Central Retinal Artery: A Brief History
The human eye consists of two main parts: the front part (the retina) and the back part (the optic nerve). The retina contains light sensitive cells called photoreceptors. These are responsible for our ability to see color.
The optic nerve connects the retina with the brain.
In order to make sense of what we see, it helps us to have some sort of visual memory. That’s why we need a way to remember things like where something is located in space or how far away something is from us. This is where the brain comes into play and uses images stored in our memories to create new concepts and ideas about objects in our environment.
The brain has several ways of storing information. One method is through long term storage such as in your hard drive. Another method is short term storage such as in the form of temporary files on your computer’s hard disk.
Short term memory stores only those pieces of data that are needed right now and then immediately deletes them when they no longer are needed. Long term memory on the other hand, stores those pieces of information that you want to keep for future use and never deletes them.
The human brain is divided into two sides or hemispheres. Each side of the brain controls a different set of abilities. For example, the right side of the brain controls the ability to move your body’s right side and to recognize visual information, such as a person’s face or the written word.
The left side of the brain controls the ability to move your body’s left side and recognizes visual information, such as a person’s face or the written word.
In addition to the two sides of the brain, there are two kinds of vision fields in each eye. One is a horizontal field that detects movement from one side of your body to another; this is called the “straight ahead” field of vision. The other field of vision is a vertical or up-and-down one that detects motion from your shoulders to the tips of your toes; this is called the “peripheral vision”.
The point where these two fields meet is called the “fovea”. The fovea contains the highest density of light-detecting cells in the retina and is responsible for sharp clear vision. This is why you should look at objects that you want to see well directly with your eyes and not through the use of binoculars or a telescope.
Because the fovea contains the highest density of light-detecting cells in the retina it can also become damaged if you’re exposed to too much bright light. This can cause a temporary or permanent loss of your ability to see fine detail. But because humans have two working eyes, chances are that the other eye will still be able to provide enough visual information for you to see well enough to function normally.
The retina is the inner lining of the back of the eye. It receives light through the pupil, converts it into electrical signals, and then sends these electrical signals through the optic nerve to the brain for processing.
The blind spot is an area in each eye where the optic nerve connects with the retina. The reason we don’t normally see “black spots” in our vision is because the brain fills in the gap with surrounding visual information. If we close one eye and look at a sideways “E” held at arms length, however, we can actually see the blind spot in our vision quite easily because the surrounding visual information no longer “fills in the gap”.
The lens of the eye focuses light onto the retina. This is similar to the way a camera focuses light onto the film inside it. The lens in the eye can also change its shape, thus letting us adjust the focus from objects that are close by to objects that are far away.
The iris of the eye (the part that you can see) is colored, but has no other function other than to control the amount of light entering into the eye.
The pupil is the hole in the center of the iris that lets light rays enter into the eye. When there is a lot of light, the pupil gets smaller to limit the amount of light and improve the quality of the image formed on the retina. The pupil also gets smaller in response to very dark surroundings.
This is why it’s easier to see at night if you face a bright spot (like the moon) rather than looking out into a sea of darkness.
When there is not enough light, the pupil gets larger to let in more light. The iris contains a number of small muscles that can contract and dilate the pupil. These muscles are under our conscious control, but they also react to various chemicals and light.
These are pictures that look one way at first, but after a period of time, they look another way. This is a good test to see if you’re paying attention!
This is a way of “visualizing” what someone sounds like. It takes a little practice, but it’s pretty easy. Just pick someone you know and read the words below while imagining what they sound like.
Imagine that you’re waiting in a line at the bank and suddenly you hear the person in front of you break into song.
What do they sound like?
Blue: Green: Black:
What do you see?
Green: Blue: Black:
Now, that wasn’t too bad, was it?
Please post your impressions on the bulletin board.
Want to try another?
OK! Pick a friend or relative and try again.
Imagine that you’re sitting in a college classroom. It’s nearly exam time and your mind is definitely not on the lecture. The person sitting next to you is busy taking notes and paying attention.
What do they look like?
Grey: Blue: Black:
What are they wearing?
Blue: Black: Grey:
No peeking at the colors this time! After you’ve picked an outfit, look at the color list and see if your choice was right.
Lets try another… This one is a little weird, but pay attention to what you see in the picture….
After looking at the picture for a while, you may start to notice certain things. The black spots on the grey log are in the shape of a face. The blue thing on the right looks like an eye and there’s another on the ground.
Turn the picture upside-down and the eye on the ground is now a mouth. Now turn it sideways and you can see that what looks like two sides of a hill, is actually two arms raised in anger.
There’s even more hidden in the picture if you look hard enough!
This one is really easy. Look at the picture and see if you can tell what color each square in the picture is.
After you think you’ve got it, scroll down and look at the answer. There are more than you think!
Now it’s your turn… Think of a color (it doesn’t have to be one of these).
Count out that many squares starting with the first one and see what color it is. For example, if you think of “orange” count out the first orange square.
The answer is at the bottom. Find the color and how many squares it took you to find it.
Count out ____ squares and find the color. Don’t cheat!
Did you get the same answer or a different one?
You can also try different colors.
Did the same one come up a lot or did it change? Were you surprised by what color it was?
What does this mean?
We’ll talk about this next week.
First, lets give a big hand to Carla for that great illusion! (Make sure you clap loud so she knows you’re here!)
Now, let’s talk about what we just saw.
What did you think of the illusions? The first one was pretty easy, right?
But after that, they got harder.
How did you do? Think you could figure them out?
Don’t worry if you didn’t get them all right… Carla didn’t either!
says Carla. “I thought I did pretty well!”
Well, you’re right, but you could have paid a little more attention to the lecture! You already knew most of the stuff that was in there. The illusions were a fun way to tie everything together.
This week’s lecture covered the following:
The difference between near and far focus .
and . The importance of color.
How illusions work.
How to figure out an illusion using what you know.
One more thing: You can still see the 3D images in “Space Dust!” and “Magic Eye” if you look at the right place.
What about the other one?”
says Carla, “I looked at it and couldn’t see anything!” That one didn’t have a three-dimensional image; it had hidden pictures in it!
This week, you learned about _____________.
Next week’s lecture is the last one! I can’t wait to tell you about ________.
If you think you already know everything about _______, and you’re right, then I’ll just pick something else to talk about instead. But I really think you might like to hear about this.
And don’t forget: bring your tickets to the show this weekend!
See you next week.
Sources & references used in this article:
Central retinal artery occlusion and retinal tolerance time by SS Hayreh, HE Kolder, TA Weingeist – Ophthalmology, 1980 – Elsevier
Central retinal artery obstruction and visual acuity by GC Brown, LE Magargal – Ophthalmology, 1982 – Elsevier
Central retinal artery occlusion: visual outcome by SS Hayreh, MB Zimmerman – American journal of ophthalmology, 2005 – Elsevier
General caliber of the retinal arteries expressed as the equivalent width of the central retinal artery by JC Parr, GFS Spears – American journal of ophthalmology, 1974 – ajo.com
A review of central retinal artery occlusion: clinical presentation and management by DD Varma, S Cugati, AW Lee, CS Chen – Eye, 2013 – nature.com