The largest eye in the animal kingdom belongs to the giant squid (Architeuthis dux). This deep-sea cephalopod has eyes that can reach up to 10 inches (25 centimeters) in diameter, making them the largest known of any animal. The size of their eyes is an adaptation to their dark oceanic habitat, allowing them to detect light and movement in the deep sea. These large eyes help them see potential prey and predators in the abyss, enhancing their chances of survival in an environment where visibility is extremely low.