Of all the human senses, the visual system—the network that turns light into neural signals that create the perception of sight—is the most studied and best understood. Our intense curiosity about sight is no coincidence; we are animals who judge the world mostly by appearances rather than, say, aromas. But our eyes afford us only one view out of a multitude of possibilities. In the depths of the ocean—a world we are beginning to learn about in detail, thanks to new views provided by unmanned submersibles—marine species have developed visual systems drastically different from our own.
Most eyes, whether on land or in the sea, share two basic components: something to focus light as it hits the eye (for humans, a cornea and lens), and something to absorb and detect that light (a retina). Then the divergences begin. Among ocean creatures, eyes have evolved a bewildering array of structures suited to each animal’s ecological niche and the depth at which it lives.
Some amphipods (deep-sea crustaceans) rely on biological fi ber-optic cables to send light to their retinas. Sight-dependent, ocean-roaming predators like the swordfish have excellent vision, whereas many creatures that live at great depths can make only simple distinctions between light and dark.
