A&P 1 Eye & Vision Lab –

Vision Concepts

In this "Lab Exercise Guide", we will be looking at the basics of vision. NOTE: these notes do not follow the order of the videos. You should be able to read this and understand the important concepts.

Your Prelab notes have the details of what you need to know for the Practical!

Welcome to a lab where physiology is important! There are questions in a STUDY GUIDE to help you get ready for the lab practical, along with some links to review videos.

I. Vision and the Eye

- What is vision? Perception of light! Light is an energy. - But…what do we use it for? Detect a pattern:

Decision: do we need to react to what is out there? Move towards, away from, or FREEZE! Boundary Movement

Deers get hit by cars

a lot because they

assume the car is

coming straight at

them!

1. Light is an energy 2, Light is fast 3. Light travels in waves 4. But light behaves as “matter”, in that it “bounces” …. it undergoes “reflection”: it bounces at a predictable angle! But obviously, sight is more than the mere presence or absence of light; our nervous system uses this information to tell us about size, shape and movement. And, humans have very good vision. We use it for recognition (more than smell, which is what most animals us). Our vision is heightened in 2 ways:

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1. Color: helps us focus even finer What does color vision give us? Ability to see a boundary or edge with great accuracy!

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NOTE: “colors” are different wavelengths in the visible spectrum. We will deal with color vision in the “Vision Testing” lab.

But not all animals have this ability. And some animals see other parts of the spectrum.

B&W

Both black and white are not colors. They are the presence of all waves (white) and the absence of all waves (black).

Other

animals

Birds are tetrachromatic (4 colors). They can see ultraviolet. This is a bird’s visual spectrum: MYTH: cats can see infrared. Cats and dogs can see more ultraviolet than us, but it is because our lens filters it out!

A lot of animals, including cats, are Dichromatic (2 colors). They see fewer colors. Very few mammals outside of primates are trichromatic.

The reason warm blooded animals can't normally see infrared is we give off so much heat it would blind us, the eyeball being inside the body and it'd be useless.

Snakes

Some snake’s Pit Organ

“Pit vipers”

The ability to sense infrared thermal radiation evolved independently in several different families of snakes. Essentially, it allows these animals to "see" radiant heat at wavelengths between 5 and 30 μm to a degree of accuracy such that a blind rattlesnake can target vulnerable body parts of the prey at which it strikes.

Learning

colors

We are born with the ability to see black and white. We are not born with an understanding of color. We LEARN to ID our colors!

Since a “color” is what our brain puts there in order to identify wavelengths, we probably see colors differently Good article on the science behind this: https://www.livescience.com/21275-color-red-blue-scientists.html

Tetrachromatic

?

Tetrachromacy On 28 February 2015, an online test for tetrachromacy (a rare condition of a person’s having four cone cells in the eye) went viral after being shared on the LinkedIn social media site. The test, which was posted just a few days after the Internet became obsessed identifying the color of a dress, asked viewers to count the number of colors in an image. The amount of colors perceived supposedly indicated the number of cones the viewer possessed. Those who spotted more than 32 colors were informed that they had a unique fourth cone and were therefore tetrachromats Thousands of people took the test and proudly shared the news that they were tetrachromats on Facebook and Twitter. The majority of those people, however, actually didn’t see an unusually high number of colors. According to the researchers at New Castle University’s Tetrachromacy Project, standard RGB (i.e., red-green-blue) computer monitors are not capable of displaying the range of colors required to create a reliable online test for tetrachromacy.

Additionally, the claim that 25% of people are tetrachromats is inaccurate. While Jay Neitz, a color

vision researcher at the Medical College of Wisconsin, estimated that half of the female population has

a fourth cone in their eyes, only a small number of those people can actually see additional colors.

Newcastle University neuroscientist Gabriele Jordan said that the number may be higher (about 12%), but in twenty years of research she has only been able to confirm the condition in one person:

“We now know tetrachromacy exists. But we don’t know what allows someone to become functionally tetrachromatic, when most four-coned women aren’t.” In other words, you can have 4 cones and not be tetrachromatic. It seems you have to be a woman who is heterozygote for a mild form of color-blindness.

Depth

Perception

2. Two eyes pointed forward: gives us Depth Perception NOTICE: the retina is just one thin layer of cells; it is like a movie on a screen.

- Notice: Your vision is 2-dimensional - just like a movie on a picture screen!! But your vision is in 3 dimensions, isn’t it? No ... this is an optical illusion, caused by the fact that you have 2 eyes, each of which is seeing the image at a slightly different angle. * NOTE: some semesters, we do the brain AFTER the eye. Please make note of the optic chiasma in the “brain” lab!

Blurry

vision

Most blurry vision comes from an inability to control the muscles. Drugs that act as muscle relaxants cause blurry vision.

Scientific fact: All pirates lack depth perception!

