The Colossal Squid has the largest eye in the animal kingdom. At up to 11.8 inches (30 cms) in diameter, experts often describe it as the size of a dinner plate or, in other words, as big as a human head or basketball.

The Colossal Squid is the largest invertebrate known to science; it also has the largest eyes in the animal kingdom. Besides each one of the Colossal Squid’s eyes being up to 11.8 inches across, each eye has a lens the size of an orange. The huge eyes allow the squid to see in dim light conditions, very useful for an animal that spends most of its time hunting at 2000 meters below the surface.

It must also be mentioned that only sub-adult Colossal Squids have been captured and studied by man. It is believed that a full-grown Colossal Squid may grow up to 15 meters long. These giants must have even bigger eyes. Unlike the Giant Squid, the Colossal Squid has stereoscopic vision, having a greater ability to judge distances. Even more amazing, each eye has a built-in 'headlight', an organ known as a photophore which can produce light so that whenever the Colossal Squid focuses its eyes to the front, the photophores produce enough light for the squid to see its prey in the dark.

More Info: en.wikipedia.org