As you look out on the world you are seeing it with eyes evolved from the same common ancestor as all fish: Light enters at the cornea, passes through the pupil to the lens, which focuses it on the retina. The iris controls the amount of light entering the eye. The retina contains light-sensitive neurons that collect the information and send it along the optic nerve into the brain. There is much variation across the 20,000 species of fish in the world. Eyeballs and pupils change shape at will, ultraviolet light is discerned, reflective layers glow like cat eyes to see in the dark. But the tiny deep-water brownsnout spookfish wins the award for strangest eyes in the sea. The only vertebrate that has a reflective visual system, the larger typically-structured eye is attached to a secondary one that includes a layer of naturally-occurring mirrors, enabling the fish to see both up and down simultaneously. The spookfish isn’t edible (unless you’re desperate), but one of the crucial signs of freshness when buying fish is clear, not cloudy eyes that bulge a little. Those peepers are a delicacy in some locales, especially among Inuit children, who pop them like candy.