13.6
Time
60–75 min
Vocabulary
• accommodation
• hyperopia
• positive meniscus
• presbyopia
• myopia
• negative meniscus
• contact lens
Skills
per student:
• pencil
• blank sheet of paper
Assessment Resources
Assessment Rubric 2:
Thinking and
Investigation
Assessment Summary 2:
Thinking and
Investigation
Other Program Resources
Skills Handbook 3. Scientific
Inquiry Skills
Skills Handbook 4. Research
Skills
Science Perspectives 10
website www.nelson.com
/sciencepersectives/10
Related Resources
Gizmos: R ay Tracing
(Lenses)
Kitchen, Clyde. Fact and
Fiction of Healthy Vision.
Praiger Publishing, 2007.
The Human Eye
OVERALL EXPECTATIONS
• demonstrate scientific investigation skills in the four areas of skills
• evaluate the effectiveness of technological devices and procedures designed to
make use of light, and assess their social benefits
• demonstrate an understanding of various characteristics and properties of
light, particularly with respect to reflection in mirrors and reflection and
refraction in lenses
SPECIFIC EXPECTATIONS
Scientific Investigation Skills
• conduct inquiries, controlling some variables, adapting or extending
procedures as required, and using standard equipment and materials safely,
accurately, and effectively, to collect observations and data
• select, organize, and record relevant information on research topics from
various sources, including electronic, print, and/or human sources, using
recommended formats and an accepted form of academic documentation
• draw conclusions based on inquiry results and research findings, and justify
their conclusions
• communicate ideas, plans, procedures, results, and conclusions orally, in
writing, and/or in electronic presentations, using appropriate language and a
variety of formats
Relating Science to Technology, Society, and the Environment
• analyze a technological device or procedure related to human perception of
light, and evaluate its effectiveness
Understanding Basic Concepts
• explain the conditions required for partial reflection/refraction and for total
internal reflection in lenses, and describe the reflection/refraction using
labelled ray diagrams
• describe the characteristics and positions of images formed by converging
lenses, with the aid of ray diagrams
• identify ways in which the properties of mirrors and lenses determine their
use in optical instruments
• identify the factors, in qualitative and quantitative terms, that affect the
refraction of light as it passes from one medium to another
KEY CONCEPTS
Science Perspectives 10
ExamView® Test Bank
• The eye can be treated as a lens, and vision problems can be corrected with other
lenses.
Science Perspectives 10
Teacher eSource SUITE
Upgrade
EVIDENCE OF LEARNING
Science Perspectives 10
website www.nelson.com
/sciencepersectives/10
Look for evidence that students can
• describe the eye and explain how accommodation controls sight in the eye
• understand vision problems such as myopia, hyperopia, and presbyopia
• describe how lenses, such as a positive meniscus, a negative meniscus, or contact
lenses, improve human eyesight
906
Unit E: Light and Geometric Optics
55308_04_ch13_p875-938 pp3.indd 906
NEL
11/20/09 7:01:16 PM
SCIENCE BACKGROUND
The Human Eye
• The size and shape of a human eyeball
is crucial for accurate vision. The
eye must be perfectly proportioned
so the image created by the lens
focuses precisely on the retina. The
eye functions like a point and shoot
camera. The image it produces is real
and inverted, just like a camera. Using
ciliary muscles, the eye instantaneously
adjusts itself for a “close-up” or a
“long shot.”
• Both near-sightedness and farsightedness are problems of focal
distance. The real image that the eye
produces focuses in front of the retina
in a near-sighted person; it focuses
behind the retina in a far-sighted
person. It makes sense then, that a
near-sighted person’s vision can be
corrected by spreading the light out a
little before it reaches the retina using
a diverging lens. The correction for a
far-sighted person is the opposite—a
converging lens brings the focus point
closer so it lands directly on the retina.
• The cornea of the eye is a unique
tissue. It is invisible from the front,
can be seen as a clear bulge from the
side, and has no blood vessels inside. It
receives its nutrition from tears and the
water-like solution that fills the eyeball.
The cornea also plays an important
role in focusing light on the retina in
the back of the eye due to its curved,
lens-like shape, although it cannot
itself focus. However, the shape of the
cornea can be surgically changed. This
reshaping of the cornea is the basis of
▼
lasik surgery, which changes the focal
distance of the eye by changing the
curve of the cornea.
• Normally, the pupil changes size to
become smaller in bright light and
larger in dim light. The iris is the
coloured part of the eye and protects
the eye from being damaged by bright
light. The interior of the iris is black
for everyone; the front part gives the
impression of eye colours because
its irregular surface, when combined
with its black backdrop, gives the
appearance of a colour. Blue eyes
are a white surface laid over a black
backdrop. Brown eyes have varying
levels of pigment, and yellow eyes are
actually a light coating of brown over
black.
• The retina, or back two-thirds of the
eye, has a varying degree of sensitivity
to different kinds of light or colours.
The macula is the area where light is
focused. It is filled with cones, which
are cells that sense colour and objects.
