Senior Science
Preliminary Course
8.4 Humans at Work
Section 3
Protecting
The Eyes
Section 3 ::: Protecting the eyes
8.4.3.a / Outline the function and structure of the eye including the: conjunctiva, cornea, sclera, retina including rods and cones, tear ducts, eyelid, convex lens, muscles moving the eyeball
8.4.3.b / Identity that the eye produces tears as a protective mechanism
8.4.3.c / Assess the need for eye exercises in many work situations
8.4.3.d / Explain first aid procedures when substances are splashed into the eye
8.4.3.e / Discuss why light emitted naturally or by some technological devices, including: solar eclipse, welding light, laser light, high intensity white light may be cause for concern
8.4.3.f / Outline the structure and discuss how the composition of one type of specialized protective glasses is designed to protect the eye and sight such as: welding goggles, polarized sunglasses, safety goggles in the laboratory, glasses that protect against UV light
8.4.3.g / Describe safety regulations involving maintenance of safety glasses
8.4.3 i. / Gather, process and analyze information from secondary sources to present information on how vision is affected by deformation or damage to the surface of the eye including sport injuries
8.4.3 ii / Process information from secondary sources and use available evidence to outline how increases in scientific understanding have impacted on the development of one protective eyewear such as: welding goggles, polarized sunglasses, safety goggles in the laboratory, glasses that protect against UV light
8.4.3.a / Outline the function and structure of the eye including: conjunctiva, cornea, sclera, retina including rods and cones, tear ducts, eyelid, convex lens, muscles moving the eyeball
The Eye – Function & Structure
What to do
Read the passage below and answer the questions that follow.
The eyelids and eyelashes protect the front of the eyeball. They prevent particles from falling on the surface of the eye. The eyelids also spread mucus and tears over the eyeball. If something touches the eye, the lids blink in a protective reflex action. The conjunctiva is a protective film that covers the cornea. Protection is also provided by `tears’, which wash over the front of the eye. Small muscles attached to the back of the eyeball move the eye around in its socket.The eyeball is a fluid filled sphere approximately 2.5 cm in diameter. The outer wall consists of three layers. The outer layer is the sclera, the protective container in which the eye is located. Part of the sclera is the ‘white’ of the eye. The front section of the sclera is the transparent cornea. The middle layer is the dark choroid. It has many blood vessels that nourish the retina. The front part of this layer (seen through the cornea) is the coloured iris. The pupil is the opening at the center of the iris, and it regulates the amount of light entering the eye. The retina makes up the inner layer of the wall of the eye. The retina is made up of two light-sensitive cells – rods and cones. Nerves from the retina join the optic nerve and carry messages from the eyes to the brain.
The lens lies behind the iris. A ring like muscle, called the ciliary muscle, can change the shape of the lens. Light is focused onto the retina by the lens. The space between the lens and cornea is filled with aqueous humour. Behind the lens is a jelly like vitreous humour. These liquids help the eye to hold its shape, while the lens enables us to focus our vision.
Notes Questions
1. Decide if the following statements are TRUE or FALSE,
a. Tears are the most important protective feature of the eye.
b. The outer wall of the eyeball contains three layers.
c. Rod and cone cells are light sensitive and part of the retina.
d. The function of the lens is to focus light onto the optic nerve.
e. Light enters the eye through an opening in the iris.
f. The cornea protects the conjunctiva.
g. The vitreous humour is a liquid.
h. The choroid extends at the front of the eye to become the cornea.
j. The correct order of the layers of the eyeball is retina, choroid and sclera.
k. The iris can change shape due to ciliary muscles.
2. The 10 mixed up sentences in the table below contain some of the information from the passage. Use the information from the passage to rewrite these sentences so that each corrected sentence contains one phrase from each of columns A, B, C and D.
COLUMN A /COLUMN B
/ COLUMN C / COLUMN Da.
b.
c.
d.
e.
f.
g.
h.
i.
j. / The eye is
The conjunctiva
The white part
A jelly like
The optic nerve
The iris
The pupil
The retina
Light is
The eyelids / A hollow sphere
Of the eye
Carries messages
Regulate the
Focussed onto
Is a protective
Liquid
Is coloured
Is made up of
Spread / With the pupil
Filled
Amount of light
Film covering
Mucus & tears
Is part of
The retina
Filling the eye
Light sensitive
From the eyes / Rod & cone cells
Over the eye
With liquid
Is vitreous humour
At its centre
To the brain
By the lens
The sclera
Entering the eye
The cornea
3. Trace this diagram into your book, and then use the information in the passage to label all the parts indicated.
4. Construct a table that shows the different parts of the eye and their functions.
a. Include all the parts of the eye listed below.
b. Use some or all the information about functions written below.
c. Some information will need to be researched.
Conjunctiva Choroid Cornea Eyelashes
Eyelids Iris Convex lens Optic nerve
Retina (rods & cones) Sclera Tears ducts Muscles in eye
The light sensitive area of the eye
The part that changed shape to focus for near or distant objects.
The part controlling the amount of light entering the eye.
They keep things like dust out of the eye.
They lubricate and wash the front of the eye.
They protect the eye from too much light or injury.
Tough white protective outer layer
8.4.3.b / Identity that the eye produces tears as a protective mechanismProtecting the Eyes: Tears
Reading focus – Tears as a protective mechanism
Composition of tears
The cornea and conjunctiva are constantly exposed to the external environment – changes in humidity and temperature as well as air pollutants can affect the eyes. Our tears represent the eye’s first protective barrier, providing some protection from changes in the environment. In some people this natural barrier is disrupted causing discomfort and an increased potential for disease.
