Sight

February 4, 2025

In many shark species, the eyes are well developed, complex structures containing rod and in some species cone photoreceptor cells, that are highly sensitive to light intensity. Sharks control the amount of light entering the eye by dilating or contracting their pupils. Focusing is controlled by the rectus muscles, these pull the lens closer to or further away from the retina, when used in conjunction with the oblique muscles movement of the entire eye is achieved.

Many sharks possess excellent vision in low light conditions; this is due to the retina containing millions of rod cells together with a structure called the tapetum lucidum, this is a layer found behind the retina which reduces internal glare and scattering of light. Sharks possess an upper and lower eyelid, but these usually do not meet and therefore do not provide a full cover for the eye. Some sharks such as the tiger shark have a “third eyelid” known as the nictitating membrane, this rolls up from the base of the eye to completely cover the eyeball affording it some protection.

Species like the great white shark which do not have the nictitating membrane often employ a different strategy to safeguard the eye; they roll the eye into the back of the socket exposing a hardened pad at the rear of the eyeball. The existence of such strategies designed to protect the eye, highlight the importance of sight as a sensory function to the shark. Vision varies between species but generally speaking, in good visibility their range of sight tops out at around 20m.