Structure, Functions and disorders of the Eye
Session 12: Structure, Functions and disorders of the Eye
Total Session Time: 120 minutes
Students Learning Tasks
By the end of this session students are expected to be able to:
Resources Needed:
SESSION OVERVIEW
|Step |Time |Activity/ |Content |
| | |Method | |
|1 |05 minutes |Presentation |Introduction, Learning Tasks |
|2 |05minutes |Presentation |Definition of the Eye |
| | |Buzzing | |
|3 |50minutes |Presentation |Structure and Functions of the Eye |
| | |Small group | |
| | |discussion | |
|4 |50minutes |Presentation |Common disorders of the Eye |
|5 |05 minutes |Presentation |Key Points |
|6 |05 minutes |Presentation |Evaluation |
SESSION CONTENTS
STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)
READ or ASK students to read the learning tasks and clarify
STEP 2: Definition of the Eye (10minutes)
|Activity: Buzzing (5 minutes) |
| |
|ASK students to pair up and buzz on the following question for 2 |
|minutes |
| |
|What is the eye? |
| |
|ALLOW few pairs to respond and let other pairs to add on points not |
|mentioned |
| |
|WRITE their response on the flip chart/board |
| |
|CLARIFY and SUMMARIZE by using the content below |
o Is situated in the cavity of the orbit the wall which protect it from
injury
o The following are the accessory structures of the eyeball:
STEP 3: Structure and Functions of the Eye (50minutes)
|Activity: Small Group Discussion ( 20 minutes) |
| |
|DIVIDE students into small manageable groups |
| |
|ASK students to discuss on the following question |
| |
|What are the Structure and Functions of the Eye? |
| |
|ALLOW students to discuss for 10 minutes |
| |
|ALLOW few groups to present and the rest to add points not mentioned |
| |
|CLARIFY and SUMMARIZE by using the contents below |
Structure and functions of the eye:
o Regulates the amount of light that enters your eye
o It forms the coloured, visible part of your eye in front of the lens.
o Light enters through a central opening called the pupil.
o The circular opening in the centre of the iris through which light
passes into the lens of the eye
o The iris controls widening and narrowing (dilation and constriction)
of the pupil
o Contains no blood vessels and is extremely sensitive to pain
o A transparent structure situated behind your pupil
o It is enclosed in a thin transparent capsule and helps to refract
incoming light and focus it onto the retina
o A cataract is when the lens becomes cloudy,
o The middle layer of the eye between the retina and the sclera
o It also contains a pigment that absorbs excess light so preventing
blurring of vision
o The part of the eye that connects the choroid to the iris
o A light sensitive layer that lines the interior of the eye
o It is composed of light sensitive cells known as rods and cones
o The human eye contains about 125 million rods, which are necessary for
seeing in dim light
o Cones, on the other hand, function best in bright light
o There are between 6 and 7 million cones in the eye and they are
essential for receiving a sharp accurate image and for distinguishing
colours
o The retina works much in the same way as film in a camera.
o A yellow spot on the retina at the back of the eye which surrounds the
fovea.
o Forms a small indentation at the centre of the macula and is the area
with the greatest concentration of cone cells
o When the eye is directed at an object, the part of the image that is
focused on the fovea is the image most accurately registered by the
brain
o The visible (when the eye is examined) portion of the optic nerve,
also found on the retina
o The optic disc identifies the start of the optic nerve where messages
from cone and rod cells leave the eye via nerve fibres to the optic
centre of the brain. This area is also known as the 'blind spot’.
o Leaves the eye at the optic disc and transfers all the visual
information to the brain.
o The white part of the eye, a tough covering with which the cornea
forms the external protective coat of the eye.
o Are one of the two types of light-sensitive cells in the retina of the
eye
o There are about 125 million rods, which are necessary for seeing in
dim light.
o Are the second type of light sensitive cells in the retina of the eye
o The human retina contains between six and seven million cones
o They function best in bright light and are essential for acute vision
(receiving a sharp accurate image)
o It is thought that there are three types of cones, each sensitive to
the wavelength of a different primary colour – red, green or blue
o Other colours are seen as combinations of these primary colours
[pic]
Figure 12.1:
Structure of the eye
STEP 4: Common Disorders of the Eye (50 minutes)
The common disorders of the eye are grouped into:
Age-related Macular Degeneration (AMD)
o A chronic degenerative condition that affects the central vision.
o Progression of the condition is likely
o Ten per cent of people with macular degeneration have the “wet form”
which may respond to treatment
o The majority of people have the “dry form”
o Two out of three people will be affected by AMD in their lifetime.
Cataract
o A cataract is the clouding of the lens inside the eye.
o With a cataract, light is scattered as it enters the eye, causing blurred
vision
o the population over the age of 55 has a cataract
o Long term use of corticosteroids can increase risk of cataracts
o Exposure to UV light can also increase the risk
o Ageing, smoking and having diabetes can increase the risk of developing
cataract
Diabetic retinopathy
o This condition is a complication of diabetes
o It affects the small blood vessels of the retina
o Blood vessels begin to leak and bleed inside the eye
Glaucoma
o It is a disease that affects the optic nerve at the back of the eye
o Relieving pressure on the nerve reduces progression of the disease
o Early detection and treatment can slow the vision loss
Refractive error
o Refractive error is a focusing disorder of the eye
o Most common cause of vision impairment
o Is associated with ageing the age of 40 years, 22 per cent of the
population has refractive error
o It is correctable by wearing glasses or contact lenses or refractive
laser surgery (selected cases)
STEP 4: Key Points (5minutes)
injury
o Age-related Macular Degeneration (AMD) – 10 per cent
o Cataract – 15 per cent
o Diabetic retinopathy – 2 per cent
o Glaucoma – 5 per cent
o Under-corrected or uncorrected refractive error – 59 per cent
STEP 6: Evaluation (05 minutes)
References
Seeley, R. R., Stephens, T. D., &Tate, P. (2003). Anatomy and Physiology.
New York:
McGraw-Hill.
Shier, A., Butler, J., & Lewis, R. (2004). Hole’s Human Anatomy &
Physiology. New York:
McGraw-Hill.
Standring, S. (2008). Grays’s Anatomy The anatomical basis of clinical
practice. United
Kingdom: Churchill Livingstone Elservier.
Thibodeau, G. A., & Patton, K. T. (1999). Anatomy & Physiology. Saint
Louis: Mosby, Von
Hoffman Press, Inc.
Waugh, A., & Grant, A. (2006). Ross and Willson Anatomy and physiology in
Health and
illness. United Kingdom: Churchill Livingstone Elservier.
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