Rod cells in other areas provide night
vision, motion sensation, and peripheral
vision (ability to see to the sides.)
• Vision problems can be caused by
damage to the cornea, which may
occur as a result of bacterial or viral
infection, irritants in the environment,
or abrasion due to physical injury. Other
vision problems result from changes
to the structure of the eye that impact
the way light is focused on the retina;
changes in the shape of the eye or the
lens may cause light to be focused in
front of or behind the retina.
TEACHING NOTES
Engage
• Engage students’ interest by holding up a pair of eyeglasses (belonging to
yourself or a volunteer) and asking, How do these help a person see clearly?
Allow the class to divide into small groups and speculate about how eyeglasses
correct vision. To give students a clue, you might mention that the human
eye functions much like a camera. Tell students that they will learn how the
eye functions—and how eyeglasses correct its failure to function.
NEL
55308_04_ch13_p875-938 pp3.indd 907
Writing Tip
Writing a Critical Analysis
If students agree with
the statement that the
development of the
camera as an optical
instrument was based
on the parts of the
human eye and how
they function, have them
write a short piece to
support their opinion. If
students disagree, have
them write a short piece
to support that opinion.
Remind students to
use the strategies they
encountered in the Focus
on Writing feature at the
beginning of the chapter.
Chapter 13 Lenses and Optical Devices
907
11/20/09 7:01:17 PM
Explore and Explain
• Go over the direct comparisons between the eye and a camera. Create a chart
on the board that lists the parts of each. Refer to Figure 1 on page 572 of
the Student Book and the camera illustration on page 567 in Section 5.6.
The aperture, which corresponds to the iris or pupil, is not shown in the
camera illustration, but explain that the aperture is located behind the lens
in a camera because it only opens to admit light when you want to take a
picture. The eye is always open, until the eyelid covers it or the iris restricts
the opening.
• Have students complete Try This: Discover Your Blind Spot. Students will
learn about their blind spot and why it does not normally affect their vision.
T RY THIS
DISCOVER YOUR BLIND SPOT
Skills
• Performing, Observing, Communicating
Purpose
• To demonstrate how to reveal the blind spot in one
eye where the optic nerve passes through the retina.
Equipment and Materials (per student): pencil,
blank sheet of paper
Notes
• Make sure that students are measuring in
centimetres, not millimetres. Remind students to
hold the paper at arm’s length.
Writing Tip
Writing a Critical Analysis
Have students include
in their critical analysis
of contact lenses any
personal experience they
have with contact lenses
or relate experiences of
friends or family members.
Explain that they can use
these experiences as part
of their analysis, but that
they need other sources
of information for their
writing to be credible.
908
Suggested Answers
A. Sample answer: The image of the dot was being
cast on the blind spot in my left eye.
B. Sample answer: As I brought the paper closer to
my left eye, the image of the dot moved on my
retina and no longer fell on the blind spot.
C. Sample answer: When both of my eyes are open,
one eye sees what falls on the blind spot of the
other eye and vice versa.
• Refer students to Figure 2 on page 573. Ask, Why is the image on the retina
inverted? Students should recognize that, just like a camera, the path of light
passing through the lens causes the bottom of the object viewed to strike the
top of the image on the retina, and vice versa with the top of the object. How
is this upside down image corrected? (The brain interprets the image as flipped.)
• Make sure students understand the diagrams of the eye and how light passes
through the eye and forms an image on the back side of the eye or retina. In
the discussion of accommodation, note that these changes in the shape of the
eye’s parts are the same as the changing positions of lenses, objects, and focal
points students have been studying.
• Continue by discussing each of the vision problems that occurs as a result of
issues with focusing, their causes, and the type of lens that is used to correct
the problem. Ensure that students understand the unique features of each
problem:
– Hyperopia (far-sightedness) occurs when the distance between the lens and
the retina is too small or the cornea–lens combination is too weak. This
problem is corrected with converging lenses (positive meniscus).
– Presbyopia is far-sightedness that is age related due to loss of
accommodation by the lens in the eye. It is corrected with converging lenses.
– Myopia (near-sightedness) occurs when the distance between the lens and
the retina is too large or the cornea–lens combination is too strong. This
problem is corrected with diverging lenses (negative meniscus).
• Review Figures 3 to 7 on pages 574–576 of the Student Book, ensuring that
students understand how the light rays focus in each diagram.
Unit E: Light and Geometric Optics
55308_04_ch13_p875-938 pp3.indd 908
• Have students experiment with moving the paper
faster or slower and in and out.
NEL
11/20/09 7:01:17 PM
• Have students complete Research This: Other Vision Problems. Students
will learn about vision problems other than those discussed in this section
and prepare a visual presentation summarizing their research.
RESEARCH THIS OTHER VISION PROBLEMS
Skills
• Researching, Communicating
Purpose
• To find out more about vision problems other than
those described in the section.
Notes
• Encourage students to describe these diseases not
just in medical or scientific terms but in their own
words. They should express examples of the types of
effects you would suffer if you had these problems.
