Ch.10.2 Flashcards
Sight is the ________________ ________________ ________________ for most people. About _________% of the ________________ we receive from the ________________ comes from our eyes. Eyes detect ________________ and help us ________________.
most important sense, 80, information, environment, light, see
When we look at our eyes in the mirror, we can see the ________________, ________________ and ________________. These have ________________ ________________. We can also see the ________________ and the ________________.
eyebrows, eyelids, eyelashes, protective functions, iris, pupil
What is the function of the eyebrow?
—It prevents sweat from getting into the eyes
What is the function of the eyelid?
—It can close to protect the eyes from dirt and strong light
—It can blink to help moisten the eye surface
What is the function of the eyelash?
—prevents small particles (eg dust) from getting into the eyes
The eye is shaped like a ________________.
ball
About _________% of the eyeball is hidden inside ________________________________________, which ________________ the eyeball.
80, the socket of the skull, protects
The eye is a ________________ ________________ made up of ________________ ________________. Different ________________ have different ________________.
complex organs, many parts, parts, functions
What is the function of the sclera?
—A white, tough surface that protects the eyeball
—Made up of dense, connective tissue
What is the function of the retina?
—It contains light-sensitive cells that detect light and produce signals
What is the blind spot?
—It is the spot where the optic nerve leaves the eyeball
—It contains no light-sensitive cells
What is the function of the optic nerve?
—It transmits signals from light-sensitive cells to the brain
What is the function of the focusing muscle? What happens when the muscles contract?
—It changes the thickness of the lens
—The lens become thicker
What is the function of the cornea? Describe its appearance.
—It lets light pass through
—It helps focus light
—It is transparent
What is the function of the iris?
—It controls the size of the pupil.
What is the function of the pupil? Describe the chamber anterior to the pupil
—It regulates the amount of light entering the eye
—It is filed with aqueous humour
What is the function of the lens? Describe the appearance of the lens.
—It lets light pass through
—It helps focus light
—It is transparent and elastic
What is the function of the jelly-like fluid?
—It helps maintain the shape of the eyeball
—It helps focus light
Are the human eyes the most evolved compared to other living things?
No.
Describe how an image is formed in the eye? 1. 2. 3. 4.
- When we look at an object (eg a candle), the light from the object enters our eyes through the cornea
- The cornea, the lens and the jelly-like fluid help focus (bend) the light onto the retina.
- A sharp and inverted image is formed on the retina. The light-sensitive cells on the retina are stimulated by the light to produce signals.
- The signals are sent to the brain through the optic nerve. The brain then interprets the signals as an upright image. Sight is produced.
Describe the image on the retina.
It is inverted both upside-down and left-to-right.
Humans have ___________________ ___________________. Since there is some distance between our eyes, each eyes sees a __________________________________________________________________. Our brain ___________________ the two images from both eyes into ____________________________. This gives us a ______________________________________ and enables us to _________________________________________________________.
binocular vision, slightly different image from the other, combines, one 3D image, perception of depth, judge distances more accurately
When we look at objects at different ___________________, the lens of the eye plays an ___________________ role in ___________________.
distances, important, focusing
In the human eye, the lens is ___________________. Its ___________________ can be changed by the ____________________________________________________, so that ___________________ from objects at different distances can be ___________________ on the ___________________.
elastic, thickness, focusing muscles surrounding it, light, focused, retina
When we look at a near object, the focusing muscles ___________________ and the lens becomes ___________________ so that ___________________________________________________________________________________________________________________________________________.
contracts, thicker, the light from the near object can be focused onto the retina
When we look at a distant object, the focusing muscles ___________________ and the lens becomes ___________________ so that ___________________________________________________________________________________________________________________________________________.
relax, thinner, the light from the distant object can be focused onto the retina
In a diagram, how do we know does the light come from a distant or a near object?
Parallel light lines indicate that the light comes from a distant object.
On the retina, there are two kinds of light-sensitive cells ___________________ and ___________________.
cone cells, rod cells
Cone cells are sensitive to ________________________________, there are _______________ types of cone cells. Each type is sensitive to _________________________________ — ___________________. Cone cells enable us to ______________________________________, but ______________________________________________________.
bright light, three, one of three colours, red, green and blue, see different colours, but only work well in bright light
In ___________________, only ___________________ are stimulated and _____________________________ to the brain. Therefore, it is difficult to ___________________ ___________________ when it is dark.
dim light, rod cells, send signals, distinguish colours
Our eyes enable us to see, but human eyes have ___________________.
limitations
-
-
too small
too close
too far away
What is the purpose of optical instruments?
