1. Sensory
Organs
The Eye
Free Powerpoint Templates

2. Sensory relationships
All of our senses respond to stimuli in the environment
Each sense has its own specific organ
In each sense organ there are specific sense receptors cells
The role of sense receptors is to register stimuli in the environment and to provide the other parts of the body with information about these stimuli

3. Sense organs (Fill out the following table)
Perception
Taste
Tongue
Salty, sweet, spicy, bitter

4. Sense organs Sense Organ Perception Taste Tongue
Salty, sweet, spicy, bitter
Smell
Nose
Nice odours, foul odours
Hearing
Ear
Quiet, loud (intensity), tone
Feeling
Skin
Soft, rough, smooth (texture)
Seeing
Eye
Light/dark
Colours, movement

5. The Eye The eye is the organ of sight
Our eyes enable us to appreciate:
Lines
colours
light properties
movements of the things around us
The eye is made up of a system of 4 membranes and 3 transparent substances

8. Anatomy of the Eye Membranes:
- 1 membrane covers the front part of the eye  the cornea
- it is transparent
- under the cornea are:
1) The iris : the coloured
ring of the eye
2) The pupil: the central
portion of this ring
(black dot)
The eye is the organ of sight, a nearly spherical hollow globe filled with fluids (humors). The outer layer or tunic (sclera, or white, and cornea) is fibrous and protective. The middle tunic layer (choroid, ciliary body and the iris) is vascular. The innermost layer (the retina) is nervous or sensory. The fluids in the eye are divided by the lens into the vitreous humor (behind the lens) and the aqueous humor (in front of the lens). The lens itself is flexible and suspended by ligaments which allow it to change shape to focus light on the retina, which is composed of sensory neurons.

9. Anatomy of the Eye
- the other 3 membranes line the posterior (back) of the eye
They are all different:
The sclera (outermost membrane)
- rigid, gives the eye its shape
The choroid (middle membrane)
- provides nourishment for the eye
The retina (innermost membrane)
- active nervous membrane = receiver of stimuli

10. Anatomy of the Eye Transparent Substances: Found inside the eye
The lens
Aqueous humour located between the cornea and lens
- a liquid made up of water and minerals
Vitreous humour
- located between the lens and the retina
- jelly like substance
The eye is the organ of sight, a nearly spherical hollow globe filled with fluids (humors). The outer layer or tunic (sclera, or white, and cornea) is fibrous and protective. The middle tunic layer (choroid, ciliary body and the iris) is vascular. The innermost layer (the retina) is nervous or sensory. The fluids in the eye are divided by the lens into the vitreous humor (behind the lens) and the aqueous humor (in front of the lens). The lens itself is flexible and suspended by ligaments which allow it to change shape to focus light on the retina, which is composed of sensory neurons.

11. What path does light take as it travels through the eye?
1) Light must pass through a number of transparent media before it reaches the nerve cells of the eye. Where are these located?
 On the retina.
2) Label these different structures in the order that light passes through:
vitreous humour, lens, retina, cornea, aqueous humour
1) cornea 
2) aqueous humour 
3) lens 
4) vitreous humour 
5) retina

12. The Path Light Takes in the Eye
Light passes through and is bent by the cornea and then the lens
Images appear inverted on the retina
When looking at near-by objects = the lens curves and thickens
When looking at far object = the lens flattens
The reflex that causes the lens to change shape is called the accommodation reflex
near-far sightedness

13. Flattened lens
thickened lens

14. Light rays enter the eye and focus on the retinal nerve cells (neurons)
These retinal nerve cells then change the light waves that strike them into nerve impulses that are carried along the optic nerve to the visual center of the brain
Optic nerve
Nerve tissue formed by the axons of the retinal cells
Transmits nerve impulses form the retina to the optical centre of the brain
Examples of retinal nerve cells:
Rods = detect light and dark
Cones = detect colour

15. Visual pathway

16. What is the role of the brain in vision?
It is only when the center for vision in the brain (in the occipital lobe) is stimulated that a person has any visual sensation
Therefore, it is not only the eyes alone that allow us to “see” but also the brain.

