Sharks have successfully prowled the oceans for millions of years, in part because of an impressive suite of sensory systems, including well-developed eyes and a large area in the brain devoted to vision.

But over the past few decades conflicting data have sparked a debate about whether sharks can see colors. (Related: "Color-Blindness Cured by Gene Injection in Monkeys.")

In a new study, scientists looked at the retinas of 17 shark species caught off the coasts of eastern and western Australia, including tiger sharks and bull sharks.

Retinas use two main types of light-sensitive cells to allow animals to see: