The giant squid sees the world with eyes the size of soccer balls. They’re at least 25 centimetres (10inches) across, making them the largest eyes on the planet.
Why does the giant squid have a champion eye that’s at least twice the size of the runner-up?
Dan-Eric Nilsson and Eric Warrant from Lund University, Sweden, suggest that the world’s biggest eyes evolved to spot one of the world’s biggest predators – the sperm whale.
Using a mathematical model, they found that in the deep ocean, eyes suffer from a law of diminishing returns. Small eyes can see dramatically further if they grow a bit bigger.
Using their model, Nilsson and Warrant found that enormous eyes have advantages over eyes that are merely large. Specifically, they’re much better at spotting other large objects that give off their own light, in water deeper than 500 metres. There’s one animal that fits those criteria, and it’s one that giant squids really need to see: the sperm whale.
But in the dark oceans, how could the squids see them? Nilsson and Warrant note that while sperm whales don’t produce their own light, they frequently disturb animals that do. When they dive, they knock tiny animals like jellyfish and crustaceans that flash in response.
These shimmering outlines would be too faint for most animals to see, but not the giant squid. Nilsson and Warrant showed that its huge eyes could pick up this light from 120 metres away, and they can scan a huge sphere of water for those tell-tale flashes.
From: http://blogs.discovermagazine.com/notrocketscience/2012/03/15/giant-squid-what-big-eyes-you-have-all-the-better-to-spot-sperm-whales-with-my-dear/
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