the plan… 1 may 2013 (c) mcgraw hill ryerson 2007 start unit 6 – human vision 6.1 human vision ...
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The Plan… 1 May 2013
(c) McGraw Hill Ryerson 2007
Start Unit 6 – Human Vision 6.1 Human Vision PowerPoint Presentation & Worksheet
This is homework…Reading Checks P. 205 & 210
Will check tomorrow…Title Page (including ‘investigative’ questions) due
Friday…Tomorrow: We have two activities to do, so please
don’t dilly dally to class…Tests are marked… 68% class average to this point
More on that later…
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6.1 Human Vision
(c) McGraw Hill Ryerson 2007
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 [SKLER-uh] is the
white part of the eye surrounding the iris.
See pages 202 - 203
Parts of the Eye
Pupil
Iris
Sclera
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6.1 Human Vision
(c) McGraw Hill Ryerson 2007
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.
See pages 202 - 203
Parts of the Eyea
b
c
d
Locate the cornea, optic nerve, lens, and retina.
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The Cornea-Lens-Retina System
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Light rays first entering the eye are refracted by the cornea so that they converge toward the retina.
Light then passes through the lens which “fine-tunes” the focus.
The image that forms on the retina is inverted.
The area where the optic nerve enters the retina is called the blind spot. This area has no light-sensing cells.
See pages 204 - 205
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Black-and-White Visionand Colour Vision
(c) McGraw Hill Ryerson 2007
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.
See page 206
cone
rod
Electron micrograph of the
retina.
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Work Time
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Ok. That’s enough for now… Start worksheet 6.1, ONLY do pages 88 & 89 In 10 minutes we will continue…
Finish early, try Activity 5.1 P 202
Correcting Focus Problems
(c) McGraw Hill Ryerson 2007
Near-sighted visionCan 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 208 - 209
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Correcting Focus Problems
(c) McGraw Hill Ryerson 2007
Far-sighted visionCan 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 208 - 209
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Correcting Focus Problems
(c) McGraw Hill Ryerson 2007
AstigmatismBlurred vision due to a
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 208 - 209
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Blindness
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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.
See page 209
Normal vision
Tunnel vision
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Other Types of Blindness
(c) McGraw Hill Ryerson 2007
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.
See page 210
A test for red-green colour vision deficiency.
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Your Tasks
(c) McGraw Hill Ryerson 2007
Finish 6.1 Worksheet We will review tomorrow
Finish Reading Checks P. 205 & 210 Due tomorrow
Tie up lose ends… Missed assignments Title Page etc
Some of you are writing test today @ lunch… Now you may see you Ch 5 Test Marks
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