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:

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

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

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

Birds are tetrachromatic (4 colors). They can see ultraviolet. This is a bird’s visual spectrum:

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.

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

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!

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

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!

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.

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.

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.

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..

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”.

Accommodation is accomplished by changing the shape of the lens using the suspensory ligaments, which attach to the ciliary body. The optic nerve transmits the image pattern to the brain. Optic disk and “blind spot” in your vision.

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

Extrinsic muscles

A special membrane called the conjunctiva

Conjuctivitis

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

Why is the pupil always black?

Eye exam with an ophthalmoscope.

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

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.