1. The iris is the coloured circle of muscle surrounding the pupil.
6.1 Human Vision
Parts of the Eye
The pupil is the dark transparent region in the centre of the eye where light enters.
The iris is the coloured circle of muscle surrounding the pupil.
The iris controls the amount of light entering the eye.
The sclera is the white part of the eye surrounding the iris.
See pages
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2. Cornea-Lens-Retina Systemb
The cornea is the transparent tissue covering the iris and the pupil.
Behind the pupil is a flexible convex lens.
The lens focuses light onto the retina located in back of the eye.
The retina is covered with light sensitive cells that convert light energy into electrical energy.
Electrical signals are sent to the brain by the optic nerve. a c d
Locate the cornea, optic nerve, lens, and retina.
See pages
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3. Not in your notes
Aqueous Humour - Fluid between the lens and cornea, supports cornea and lens, provides nutrients to cornea (cornea has no blood vessels).
Vitreous Humour - Fluid behind lens, supports lens and gives shape to eye
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4. The Cornea-Lens-Retina System
Light rays first entering the eye are refracted by the cornea so that they converge toward the retina.
Cornea actually does most of the focussing.
Locate your blind spot: see page 205
See pages
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5. The Cornea-Lens-Retina System
Light passes through the lens which “fine-tunes” the focus.
The lens does the remaining of the focussing by changing shape.
Muscles attached to the lens contract, causing lens to be thicker. A thicker lens can focus on near objects. This is why you may get eye strain from reading.
When looking at a distant object, the muscles relax, increasing tension on the lens, making it thinner.
Locate your blind spot: see page 205
See pages
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6. (c) McGraw Hill Ryerson 2007

7. The Cornea-Lens-Retina System
The image that forms on the retina is inverted.
Locate your blind spot: see page 205
See pages
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8. The Cornea-Lens-Retina System
The area where the optic nerve enters the retina is called the blind spot.
This area has no light-sensing cells.
Locate your blind spot: see page 205
See pages
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9. Locate your blind spot: see page 205
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10. Check your understanding
What happens to light rays after they enter the eye through the pupil?
Where does most of the focussing in the eye occur?
How does the lens change to focus on object that are close?
How does the lens change to focus on object that are distant?
Why is the image of an object inverted when it strikes the retina?
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11. Answer Reading Check p205 – hand in Friday WB p88
Homework
Read pages
Answer Reading Check p205 – hand in Friday
WB p88
Eye parts and function WS – due Friday
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12. Black-and-White Vision and Colour Vision
The retina contains two types of light-sensitive cells called rods and cones.
Rod cells are cylinder-shaped cells that allow us to see images in shades of light and dark when the light is dim.
Cone cells are cone-shaped cells that allow us to see colour in bright light.
rod
cone
Electron micrograph of the retina.
See page 206
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13. Correcting Focus Problems
Near-sighted vision
Can not clearly focus on distant objects.
Occurs because the lens converges the light rays to form an image in front of the retina.
A concave lens is used to correct near-sighted vision.
See pages
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14. Correcting Focus Problems
Far-sighted vision
Can not clearly focus on nearby objects.
Occurs because the lens converges the light rays to form an image behind the retina.
A convex lens is used to correct far-sighted vision.
See pages
(c) McGraw Hill Ryerson 2007

15. Correcting Focus Problems
Astigmatism
Blurred vision due to an irregular shaped cornea.
Causes the image to focus on more than one point on the retina.
Corrected by using eyeglasses, contact lenses, or laser surgery.
See pages
(c) McGraw Hill Ryerson 2007

16. Most people who are legally blind can perceive some light.
Blindness
Blindness is any vision impairment that keeps people from carrying out important life functions.
Most people who are legally blind can perceive some light.
May be able to see a tiny part of the middle of the whole scene (tunnel vision).
May be able to only see the edges but not directly ahead.
May be able to see light and dark but not clearly, even with visual aids.
Normal vision
Tunnel vision
See page 209
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17. Other Types of Blindness
Snow blindness is a temporary blindness caused by overexposure to the glare of sunlight.
Night blindness is a condition in which it is difficult to see in dim light.
Colour blindness is the ability to see only in shades of grey.
Colour vision deficiency is the inability to distinguish certain colours.
The most common is the inability to distinguish between red and green.
A test for red-green colour vision deficiency.
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18. Homework
Read pages Reading Check p210 #1-6 Rods and Cones WS – due Thurs, May 17. Read Eye Dissection – Next Class
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