B. Optometrists can observe the dimmest light a
patient can see straight ahead and off to the side
and also check the patient’s sharpness of vision,
looking for abnormalities. More complicated tests
include measuring the pressure in a patient’s eye
and scanning his or her retina with a laser.
Suggested Answers
C. Cataracts are thought to be linked to long–term
exposure to ultraviolet rays and other forms of
radiation. They may also be linked to diseases such
as diabetes and high blood pressure. Congenital
cataracts can also result from a genetic condition
at birth.
A. Astigmatism may be caused by a lens of the eye
that is tilted or misshapen or a cornea that has a
different curvature in one direction than another (like
a football). Astigmatism can be corrected by laser eye
surgery or by corrective lenses (eyeglasses or contacts).
D. Students’ presentations should include details
about the anatomy of the eye and how each
condition affects the parts of the eye. Specific
details of the treatments should also be included
and related to the anatomy of the eye.
Extend and Assess
• Assess students’ grasp of the section by asking: Suppose that a mistake caused
a camera to be “far-sighted.” What could be done to correct the problem? Allow
students time to discuss the problem. Encourage them to draw diagrams.
Confirm that there are at least three solutions to the problem. First, the
camera lens could be changed so it had a shorter focal distance. A second
solution would be to increase the width of the camera chamber so the
image focuses farther from the aperture. A third solution would be to “put
eyeglasses” on the camera. Obviously, this would not be a very practical
alternative! Repeat this discussion, but with the camera being “near-sighted.”
• Have students complete the Check Your Learning questions on page 577 of
the Student Book.
CHECK
YOUR LEARNING
Suggested Answers
1. Both the human eye and a camera have: (1) a converging lens that casts a real, smaller-than-life, inverted image,
(2) a means for focusing images of objects that lie at different distances and (3) a light-sensitive sensor that
“captures” the image.
2. The eye simply sends nerve signals through the optic nerve to the brain. The brain interprets these signals and
creates the image that we see in our mind.
3. (a) Far-sighted individuals see close objects poorly, whereas near-sighted individuals see distant objects poorly.
(b) A converging lens will correct far-sightedness. A diverging lens will correct near-sightedness.
4. (a) One shape is a positive meniscus and the other is a negative meniscus.
(b) A meniscus is more cosmetically appealing than basic lenses because the lenses
are much thinner than basic lenses.
positive
meniscus
NEL
55308_04_ch13_p875-938 pp3.indd 909
negative
meniscus
Chapter 13 Lenses and Optical Devices
909
11/20/09 7:01:17 PM
5. (a) The condition is presbyopia and it is caused by a loss of elasticity in the lens of the eye as a person gets older.
(b) Presbyopia is a form of far-sightedness and thus can be corrected with a positive (converging) meniscus.
6. No. Starting a fire in this manner requires a lens that concentrates light rays by
converging them, and near-sightedness is corrected with diverging lenses. The
image below shows that a diverging lens like those used in glasses to correct nearsightedness will not concentrate the light, as would be necessary.
DIFFERENTIATED INSTRUCTION
Unit Task B ookmark
Much of this material,
including how multiple
lenses can be used
together, will form
background understanding
for students as they
construct their optical
device. Remind students
to refer to this section
when working on the
Unit Task.
Computer Studies
Connection
Encourage students
to research the role of
computer use in the
development of vision
problems. Suggest that
they look for information
relating vision problems to
the number of hours using
a computer each day or
information on whether
there has been an increase
in the percentage of
people who develop vision
problems as computers have
become more widely used.
910
• All students, particularly visual/spatial learners, will benefit from drawing
diagrams on the board similar to those in Figure 3 on page 574 of the
Student Book to accentuate the shape change of the eye. First draw an object
at a distance that is perfectly focused (the eye on the left below). Ask, How
well is the image focused? How do you know? Students should indicate that the
rays meet exactly on the retina, so the image is focused.
• Next, draw the object as it suddenly moves closer (the eye in the middle).
Ask, If the lens does not change shape (accommodate), where will the image focus?
(behind the retina)
• Finally, draw the eye on the above right. Ask, How did the shape of the lens
change? (It got fatter.) How did this change the location of focus? (The image
now focuses precisely on the retina.
• Assess verbal/linguistic learners’ understanding of the above diagrams by
allowing them to explain the diagrams aloud in their own words.
ENGLISH LANGUAGE LEARNERS
• Medical terminology always presents a problem for those not as familiar
with Greek and Latin roots. The suffixes (hyper-, my-, presby-) have Greek
meanings that can be combined with the base word from Latin (opia:
meaning eye or when combined with a suffix sight.) My- means near. Presbys
means old man or elder or, in this case, “old eyes,” as the condition usually
occurs after age 40 or 50. Hyper- means over or in this case over focused and
beyond the focal point of the back of the eye. Have students try to work out
these meaning changes and combinations on their own to increase their
retention of meaning. Students can also use these words in a sentence that
demonstrates their meanings.
Unit E: Light and Geometric Optics
55308_04_ch13_p875-938 pp3.indd 910
NEL
11/20/09 7:01:18 PM