About vision has this to say relative to eye size:
Scientists say that a giant squid (Architeuthis dux) living in the depths of the ocean has the largest eyeballs of any living creature today. The typical giant squid's eye can measure up to 10 inches in diameter, about half the size of a basketball.
On land, the record for biggest eyeballs is held rather surprisingly by the ostrich. The ostrich eye has a diameter of about 2 inches, roughly the size of a ping-pong ball.
The largest eyeballs of any creature ever apparently belonged to an ancient marine animal, known as an ichthyosaur that lived millions of years ago. Scientific American reports that this undersea creature had eyes about the size of bowling balls, which enabled keener eyesight within murky ocean depths....