BBC Earth

Facts about sight

Beyond Human
  • Surprisingly, our eyes are sharper than a cheetah’s. But while our most precise vision is in the centre of our field of view, a cheetah sees most clearly across a long, narrow band – this allows it to spot prey anywhere on the wide open savannah.

  • Humans can only see some of the visible light in the world as there are parts of the spectrum we cannot see, like ultraviolet and infrared. But caribou (or reindeer) are one of the only mammals on Earth that can see ultraviolet light. This helps them to spot predators. To the human eye, an approaching wolf would be perfectly camouflaged against the snow, but to the caribou eye, there is a strong contrast between the white snow which reflects the ultraviolet light and the very dark wolves, which absorb it.

  • Dragonflies are master predators with a 90% capture success rate – a lion’s is around 40% and a shark’s 50%. They have the largest and possibly the best eyes of all insects – they can see the world in slow motion. Human eyes can capture about 60 images per second, whereas dragonflies can capture around 200 images per second.

  • Bioluminescence is light created by living organisms and it can be found in deep oceans and coastal waters. Most bioluminescence is blue – this is because blue has a shorter wavelength than red, so it can travel further through water and be seen more clearly.

  • All the eyes on Earth are the size of an orange or smaller, with one exception – the mysterious giant squid. Giant squids can grow up to 14 metres (46 feet) in length and their eyes can grow to the size of a human head.

  • Peregrine falcons are the fastest animals on Earth and can hit 180mph (289kmh) in a dive, so they have to have very sharp eyesight to match. They have excellent acuity thanks to their fovea, a feature which they share with human eyes. The higher the number of receptors in the fovea, the more acute the vision. Human fovea can contain 200,000 receptors per sq mm, but there are twice as many in birds of prey.

  • The Cuban boa hunts bats in the pitch darkness of caves. How? It can see in infrared which is invisible to human eyes, so it can detect the heat that the warm-blooded bats emit. But it doesn’t use its eyes to detect infrared – instead it uses the pits in its jawline which detect heat.