Generally, large eyes appear in animals who, during the course of evolution, adapted to living nocturnally or in environments with very limited light sources. And what kind of environment is probably the most lightless in the world? Lightless caves and depths of the oceans. Now, if we’re searching for an animal with biggest eyes, we need a big animal. Cave dwellers nowadays tend to be rather small, especially those who never see the light of day, while deep ocean houses some of the most amazing giants the world has ever seen. So, of all the known animals, the colossal squid Mesonychoteuthis hamiltoni, seen extremely rarely, has the largest eyes. It lives several miles below the sea surface and its 11-inch eyes help catch even the smallest glimmers of animal fluorescence.