They are invented by scientists to help extend our vision.
Give five examples of optical instruments from the largest to smallest power.
- Astronomical telescope
- Electron microscope
- Light microscope
- Binoculars
- Hand lens
Apart from not being to see certain objects, what is the other limitation of human vision?
The blind spot.
Each of our eyes has a ___________________. It is located on _______________________________________________________.
blind spot, the retina where the optic nerve leaves the eyeball
When the image of an object is formed on the blind spot, ____________________________________________________________________________. Therefore, we cannot see the object. Why?
no signals will be sent to the brain; this is because there are no light-sensitive cells on the blind spot
People with short sight (or ________________________________, or ___________________) ______________________________________________________ because _____________________________________________________________________________________________________________________________________.
near-sightedness, myopia, cannot see distant objects clearly, the images of the distant objects are formed in front of the retina
What may be the cause(s) of short sight?
It may be caused by the lens being too thick or the eyeball being too long.
How can short sight be corrected?
By wearing glasses with concave lenses (which are also called diverging lens since it diverges light rays)
People with long sight (or ________________________________, or ___________________) ______________________________________________________ because _____________________________________________________________________________________________________________________________________.
far-sightedness, hyperopia, cannot see near objects clearly, the images of the near objects are formed behind the retina
What may be the cause(s) of long sight?
It may be caused by the lens being too thin or the eyeball being too short, or both.
How can long sight be corrected?
By wearing glasses with convex lenses (which are also called converging lens since it converges light rays)
____________________ is mainly found in the ____________________, caused by ________________________________________________________________________. Its symptoms are similar to those of long sight.
Presbyopia, elderly, the reduction of one’s power of accommodation
Why does astigmatism occur?
It occurs because the cornea or the lens (or both) is unevenly curved.
What happens when you have astigmatism?
The light from an object cannot be focused onto the retina to form a sharp image.
How can you correct astigmatism?
By wearing glasses with lenses that have different curvatures at different points.
Astigmatism affects both one’s sight of ____________________ ____________________ and ____________________ ____________________.
faraway objects, nearby objects
What happens when you get cataract?
The lens in our eyes is normally clear. When you get cataract, it becomes cloudy, and some of the light cannot pass through to reach the retina, resulting in blurred vision.
In severe cases, cataract can ________________________.
lead to blindness
What are the causes of cataract?
—Most cases of cataract occur in old age
—Other factors that may cause cataract: eye injuries, prolonged exposure to sunlight and heredity
How do you treat cataract?
The lens can be replaced with an artificial lens through surgery.
What is the cause of colour-blindness?
It is caused by a defect in one or more types of cone cells thus affecting the person’s ability to distinguish colours.
Colour-blindness is an ____________________ defect, and is more common in _______________ than _______________.
inherited, males, females
How can colour-blindness be corrected?
HAH it can’t
Please name 9 ways to protect our eyes with great care.
- After
- Study
- When
- Wear
- Have
- Wear
- Do
- Do
- Do
- After reading or using the computer for 30 to 40 minutes, rest your eyes by looking at distant objects
- Study in sufficient but not strong light. Keep an appropriate reading distance of about 30cm
- When you are using the computer, the monitor should be placed 50-70cm away from your eyes
- Wear safety goggles whenever there is a risk of hurting your eyes during experiments
- Have regular eye check-ups every year and correct eye defects as soon as possible
- Wear a hat and sunglasses to protect your eyes from strong sunlight
- Do not read or write while bending over the desk
- Do not play mobile games while riding in a moving vehicle
- Do not rub your eyes as this can increase the risk of infection
The function of each main part of the eye is related to its form. Give two examples.
The lens is transparent — it can let light pass through
it is also elastic — the thickness can be changed to focus the light onto the retina
The sclera is tough — it is used to protect the eye
Under different light conditions, the size of the pupil changes to ____________________________________________________________. In bright light, the pupil becomes _________________ to ________________________________________________________________________________. In dim light, the pupil becomes ________________ to ________________________________________________________________________________.
regulate the amount of light entering the eye, smaller, decrease the amount of light entering the eye, larger, increase the amount of light entering the eye