17. Match the following words with the correct term
Eye
Retina
Optic Nerve
Brain
Transformer
Analyzer
Conductor
Receiver

18. The Chain Reaction Involved in Vision

19. Recall the blindspot?

20. Lenses Convex lenses Concave lenses Also called converging
Cause light to converge on a focal point
This is like the actual lens inside your eye
Concave lenses
Also called diverging lens
Cause light to diverge from a focal point

21. Eye Disorders Hyperopia (far-sighted): Myopia (near-sighted):
The image is focused behind the retina
Close objects are blurred
Requires CONVEX lenses
Myopia (near-sighted):
The image is focused in front of the retina
Distant objects are blurred
Requires CONCAVE lenses
Presbyopia :
loss of elasticity of the lens (usually in old age)
Long eyeball
Myopia
Short eyeball
Hyperopia
-Normal vision occurs when light is focused directly on the retina rather than in front or behind it. A person with normal vision can see objects clearly near and faraway.
-Nearsightedness results in blurred vision when the visual image is focused in front of the retina, rather than directly on it. It occurs when the physical length of the eye is greater than the optical length. For this reason, nearsightedness often develops in the rapidly growing school-aged child or teenager, and progresses during the growth years, requiring frequent changes in glasses or contact lenses. A nearsighted person sees near objects clearly, while objects in the distance are blurred.
-Farsightedness is the result of the visual image being focused behind the retina rather than directly on it. It may be caused by the eyeball being too small or the focusing power being too weak. Farsightedness is often present from birth, but children can often tolerate moderate amounts without difficulty and most outgrow the condition. A farsighted person sees faraway objects clearly, while objects that are near are blurred.

22. Common visual defects

23. Normal View
Myopia
Hyperopia
Near Sighted
Far Sighted

24. OPTICAL ILLUSIONS

25. Your brain has learned certain tricks throughout your life
Your brain has learned certain tricks throughout your life. These are “shortcuts” or easier ways to analyze stimuli.
It is possible to use these shortcuts to trick your brain.
TED Talk

27. Which line is longer?

29. Are these lines bent, or straight?

30. Which man is bigger?

31. What about these doors?

32. Also, your brain has learned that things can only be one thing…
When something which can be seen as two different things appears out of context, your brain will switch from seeing one, to the other… but not both at the same time.

36. Your brain fills in certain missing information that is absent because of your blind spot.
Sometimes it fills in the wrong information

46. What`s wrong?

48. Read this fast…
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50. Cataract Surgery Video Online
Lasik eye surgery animation
You tube:

51. FYI: Nocturnal vision (tapetum)

52. Nocturnal Vision

53. Visual Acuity Tests & Snellen Chart
Visual acuity (vision) is determined in each eye using the Snellen Chart.
The letters for normal vision (20/20) are 3/8-inch tall, viewed at 20 feet.
People with normal vision can read these letters.
A refraction test may also be performed where the doctor puts several lenses in front of the eyes to determine if glasses are needed.
Visual acuity (vision) is determined in each eye using the Snellen Chart. This chart consists of random letters of different sizes. The letters for normal vision (20/20) are 3/8-inch tall, viewed at 20 feet. People with normal vision can read these letters. A refraction test may also be performed where the doctor puts several lenses in front of the eyes to determine if glasses are needed.
To Test Visual Acuity
Position the patient 20 feet in front of the Snellen eye chart Have the patient cover one eye at a time with a card.
Ask the patient to read progressively smaller letters until they can go no further.
Record the smallest line the patient read successfully (20/20, 20/30, etc.)
Repeat with the other eye.

54. Snellen Chart
When checking visual acuity, one eye is covered at a time and the vision of each eye is recorded separately, as well as both eyes together.
In the Snellen fraction 20/20:
the first number represents the test distance, 20 feet.
The second number represents the distance that the average eye can see
If a person sees 20/40, at 20 feet from the chart that person can read letters that a person with 20/20 vision could read from 40 feet away.