M2 Science
Eye and Optics
Enduring Understandings
Science
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ESOL
A medium can refract light.
Shape determines how lenses form
images.
The eye is a natural optical tool.
Corrective lenses can improve vision.
Essential Questions
Science
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ESOL
What happens when light strikes an
object?
Why do light rays bend when they
enter a medium at an angle?
What determines the type of images
formed by convex and concave
lenses?
How do humans see objects?
What are the types of lenses used to
correct vision problems?
Content
Science
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ESOL
See below
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M2 Science
Eye and Optics
Indicators
Science
ESOL
Students should be able to:
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Trace the path of light as it travels
through different shaped lenses
Describe how lenses produce images
Understand how the eye forms
images
Identify the lens shapes that correct
vision
Identify parts of the cow/sheep eye
and describe functions
Compare and contrast pinhole camera
and human eye
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M2 Science
Eye and Optics
How Light Travels
Light is a form of energy. It travels:
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In waves,
Through empty space
Very quickly (186,225 miles per second)
In straight lines called rays.
What Happens When Light Hits an Object?
A. Reflection
When light rays hit a smooth, shiny surface such as a mirror, they bounce back. You
see whatever is in front of the surface. This is called reflection.
B. Refraction
Light rays cannot turn corners. But, they can be bent by things in
their path. When a light ray goes through a different substance, such as
glass or water, it changes direction. Then they ray comes out on the
other side and goes straight on. This is called refraction
Summary
When a ray of light hits a shiny surface it is REFLECTED.
When light passes from one transparent material to another it is REFRACTED (bent).
What do Lenses Do?
 Bend light for other uses. Most lenses are made out of glass
 Examples: camera lenses take pictures, eyeglasses help people to see, contact lenses help
people to see, microscope lenses help people see really small things
Types of Lenses:
A. Convex: this makes the light focus to a point
B. Concave: this make the light spread out, like a flood light
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M2 Science
Eye and Optics
The Eye: How Do Your Eyes Turn Light Into What You See?
Your eyeballs are almost round. They have a thin covering called the cornea. The cornea helps
to protect your eyes. The black circle in the middle of each of your eyes is the pupil. The pupil is a hole.
Light goes through the pupil
The colored part of your eye around the pupil is the iris. The iris changes the size of the pupil to
let in the right amount of light. When the light is bright, the iris makes the pupil small. When the light is
dim, it makes the pupil large.
Light enters the pupil and goes through the lens. The lens bends light rays so they hit the retina
at the back of the eye. The retina is attached to the optic nerve. The optic nerve sends messages to
your brain. Your brain sees these messages as pictures.
Label the Eye. Use the words in the vocabulary box.
cornea
iris
pupil
retina
lens
optic nerve
vitreous
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Eye and Optics
How Do Lenses Correct Eyesight/Vision?
This is an “eye chart.” If you have 20/20 vision, it means that at a distance of
20 feet, you can read a certain line on the chart and your vision is normal. (This line is
labeled ‘line 20.’) If you can only see the top line, then your vision is 20/200. That top
line is labeled ‘200.’ This means that you can see at 20 feet, what most people can see
from 200 feet.
What happens if your vision is not “perfect?” Vision depends on the shape of your
eyeballs. The shape of your eyeballs determines where the light rays land. If your
vision is not perfect, you will need to get glasses. Let’s look at two types of imperfect
vision:
I. Fuzzy – Myopic – Nearsighted Vision
If you have difficulties see things far away from you, then your are myopic, or nearsighted. The
light enters your eye, BUT doesn’t reach the retina. You have a slightly longer eyeball. People need a
concave lens to “fix” this. (Remember that this makes the light spread out more.) The light will now
reach the retina.
II. Fuzzy – Hyperopic – Farsighted Vision
If you have difficulties seeing things close to you, e.g. when reading books, cereal boxes, etc.
then you are hyperopic, or farsighted. The light enters your eye, AND goes behind the retina. You have
a slightly shorter eyeball. People need a convex lens to fix this. (Remember that this makes the light
focus into a point.) The light now reachs just the front of the retina.
The Eye and What Type of Lenses are Needed to Correct Its Vision
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Eye and Optics
Determine if the Eyeball is “Normal,” Myopic, or Hyperopic. Explain why.
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M2 Science
Eye and Optics
Lenses
You know that light can be refracted or bent. Lenses are used for bending light. They can make
objects look small or larger. They can make things that are far away look close. How do lenses work?
Lenses are made of glass or other materials that light can pass through. The two main kinds of
lenses are concave lenses and convex lenses. A concave lens is thinner in the middle than it is at the
edges. A concave lends bends light rays so that they spread apart. A convex lens is thicker in the middle
than it is at the edges. A convex lens bends light rays so that they come together.
