Are your eyes so tough you animal are your eyes very tough
July 20, 2012 11:36 AM   Subscribe

Which animal has the hardest eyes? I was thinking about how eyes are pretty soft and it might be advantageous for a creature to have "natural goggles" protecting its squishy eyes. Which animal's eyes have the toughest coating? (I do not care to hear about the protective qualities of retractable eyeLIDs, only the surface which can not be retracted, and which must be seen through.)
posted by Greg Nog to Science & Nature (12 answers total) 8 users marked this as a favorite
Deep-sea creatures, presumably. Like viperfish. They live about a mile down, i.e., at pressures that would compress all the air out of your body and go a long way towards flattening your bones.
posted by valkyryn at 11:44 AM on July 20, 2012

Except deep sea creatures don't have air in their body. Nor do they have air in their eyeballs. Actually, I don't think any creatures have air in their eyeballs, so I'm not sure how the ambient pressure is relevant here.
posted by Grither at 11:48 AM on July 20, 2012 [1 favorite]

here ya go. Everything you would want to know about nictitating membranes.
posted by HuronBob at 11:51 AM on July 20, 2012

Deep-sea creatures, presumably.

Water is essentially incompressible, so there's no need for their eyes to be unusually tough. They aren't pressure vessels.

Trilobites had lenses made of calcite, which isn't a very tough mineral (3 on the Mohs scale), but probably hard enough to scratch a vertebrate eye. There's a living species of brittle star that has calcite lenses. I don't know if the lens was the outermost structure in those eyes or if they had a separate, less-tough cornea.

However, regular eyes are tougher than you might think. The human eye is under a bit of pressure, which keeps the outer structure nice and taut. The outer structures (the cornea and sclera) are fairly tough, about like leather of a similar thickness.
posted by jedicus at 11:53 AM on July 20, 2012 [2 favorites]

Some animals have bone-reinforced eyes, which seems pretty damned hardcore to me. The normal sclera is tougher than you'd think, though - I thought they were all weak and squishy until I had to dissect one.
posted by julthumbscrew at 12:03 PM on July 20, 2012 [2 favorites]

The barreleye fish has its eyes set inside a transparent skull. Does that count?
posted by wolfdreams01 at 12:24 PM on July 20, 2012 [7 favorites]

Chitons' eyes are made of aragonite, another form of the same substance that makes up calcite. It's harder than calcite, though (3.5-4 on the Mohs), so I'd say they are the current winners, depending on how you define toughness.
posted by jedicus at 12:45 PM on July 20, 2012 [1 favorite]

Lobster eyes are likewise mineralized.

It's possible that an animal with pinhole camera eyes (like the cuttlefish) would win this title, since the material leading up to the pinhole doesn't need to be transparent.
posted by IAmBroom at 1:29 PM on July 20, 2012

cuttlefish don't have pinhole-camera eyes.
posted by russm at 4:43 PM on July 20, 2012

I think there was some confusion between cuttlefish (which don't have pinhole eyes) and nautiluses (which do).
posted by jedicus at 5:54 PM on July 20, 2012

I don't know how close it is to being the toughest, but snakes' eyes are covered with the same stuff as the rest of them. When they shed, the eyecaps come off with the rest of the skin, in one piece. They don't have eyelids, of course, and some species burrow with no way to protect their eyes from whatever they may run into. So, pretty sturdy, anyway.
posted by Because at 9:31 PM on July 20, 2012

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