Vision misbeliefs won’t die

Vision misbeliefs won’t die

I’m still reading my book, The Eye: A Natural History, and finally in the last chapter. Wow, the information in it isn’t something that I can just take with a grain of salt. The reason it’s taking so long to finish is because I’m looking up so much about what I read in it. Vision and how the eyes work…there are still some mysteries to us and that mystery goes way back thousands of years. If we didn’t have to think about how things worked and went on our merry way, would we be any better off? Of course not, that wouldn’t be human (because of our curiosity for answers) but the fact that 50% of college students think that light goes out of our eyes to see rather than coming in to our eyes is just hard to believe. Superman eyes? Really, there’s a study that showed half of the college students surveyed think light comes out of our eyes so that we can see.

This is called emission theory. Not sure why it’s called a theory in wikipedia. But it was a theory hundreds and thousands of years ago. One of our great philosophers believed that, Plato. I can’t imagine what people thought a thousand years ago but things still persist. Things and thoughts were written down so that makes a lot of what someone believed to have a persistency….because it’s written down. The information does not go away or get retracted. It’s like some news reports we hear or read where something sensational happened and it made headlines. There are many occasions where the later final report clarified what actually happened in that sensational story but didn’t make headlines, rarely ever makes headlines or is even reported….unless it’s another sensational story.

Why would 50% of college students think that light comes out of our eyes to see things? I’m beginning to really wonder if Superman does have anything to do with that. Maybe there’s another situation that might reinforce this which is when a little baby plays peekaboo. If their eyes are covered they think the other person has disappeared. They don’t understand object permanence but does that linger into college in some other way?

Another interesting experience is seeing the reflection of light come out of an animals eyes at night. It’s called eyeshine. You probably know what that looks like….beams of light coming out of a cat, deer or a raccoon’s eyes. Perhaps those animal reflections are unexplained to younger people so they might believe light does come out of an animals eyes to see better. And in reality, it does come out but only because light was shined into their eyes. They have interesting retinas with tapetum lucidums that give their photoreceptors a second chance to receive light by it reflecting back instead of the light just being absorbed. Even humans have reflecting retinas, “eyeshine,” that give us a red pupil after a camera flash. See my other post about that.

Is this light coming out of eyes related to the so-called “evil eye” where one could inflict some torturous occurrence to another by staring at them? What eyes say to others is another story but you can get the feeling when someone is giving you that look. They aren’t sending any light out of their eyes to you though.

One other misconception I want to mention is that you can still drive a car if you’re dilated! I wanted to get that in here. So many times patients ask me if they can drive home after I dilate them. There are a few exceptions to this but for most people dilating isn’t anything to worry about, driving or not.

And finally, light does not come out of our eyes to see objects. It comes into our eyes. You knew that.

A website with a fun read about ancient belief of light coming out of our eyes.

Here are some cool eyeshines (color of the reflection has to do with the angle and mineral structure):

frog eyeshine deer eyeshine spider eyeshine

cat eyeshine

cat eyeshine

 

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What can a paleobiologist do with a Trilobite eye?

What can a paleobiologist do with a Trilobite eye?

I’m still reading this book, The Eye: A Natural History, by Simon Ings. I keep getting sidetracked by all the interesting things I find in it and so my amazon.com wish list is getting longer with books I want to read. So, the trilobite, what an ancient critter. There were huge numbers of them, a prolific species living in the oceans between 250 and 500 million years or so ago…but now extinct so there are no living ones today. Apparently the Permian–Triassic extinction event killed practically everything, I mean upwards of 90% of every living animal it’s estimated, around 250 million years ago,  eventually died. The little trilobites weren’t fit for whatever nasty events happened that long ago (look up Siberian Traps). But we have their fossils and in particular there’s one genus of trilobite called Phacops that was studied by Dr. Kenneth Towe, who is a paleobiologist at the Smithsonian Institution, which had something about it’s eyes that interested me.

These Phacops trilobites and other trilobites had eyes unlike most animals except our present day brittle star (which is similar to a star fish). It had something like compound eyes found in present day arthropods like insects. How vision worked for something that lived hundreds of million years ago is pretty hard to know but eyes are basically light detectors attached to a nervous system. Eyes were and are soft tissue in animals past and present so they are not the kind of stuff that usually fossilizes. But the eyes of a trilobite had a mineral crystal for it’s focusing lens and it’s no longer thought that the crystal developed because the trilobite fossilized. It’s clear that that was what the trilobite had in it’s eyes when it was alive. Guess what you can do with it now? You can look through it! You can look (with a microscope or other setup) through an animal’s eye that lived about 400 million years ago. Crazy!

The crystal lens in the Phacops eye is made of calcite, a calcium carbonate mineral that is optically clear, like glass. We don’t know why or how the genetics worked in this organism to produce this. But what I also find interesting is what this mineral, calcite, can also do optically. Have you ever heard of Iceland Spar or heard of the optics word, birefringence? I’d never heard of Iceland Spar before (I want some) but I do know about birefringence. Birefringence is an effect that occurs in a transparent material where it causes an image to double. I think the pictures below will explain what birefringence does. Also look at the photographs Dr. Towe took looking through a Phacops crystal lens. Back in 1973 he took pictures of smiley faces that he drew and a picture through a Phacops lens of a building across the street from his office in Washington, DC. It’s also interesting to note that in our own eyes we have a crystalline lens (we call it that….unless you’ve had cataract surgery) but it’s a cellular structure, not a calcite crystal rock. It’s not at all related to a rock, but we still call it a crystalline lens. There are a lot of different types of eyes in our world that suit a particular animal and the trilobites had a very unique type of optic material.

What an amazing feat though. Finding a fossil, finding the tiniest little particle, a crystal, and then being able to look through it. It’s just incredible what we can find if we spend some time to look at the details or even the larger perspective how things existed on this planet through the study of geology and fossils and my favorite, astronomy (of course, the other sciences too). There will be a lot of astrobiologists and other scientists looking at what might exist on other planets and how those organisms, if we find any life, live in their particular environment. The trilobite could be somewhere living on another planet. Who knows?

Thank you to Dr. Kenneth Towe for corresponding with me and providing some of his research regarding the Phacops trilobite.

 

Iceland Spar

Iceland Spar

 

calcite

calcite

trilobite smiley face

trilobite smiley face

Building seen through phacops

Building seen through Phacops

 

 

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