Which animal has the largest eyes of any living creature?

The giant squid has the largest eyes known in any living animal, reaching the size of a dinner plate. That is far beyond what a simple scaling of body size would predict, and the likely reason is not seeing prey but seeing a predator. Sperm whales hunt giant squid in the deep sea, where sunlight never reaches, and a swimming whale disturbs bioluminescent plankton, leaving a faint glow in its wake. Detecting that dim, diffuse light at a distance is exactly the task an enormous eye is good at, because a bigger pupil gathers more photons and a bigger retina resolves faint contrast better. Below a certain depth an eye that large earns nothing extra for spotting small prey, but it buys crucial extra warning of something very big approaching. The squid itself is otherwise poorly known, since it lives deep and was photographed alive only relatively recently.

Colossal squid, a separate deep-sea species, are heavier still and also have enormous eyes.