Compare concave and convex lenses. Put this information in a chart.
Concave Lenses
Convex Lenses
Lenses have many different uses. People who have trouble seeing wear eyeglasses or contact
lenses. Eyeglasses are lenses worn in front of the eyes. Contact lenses are lenses worn on the eye.
Contact lenses are made of plastic. Concave lenses help people who have trouble seeing objects in the
distance. Convex lenses help people who have trouble seeing objects close to them.
Scientists use lenses in microscopes. The lenses in microscopes make very tiny objects look
larger. Scientists use microscopes to study things that are normally too small to see. Scientists also use
lenses in telescopes. Telescopes make faraway objects look as if they are closer. Scientists use
telescopes to study stars and planets.
Lenses are used in cameras. They focus light on the film. Without lenses, there would not be
photographs or movies.
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M2 Science
Eye and Optics
Turn the following into questions. The question must be one that would give an answer like the ones
below.
1. Our eyes have over 2,000,000 working parts!
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2. A blink of an eye takes 1/10 of a second.
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3. An average person blinks approximately 17,000 times per day.
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Our eyelashes help keep airborne particles and sweat from entering our eyes.
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An adult’s eyeball is actually the approximate size of a golf ball!
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Match the vocabulary with the definition
Cornea
The colored part of the eye that is a ring of muscles that control how
much light is passed in to the eye. It contracts to limit light intake and
expands to allow more light intake. A pigment called melanin gives it its
color
iris
The white protective area that covers most of the eye
lens
A light-sensitive membrane that lines the inner eyeball and is connected
to the brain via the optic nerve
pupil
A thin covering that protects the eye
retina
Lies just behind the pupil and is the area that focuses light that enters the
eye
sclera
The opening in the center of the iris, which protects the inside of the eye.
It changes depending on the amount of light. In low light, it relaxes
allowing more light. In bright light the muscles contract to allow less light
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Eye and Optics
Iris –
Pupil – the opening in the center of the iris that changes depending on the amount of light to protect
the inside of the eye. In low light the pupil relaxes allowing more light. In bright light the muscles
contract to allow less light
Lens –Retina –
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M2 Science
Eye and Optics
Normal eyesight is present when light rays strike the retina, causing a clear image to form
In myopia (nearsightedness), rays of light focus in front of the retina instead of upon it, causing distant
objects to appear blurred www.wangvisioninstitute.com/book/chap-02.html
In hyperopia (farsightedness), rays of light focus behind the retina.
A camera has a convex lens. It focuses light on an electronic imaging sensor or a photographic
film.
The image on the sensor or film is upside down. The camera turns the image the right way up on the
viewing screen or in the viewfinder.
Lenses are used to correct eyesight when, because of the shape of the eye, the light doesn't focus
exactly on the retina.
People who are near sighted have a slightly longer eyeball, so the light focuses just in front of the
retina. A concave lens makes the light focus further back so it focuses exactly on the retina and the
person sees a sharp image.
People who are far sighted have a slightly shorter eyeball, so the light focuses just behind the retina. A
convex lens make the light focus further forwards so it focuses exactly on the retina and the person sees
a sharp image.
Fiber optics involves sending light down thin transparent flexible plastic or glass fibers. A fiber optics
cable consists of many separate fibers.
Light travels in straight lines inside an optical fiber by reflecting off the internal walls of the fiber.
Telephone messages can be carried by light in a fiber optics cable. Digital messages consist of ones
(light on) and zeros (light off). Special electronic devices turn the sequence of ones and zeros into
sound. CD players also work by turning light, reflected from the surface of the CD as a sequence of ones
and zeros, into sound.
Pictures: www.hobbyprojects.com/general_theory/light.html
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M2 Science
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Eye and Optics
Light is given off in tiny particles called photons. Photons have no mass. They are not matter.
Photons travel in waves. Most light waves have so many photons that the separate photons
cannot be seen. They look like solid waves of light.
Sound waves of movements of the matter through which they travel. So, wound waves can
travel only through matter. But light waves are waves of photons. So light waves can travel through
empty space.
Light travels very quickly. It goes through 186,225 miles ( kilometers) of air in 1 second. Light
travels much faster than sound. Sound goes only about one fifth of a mile in a second. If you have been
in a thunderstorm, you probably saw the lightning before you heard the thunder. The light from the
lightning reached you more quickly than the sound did.
Light travels in straight lines called rays.
