1. The Human Eye Structure & Function Abnormalities Dissection of the Eye
Lesson 23 - The Human Eye
The Human Eye
Structure & Function
Abnormalities
Dissection of the Eye
Other types of Eyes

2. The Human Eye Our eye is designed to gather light for vision
The eye does not “see” for us… but rather is uses light to create nerve impulses to send to the brain
It is our brain that turns that information into images that we “see”
We will discuss this concept in more detail latter on

3. Structures of the Eye Choroid Cornea Sclera Iris Pupil Fovea Retina
Lens
Optic Nerve
Ciliary Muscle
Blind Spot
Vitreous Humor

4. EYES vs. CAMERAS

5. The Cornea
The cornea is a clear, dome-shaped surface that covers the front of the eye
It is the first and most powerful lens in the eye's optical system
To keep it transparent the cornea contains no blood vessels
Instead, tears that flow over it and aqueous humor in the chamber behind it keep it nourished

6. The Iris This is the colored part of the eye: brown, green, blue…
It is a ring of muscle fibers located behind the cornea and in front of the lens
It contracts and expands, opening and closing the pupil, in response to the brightness of surrounding light

7. The Pupil The pupil is not really a structure at all
The pupil is the hole in the eye ball that allows light to pass into the eye and to the retina
It is the iris that controls the size of the pupil
A “dilated pupil” is actually a wide open iris

8. Lesson 23 - The Human Eye
Demonstration Time

9. The Lens
The lens is a fairly solid structure which can be flexed by the joining muscles around the periphery of the eye
The lens is stretched or relaxed to either make it thinner or fatter depending on the distance the eye is looking at
If working properly, the lens will focus light to a point on the retina

10. The Ciliary Muscle
The ciliary muscle is the controlling factor that dictates how fat or flat the lens will be
When contracted, the ciliary muscle pulls on the lens
causing the lens to become flatter so the light from far off images can be focused
When the ciliary muscle is relaxed, the lens pulls back to become more round and will focus on up-close objects

11. To the right is a magnified view from an electron microscope that shows “zonule” fibers attaching the lens to the ciliary muscle

12. The Vitreous Humor
The vitreous humor is a sack of clear gel like fluid that fills the interior of the eye ball
The vitreous humor serves two purposes…
It helps the eye maintain its shape by “filling” the hollow of the eye and preventing outside tissue from changing the shape of the eye
Provides a clear path for light to travel to the retina

13. The Retina
The retina is a “blanket” of photo recepting nerves that covers the back 2/3 of the eye
The retina is composed of millions of RODS and CONES which are photon activated nerves
The retina is the most delicate portion of the eye

14. The Optic Nerve
The optic nerve is the eyes link to the brain and to the body
It is the only other opening to the eye other than the pupil
The optic nerve is a channel that funnels all of the nerve impulses created by the photoreceptors (Rods & Cones) to the brain
The opening is also the chorid’s connection to the circulatory system for nourishment

15. The Optic Nerve The optic nerve has 4 main wires running to the brain
As you can see, two of the wires cross so that info seen from the right visual field is sent to the brain together and info seen from the left visual field is seen together
The optic nerves travel to the occipital lobe of the brain

16. The Blind Spot
Where the retina and nerves (wires to the brain) funnel out of the eye is called your blind spot
It is at the one area where there aren’t any photo receptors to be activated by light
Therefore we “don’t see anything” at this point

17. The Blind Spot

18. The Blind Spot
You can experience your blind spot by playing around with two images equidistant to your eyes and then covering one eye
Move the images back and forth until you can’t see one

19. The Sclera
The sclera is the white part of the eyes some of which you can see from the front of the eye
The sclera is the “flexibly rigid” portion of the eye that provides the eye with its shape
The muscles that move the eye up & down and side to side are attached to the sclera

20. The Choroid
The choroid is a black layering of blood vessels on the interior of the eye
The blood vessels provide the cells in the retina and the interior of the eye with nourishment
The black pigment is meant to absorb all the light that enters the eye

21. The Fovea
The fovea is a pinpoint space located in the center, at the back of the eye directly behind the center of the lens
The fovea is a concentrated node of photoreceptors (mostly cones) where the lens tries to focus the light on

22. Cones in the Retina
Cones are cells that are activated by bright light and allow us to see in great detail
Cones are mostly concentrated at the back of the eye directly behind the lens
Cones allow us to see colour

23. Rods in the Retina
Rods are cells that are activated in dim light and allow us to see at night time in low light
Rods are mostly concentrated around the periphery of the eye and provide peripheral vision
Rods see in Black & White

24. Lets Recap the Eye Choroid Cornea Sclera Iris Pupil Fovea Retina Lens
Optic Nerve
Ciliary Muscle
Blind Spot or Optic Disk
Vitreous Humor

25. Lesson 23 - The Human Eye
Your Task
You are being given a short worksheet that deals with the structures and the functions of the eye
Your task is to complete this sheet in a timely manner before we move on to the next portion of the lesson
Be sure to ask for help on any concept that is confusing you so that we can get it cleared up before your oral examination on the eye