[Source: Pamphlet – Alcon Laboratories]
Tears have 4 basic functions:
· to keep the eye’s surface moist and act as a lubricant.
· to form a mirror finish and assist with clear vision.
· to help protect the eye from infections and
· to provide the surface of the eye with vital nutrients to keep the eyes healthy.
Most tears are produced in the lacrimal glands above the inside corner of each eye. Each time a person blinks, a small amount of tear fluid is spread over the eye. The fluid lubricates the eyes and helps clear foreign matter, such as dust and hair, from the eyeball. Tears are salty to balance salt concentration inside and outside the eye. This assists in keeping the eye moist. The lysozyme in tears is an enzyme that fights bacteria. Tears also contain proteins that help make the eye immune to infection.
There are a number of products used to treat various conditions affecting the eye. These products either:
· reinforce the functions of tears (or other parts of the eye) or
· remove substances that build up on the eye
For example artificial tears are used to treat dry eye. It can occur if too few tears are produced or tears produced are of a poor quality. Ideally, an artificial tear solution should duplicate the composition of human tears.
Notes Questions
5. Why does the eye need protection
6. Name two functions of tears involved in protecting the eye.
7. Name the enzyme in tears that helps it fight bacteria.
8.4.3.i / Gather, process and analyze information from secondary sources to present information on how vision is affected by deformation or damage to the surface of the eye including sport injuriesEye injuries
Reading focus - Affect on vision by deformation or damage to the eye surface.
The area around the eye is constructed in such a way as to give the eye the greatest possible protection against external impact. Direct impact against the eye from a large object, eg a football, can result in bleeding and swelling in the eyelid and surrounding soft tissues but seldom injures the eye itself. Blows from small or pointed objects, such as elbows, fingers, sticks, rackets, squash balls and pucks can, on the other hand, cause direct injuries to the eyeball.
A squash ball fits neatly into the eye socket
Corneal abrasions
One of the commonest eye injuries in sport is a small wound on the cornea (that is, the clear central part of the eye that covers the iris). A fingernail, a foreign body in the eye or a contact lens, can cause the wound.The wound can cause pain and a gritty sensation in the eye, especially in bright light and when blinking. This results in a minor problem with vision because people tend to keep the wounded eye closed to reduce pain. Increased tear flow is also a common symptom. This can cause vision to be a little blurry.
If a wound on the cornea is suspected, a doctor should be seen for advice since the injury can affect the sight. The treatment is usually ointment or eye drops and rest, and an eye pad may be applied for a day or so.
What to do
1. Gather information about TWO eye injuries that cause problems with vision.
2. Put the information into a table with the following headings
Ø Description of the injury and what happens to the eye and
Ø How vision is affected.
Notes Questions
8. What sorts of objects could cause a direct injury to the eyeball?
9. What is a corneal abrasion?
8.4.3.c / Assess the need for eye exercises in many work situationsEye Hazards at Work
Office workers of all kinds spend many hours using a variety of keyboard equipment. Keyboard equipment that is properly selected, coordinated and adjusted will help prevent a range of injuries caused by overuse, poor posture and poor lighting. There are a number of eye hazards for office workers that need to be assessed.
Screen placement Set the eye-to-screen distance that allows a relaxed focus on the screen. Usually this will be within an arm’s length. Set the top of the monitor so that the top of the screen is below eye height. The bottom of the screen should be able to be viewed without a marked inclination of the head. Usually this means that the centre of the screen will need to be near shoulder height.
Glare and reflection To determine if there is glare from overhead lights the seated worker should hold an object (eg book) above the eyes at eyebrow level. Then decide if the screen image becomes clearer (in the absence of overhead glare). To detect reflections from the desk surface hold a book above the surface and determine the change in reflected glare from the screen.
To reduce reflections tilt the screen so that reflections are directed below eye level. An anti glare screen can also be used.
Eye Strain and eye exercises for workers
Working with Visual Display Unit’s or other close work can produce tired and sore eyes. To reduce the strain on the eyes some work healthy practices can be useful.
· Look away into the distance every ten minutes or so. This will rest the eyes.
· Alternatively, cover the eyes with the hands without pressing and breathe deeply eight or nine times.
· Make sure screen brightness is down to a comfortable level.
· Use suitable text and background colours – black on white, yellow or white on black. Avoid red, green and yellow on white.
· Reduce reflection and glare
· EYE EXERCISE in work situations: In the work situation eye exercises are only necessary if the person has a predisposition to an eye disorder.
Notes Questions
10. Name three causes of eye injuries associated with the use of keyboards.
11. Name two eye hazards that need to be assessed for office workers.
12. Outline how to set up a computer screen at the correct height.
13. Explain how to detect glare from overhead lights.
14. Identify two ways to reduce glare on computer screens.
15. Outline two work healthy practices used to reduce eye strain
16. Who should do eye exercises in work situations?
Workstation set-up for a keyboard operator.Source – Workcover pamphlet
What to do
Read and answer the following question
Assess the need for eye exercises in many work situations
The question provides no structure, yet it requires an extended answer. In order to answer the question a plan needs to be developed. The steps below show one way of developing a plan.
Step 1 Underline and recall meanings of the important words in the question
Eye exercises; work
Step 2 Circle the KEY (Board of Studies) verb in the question and recall the meaning of the verb(s). Assess – make a judgment of.
Step 3 [NB this step may require some research]
§ Outline the nature of the risk (work situations involving eye hazards).