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Vision

Vision

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This lesson will examine the structure of the eye and will identify how our brain processes visual signals.

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Tutorial

What's Covered

Welcome to this lesson today on vision. Today, you are going to be learning about the eye-- its structure and its function-- and the processes that happen that allow us to be able to see. Specifically, you will look at:

  1. Outer Parts of the Eye
  2. Inner Parts of the Eye
  3. How Vision Works
  4. Rods & Cones

1. Outer Parts of the Eye

The sclera is the white of the eye and is made of this dense, fibrous tissue that helps provide protection for the eye.The cornea is a clear extension of the sclera that covers the iris and helps to focus light by bending or refracting it. Then also in this front part of the eye here, we have aqueous humor. Aqueous humor is kind of this liquidity, gel-like substance that fills this space in front of the iris. It helps maintain pressure, and it also helps to transmit light to the lens as well. Then the conjunctiva is basically just the outer layer of the eye which consists of mucus and blood vessels that protect the outside of the eye.

The pupil can constrict or dilate to control the amount of light that enters the eye. If it's really, really bright outside and you're outside on a really bright day, this pupil actually constrict to allow a little bit less light in. Or if you're in a really, really dim room, your pupils will dilate to try and let more light in, so that you can see a little bit more clearly.

The lens is the part of your eye that helps to focus incoming light. As light enters in through you eye, it'll actually enter in through your pupil, which is right in front of the lens, and then it will hit the lens. Then, that light will be reflected towards the back of the eye.

Take a look at the image below to have a better idea about where these parts are located. 


The iris is actually the colored part of your eye.If your eyes are blue, or green, or brown, or hazel, that colored part that you're seeing is called the iris.

Did You Know

An interesting fact about the iris is that they're kind of like another set of fingerprints. The patterns and the colors and the variation in a person's iris are very unique to them. So it's a very individualistic part that can be used in some cases to identify a person, because they're very, very specific.

Terms to Know

    • Lens
    • A structure in the eye that focuses light to the retina.
    • Pupil
    • The black part of the eye through which light enters.
    • Iris
    • The colored portion of the eye.
    • Cornea
    • A layer that covers the iris and helps to focus light into the eye.
    • Aqueous Humor
    • Fluid within the eyeball that maintains pressure and transmits light.
    • Sclera
    • The white of the eye that aids in protection

2. Inner Parts of the Eye

Within the eye you you can find the vitreous humor which helps to maintain pressure, support the eye, helps the eye maintained its shape. The vitreious humor is similar to the aqueous humor but it's found behind the lens and there's much more of it.

The retina is within the back of the eye and is where light is focused to. The retina contains rods and cones, which are photoreceptors that help to process this incoming light and allow you to see images and colors.

The fovea is an area in the retina where vision is the sharpest and it's densely packed with all of these different types of photoreceptors. The optic nerve is the part of the eye that will then send information up to the brain for interpretation.

Terms to Know

    • Vitreous Humor
    • Fluid within the eyeball that supports the lens and the eyeball.
    • Retina
    • An area in the back of the eye that contains photoreceptors to absorb light.
    • Photoreceptors
    • Cells that detect light found on the basement layer of the retina; includes rods and cones.
    • Fovea

An area of the retina where vision is the most acute.

Optic Nerve

A nerve that sends impulses to the visual cortex in the brain where images are interpreted.


3. How Vision Works

The first major phase step in vision is light will entering as a wave through the pupil and the lens will then focus it on the the retina. Then, rods and cones, or those photoreceptors found in the retina, will help to process that information.

Rods and cones that are found within the retina are connected to the neurons that send visual information to the visual cortex. The axons from neurons within the retina converge to form the optic nerves that carry visual information to the cortex to be processed within the brain.

Terms to Know

    • Vision
    • The perception of light, images and movement by the eye.
    • Visual Cortex
    • The part of the brain that receives nerve impulses from the optic nerve.

4. Rods & Cones

Rods and cones contain visual pigments, which change their shape when different wavelengths of light are absorbed. Each color in the visible light spectrum, if you're familiar with the visible light spectrum, relates to a different wavelength of light.

Take a look at the image below to see the rods & cones. 


The wavelength of red or blue or green or purple or yellow are all different from one another. And these visual pigments change shape, depending on the type of wavelength that's absorbed. Visual pigments contain a version of the protein, opsin, plus retinal, which is derived from vitamin A.

Did You Know

If you've ever heard someone tell you before that eating a diet high in carrots will help with your vision, there is actually some truth behind that. Carrots are high in vitamin A, and retinal is derived from vitamin A.

Rods get their name because they kind of have a rod shape to them. Rods are what allow us to see in dim light and they allow for a more coarse perception.

IN CONTEXT
If you were to walk into a pitch black room, right away you wouldn't be able to see much around you. However, after they take a little bit of time to adapt they would allow you to be able to see in that darkness. You'd be able to make out coarse objects, and you'd be able to see a little bit in that room.

Cones, on the other hand, contain a different visual pigment and they allow for daytime vision and for you to be able to see in bright light. There's actually three different types of cones, red, green, and blue. The variation of the visual pigment relates to whether it's a red, green, or blue cone.

The reason that we can't see colors in the dark, if you think back to our rods, we can see coarse images in the dark and black & white. However, within a dark environment there isn't enough light to activate cones so we have a more difficult time processing colors.

IN CONTEXT
If you were to walk, again, into a dark room and hold up two different color of shirts, you wouldn't be able to tell the actual color of either of them. In order, again, to be able to interpret color, you need to be in the presence of bright light.

Big Idea

Rods and cones are the two different types of visual receptors that are found in your retina. They allow for dim light, coarse perception, daytime vision, and bright light and the difference in their shape is how they get their name.

Terms to Know

    • Rod Cells
    • A photoreceptor that detects dim light.
    • Cone Cells
    • A photoreceptor that detects bright light.

Summary

This lesson has been an overview on vision. Specifically, you learned about the structure of the inner and outer parts of the eye, and how vision works. Finally, you took an in-depth look at the rods and cones in your retina.

Keep up the learning and have a great day!

Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
  • Vision

    The perception of light, images and movement by the eye.

  • Cornea

    A layer that covers the iris and helps to focus light into the eye.

  • Iris

    The colored portion of the eye.

  • Lens

    A structure in the eye that focuses light to the retina.

  • Retina

    An area in the back of the eye that contains photoreceptors to absorb light.

  • Visual Cortex

    The part of the brain that receives nerve impulses from the optic nerve.

  • Rod Cells

    A photoreceptor that detects dim light.

  • Cone Cells

    A photoreceptor that detects bright light.

  • Fovea

    An area of the retina where vision is the most acute.

  • Photoreceptors

    Cells that detect light found on the basement layer of the retina; includes rods and cones.

  • Vitreous Humor

    Fluid within the eyeball that supports the lens and the eyeball.

  • Aqueous Humor

    Fluid within the eyeball that maintains pressure and transmits light.

  • Sclera

    The white of the eye that aids in protection.

  • Pupil

    The black part of the eye through which light enters.

  • Optic Nerve

    A nerve that sends impulses to the visual cortex in the brain where images are interpreted.