Long sight. The eye really is too short; the light rays do not meet before striking the retina
The rays of light (A) enter the eye, and are focussed on the retina by the lens
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M2 Science
Eye and Optics
Short sight. In this case the eye is too long from front to back, or the lens is too curved ways read in
sufficient light so that it falls upon the work from above and behind. The eyes should never be used at
twilight. Flickering gas-jets and lamps are extremely injurious to the eyes. If the eyes are tro uble-some, it
is best to use them only in daylight.
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M2 Science
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Eye and Optics
Explain that our eye is much more complex then the visual part, or front, of our eye that we see
when we look in a mirror.
Explain to students the various parts of the eye, using worksheet 1a:
o Iris – the colored part of the eye that is a ring of muscles that control how much light is
passed in to the eye. It contracts to limit light intake and expands to allow more light
intake. A pigment called melanin gives the iris its color
o Pupil – the opening in the center of the iris that changes depending on the amount of
light to protect the inside of the eye. In low light the pupil relaxes allowing more light.
In bright light the muscles contract to allow less light
o Lens – lies just behind the pupil and is the area that focuses light that enters the eye
o Sclera – the white protective area that covers most of the eye
o Retina – a light-sensitive membrane that lines the inner eyeball and is connected to the
brain via the optic nerve
Explain how the eye works:
o Light passes through the cornea and the pupil and is then focused by the lens into the
vitreous humor and is projected onto the retina. The retina is like the film in a camera
that captures the images.
o Light sensitive receptor cells convert the light into messages that are sent to the brain
via the optic nerve.
o The eye is similar to the camera in how it works. With our eyes, light passes through the
lens and cornea and bends or refracts. When it refracts the image turns upside down
and backward onto the retina. With a camera light enters the lens and turns upside
down and backward onto the film.
Definitions of Parts of the eye
Cornea - the clear, dome-shaped tissue covering the front of the eye.
Iris - the colored part of the eye - it controls the amount of light that enters the eye by changing the size
of the pupil
Lens - a crystalline structure located just behind the iris - it focuses light onto the retina
Optic nerve - the nerve that transmits electrical impulses from the retina to the brain
Pupil - the opening in the center of the iris- it changes size as the amount of light changes (the more
light, the smaller the hole)
Retina - sensory tissue that lines the back of the eye. It contains millions of photoreceptors (rods and
cones) that convert light rays into electrical impulses that are relayed to the brain via the optic nerve
Vitreous - a thick, transparent liquid that fills the center of the eye - it is mostly water and gives the eye
its form and shape (also called the vitreous humor)
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Eye and Optics
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Eye and Optics
Content From Science Curriculum
Part A
When light passes at an angle from one medium (e.g. air) into a different medium (e.g.
water or glass) it is bent. This is why people's legs look shorter when they are standing in
a swimming pool.
Lenses are designed to bend light in useful ways. Most lenses are made of glass.
A convex lens focuses light to a point. A concave lens makes the light spread out.
A camera has a convex lens. It focuses light on an electronic imaging sensor or a
photographic film.
The image on the sensor or film is upside down. The camera turns the image the right way
up on the viewing screen or in the viewfinder.
Lenses are used to correct eyesight when, because of the shape of the eye, the light
doesn't focus exactly on the retina.
People who are near sighted have a slightly longer eyeball, so the light focuses just in
front of the retina. A concave lens makes the light focus further back so it focuses exactly
on the retina and the person sees a sharp image.
People who are far sighted have a slightly shorter eyeball, so the light focuses just
behind the retina. A convex lens make the light focus further forwards so it focuses
exactly on the retina and the person sees a sharp image.
Fiber optics involves sending light down thin transparent flexible plastic or glass fibers. A
fiber optics cable consists of many separate fibers.
Light travels in straight lines inside an optical fiber by reflecting off the internal walls of
the fiber.
Telephone messages can be carried by light in a fiber optics cable. Digital messages
consist of ones (light on) and zeros (light off). Special electronic devices turn the
sequence of ones and zeros into sound. CD players also work by turning light, reflected
from the surface of the CD as a sequence of ones and zeros, into sound.
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Eye and Optics
Part B - The Eye
The parts of the eye are cornea, sclera, pupil, iris, lens, retina and optic nerve.
The cornea is the transparent front surface of the eye.
The sclera is the white of the eye.
The pupil is the hole in the iris through which light passes on its way to the retina.
The iris can change the size of the pupil. It regulates the amount of light entering the
eye.
The lens focuses light on the retina.
The lens is convex. It can change shape so you can focus light onto the retina from
objects at different distances.
The retina senses the light.
The image on the retina is upside down.
The optic nerve is a bundle of neurons that carry messages from the retina to the brain.
The brain turns the image the right way up.
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