Ostrich eyes aren't just the biggest of any bird - they are the biggest of any animal on land. Each eye measures close to 2 inches across. That’s about as large as a billiard ball and even larger than the bird’s own brain.
They take up so much room in the skull that the ostrich's brain is actually smaller than either one of its eyeballs. This may be why the ostrich, despite its tremendous running speed, is not very good at eluding predators: It tends to run in circles.