Reflected

light

We TRANSDUCE REFLECTED LIGHT - This forms an IMAGE on the retina. The pattern on the retina is sent to the brain for processing. Lenses “flip” an image. The brain “un-flips” it for us!

Visual

field

This gives us a “visual field”

- In order to do this, we must be able to perceive the “edge” or “boundary” of what we are seeing. In other words, we must be able to FOCUS (= distinguish a line). “Acuity” is the ability to focus. “Accommodation” is the ability to change focus as something moves. We focus the object we want to “pay attention to” (is it moving towards us? Is it important?) on a special area called the macula luteum. The rest is “peripheral vision” and is not focused.

Black

Box

So: In Summary: Eye is a black box, with “film” (retina) on the back wall The coat deep to the retina, the choroid, absorbs the light so the retina has time to “pick it up”. The photoreceptors pick up the image. The info is then sent to the brain via the optic nerve.

Shape

The shape of the eye (and the individual parts of the eye, like the lens) is EXTREMELY important if we are going to be able to focus correctly. The vitreous humor slows light down, and maintains the shape so the lens can focus onto the macula.

Important

Parts

The sclera is the outer protective layer. Thick, hard to get through. The cornea is a transparent extension of the sclera, so light can pass through. Behind the cornea, in front of the iris, is a chamber called the anterior chamber. It contains aqueous fluid. glaucoma Light then passes through the pupil, entering the black box. Light of main interest is focused onto the macula lutea. All other light hits the rest of the retina as peripheral vision..

Focus

Macula lutea = Dense cells. Can’t be seen on a gross level. The specific point where you are pointing your eyes is on the central fovea centralis (sharpest vision).

The fovea and macula composed of cones ONLY! The human eye is sensitive to light between roughly 380 and 740 nanometers. On a typical retina, there are 10 million rods for sensing low light levels and 5 million cones for detecting color. Our vision is really set up for facial recognition. It is not a coincidence that our macula sets up a sharp in-focus field of about the width of a person’s face if we are standing a couple of feet away.

Macular degeneration

This is where we,

in the western

world, look for

“social talk”.

Eye

Contact?

Myth: we look in someone’s eyes to “convince them” or to “speak seriously”. We interpret “looking in the eyes” as “dominance” or “aggression”. That usually turns the person off, and makes them less likely to listen to what you are saying. Looking in someone’s eyes means “I want to move towards you”. May be aggressive or romantically. We actually look AWAY from the eyes when we are listening or are being serious. In the western world, it is “up”.

This is where we,

in the western

world, look for

“business talk”.

Accomodation

Accommodation is accomplished by changing the shape of the lens using the suspensory ligaments, which attach to the ciliary body.

Optic disk

Blind spot

The optic nerve transmits the image pattern to the brain. Optic disk and “blind spot” in your vision.

Iris

The iris is a sphincter muscle (smooth” that controls the size of the pupil, allowing more or less light into the “box”.

Eye

color

Muscles

Extrinsic muscles

Conjunctiva

A special membrane called the conjunctiva

Not seen

on models Conjuctivitis

Reflected

Light

Don’t forget the “Eye Slide” – best seen at lowest power possible (unless looking at the retina/choroid)

Where is the “red”? This pigment absorbs all colors except “red”. So the red is bouncing back and hitting your retina. The red is not here. It is in your eye. This box contains all light waves EXCEPT red. Of course, that information is not useful to us. So we say “the box is red”. More on colors, and what they are used for, latter!

Plants

Note for the science nerds: Plants can only use red & blue light waves for photosynthesis! The green is “in your eye”, because they are absorbing the red and blue. Chlorophyll absorbs red, orange, yellow and blue. In the fall, the leaves begin to die. They lose their chlorophyll, and slowly stop using the red light. So now, you can see it! But, the plant cell walls and other structures absorb “blue”, so you never get to see that! Flowers don’t do photosynthesis, so they can be blue!

Pupil

Why is the pupil always black? Tapetum lucidum

Eye

exam

Eye exam with an ophthalmoscope.

Detail

Why, on an eye exam, it the macula dark and the optic disc white?

degeneration

Interpretaion

“behind”?

Also notice: as the subject gets closer to the eye, the image on the retina gets bigger (that is, more receptor cells are activated)! This is interpreted as movement towards the observer.

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Vision

Memory

Oddly, your vision is a MEMORY of what the brain perceived The brain is deciding what you’re going to perceive, and it’s processing all of the information and then it’s determining what the best interpretation is.

http://journals.sagepub.com/doi/10.1177/0956797613502814

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Here, the proximity of light and dark squares as well as soft shadows fools the brain into making the wrong judgments. Read more at http://blog.visme.co/best-optical-illusions/#rb8bmc5A9q6Ax1XF.99

But, of course, now that I’ve shown you the truth, you can see it, right?

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