich in photoreceptor cells known as rods, which are highly sensitive to light and movement. This gives them excellent vision in low-light conditions. Conversely, they have fewer cone cells, which detect color. While once believed to be colorblind, recent studies indicate some species may have cone cells, suggesting a potential for some color vision.
The placement of their eyes on the sides of their head grants them an almost 360-degree field of view. This wide perspective helps them detect prey and threats from nearly all directions. This positioning, however, creates blind spots directly in front of their snout and behind their head.
The Protective Eyelid Misconception
The misconception that sharks are blind is often fueled by a misunderstanding of their protective eye mechanisms. Many shark species possess a nictitating membrane, a translucent third eyelid that covers the eye. This membrane slides over the eyeball to shield it from debris or struggling prey during an attack.
Some species, like the great white shark, lack a nictitating membrane. To protect their eyes, they instead roll them backward into their sockets just before making contact with prey. This behavior gives them a white-eyed appearance and is a defensive reflex to prevent injury to the eyeball.
Vision in the Context of Other Senses
Vision is just one component of a shark’s sensory system. Their sense of smell is powerful, allowing them to detect minute amounts of blood in the water over vast distances. This helps them track prey from far away.
Sharks also possess a sense that allows them to detect weak electrical fields through pores around their snout called the ampullae of Lorenzini. All living animals generate a faint electrical field through muscle contractions. Sharks use these signals to locate prey hidden or buried in the sand, combining this sense with sharp hearing and their lateral line to feel water movements.