A closer look at that freaky, giant fish eye

Last week, Mark told you about a giant eyeball that washed up on the beach in Florida. Today, the Florida Fish and Wildlife Conservation Commission released their preliminary analysis of who that eyeball once belonged to and how it likely ended up becoming the temporary toast of the Internet.

The Deep Sea News blog called it last week, but the official word from the experts is that this was the eye of a swordfish. The distinction is based on the size, the color, and the fact that there are bits of bone present around the edges (something you wouldn't see attached to a giant squid eye).

How do you get a swordfish eye without a swordfish attached? Simple: It's swordfish season. In the press release, Joan Herrera, curator of collections at the FWC’s Fish and Wildlife Research Institute in St. Petersburg, said that, "Based on straight-line cuts visible around the eye, we believe it was removed by a fisherman and discarded."

But before we pack this mystery away, I think you should take one more close look at the giant eyeball, because it offers a great view a really interesting feature of fish eye anatomy. Fish eyes are similar to those of land-dwelling vertebrates. But there are some key differences. In particular, the shape of the lens...

In the human eye, you've got an iris, you've got an opening in the iris called the pupil, and you've got a flattish lens sitting behind the pupil. In a fish eye — including this one &mash; the lens is much more rounded and it sticks up through the pupil like a little nubbin.

In 2007, Advanced Aquarist magazine had a feature all about fish eye anatomy, which explained how this anatomical difference affects the way the fish eye works.

A prominent characteristic of the fish eye, from the outside at least, is its bulbous nature. Some of the reasons for this will become apparent. The outer layer of the eye, the cornea, is dome-shaped and transparent. It is the first to receive light. With the terrestrial vertebrate eye, light travels through the air and hits the cornea. Because the air and cornea are of differing densities, the light is refracted (bent and directed) into the opening called the pupil. Water and cornea are of about equal densities so there is little refraction with the cornea of a fish eye. Again, with terrestrial vertebrates, the iris is the colored aperture that opens and closes, adjusting the size of the pupil and the amount of light entering the eye.

But in most teleost fishes, because of the protruding lens, the iris is rigid, making the pupil a fixed size. Therefore, to compensate for the amount of light entering the eye, an amount which could be too intense or not intense enough to measure, the retina adjusts the position of the photo receptors. And whereas our terrestrial eyes adjust to light levels within a few moments, fish eyes take much longer. We can observe this in aquarium fish that have been subjected to suddenly having their tank light turned on. Such fish typically hide until their eyes have adjusted to the light, which can take fifteen or twenty minutes.

Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.

Maggie goes places and talks to people. Find out where she'll be speaking next.

MORE: anatomy • fish eye • florida • meme • physiology • Science • swordfish

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Boundegar

I still say it’s Wheatley.
http://twitter.com/digitalArtform Joseph Francis

I’ll keep an eye out for ya
- http://twitter.com/digitalArtform Joseph Francis
  
  They caught my eye?
  
  :D
  - Chris Gladish
    
    Eye see what you did there.
http://twitter.com/cicadamania Cicada Mania

Another neat thing about the swordfish eye (and tuna and some sharks) is that it is self-heating.
- Rich Keller
  
  That way their eyes don’t fog up when they jump out of a balloon from space.
  - acerplatanoides
    
    I wonder how whales manage?
    - robotnik
      
      Well, it takes an awfully big balloon.
      - acerplatanoides
        
        or a lot of little birds?
      - smut clyde
        
        African or European swallows?
    - Brainspore
      
      Such an occurrence seems highly improbable.
      - Felton / Moderator
        
        Infinitely improbable, one might say.
      - robotnik
        
        Hope springs eternal.
      - acerplatanoides
        
        Clearly you are not a respected physicist. Good day, sir.
Just_Ok

Call me, is my eye
emschelle

Now I feel bad for turning on the light in my aquarium.
Brainspore

Lies. That is clearly just one of the many horrific eyes cast off by a Shoggoth. To merely gaze upon such a thing is to court madness.
- acerplatanoides
  
  Fo’ R’lyeh
gjbc

Hmm… now I’m inspired to make a SCR controlled time-dimming light switch for my goldfish. Seriously. A great project that I expect to see in Make Magazine soon.
- http://www.facebook.com/profile.php?id=507325475 Steve Bedi
  
  My thoughts exactly. Million dollar invention? Lets get to work!
Mark Dow

How can “the retina adjust the position of the photo receptors” in such a way to reduce incident light?
Michael Tanaka

I was expecting to see a joke about how you get a swordfish eye with out a swordfish. This is what I would of written. “How do you get a swordfish eye without a swordfish attached? Simple: They are swordfish, someone was bound to get an I poked out.”
monkey magic

Looks like one of those ceramic speakers.