Lesson 3
Eye Care
Our eyes work in a way that is similar to a camera.
Like the click of a camera lens, in the blink of an eye images
are formed in the process of vision.
Lesson 3
Lesson Objectives
In this lesson, you’ll learn to:
Identify the parts of the eye.
Understand how the eye forms visual images.
Examine the effects of health behaviors on the eye.
Describe different types of eye problems.
Lesson 3
Your Eyes
Structure of the Eye
The eyebrows, eyelashes, and eyelids protect the eyes
from foreign particles and bright light.
Each eye has a group of structures that make and allow
drainage of tears. One of these structures is the
lacrimal gland.
As you blink, tears are moved across the surface of the
eye. Tears keep the surface of the eyeball moist and
clear of foreign particles.
Lesson 3
Parts of the Eye
Optic Nerve and Three Layers of the Eyeball Wall
Lesson 3
Parts of the Eye
The Outer Layer
The outermost layer of the eye
is made up of the sclera and
the cornea.
The sclera is composed of
tough, fibrous tissue that
protects the inner layers of the
eye and supports and shapes
the eyeball.
At the front of the eye is the
cornea.
Lesson 3
Parts of the Eye
The Middle Layer
Within the middle layer of the
eyeball is the choroid and the
iris.
The muscles of the iris control
the size of the pupil.
In bright light the pupil
constricts and in dim light it
enlarges to let in more light.
Lesson 3
Parts of the Eye
The Inner Layer
The light-sensitive cells in the
retina are called rods and cones,
each named for its basic shape.
When light stimulates these cells,
a nerve impulse travels to the
brain via the optic nerve, which
is located at the back of the eye.
Behind the iris and the pupil is
the lens of the eye.
Lesson 3
Vision
The Process of Image Formation
Image formation begins as light passes through the cornea,
pupil, and lens and reaches the retina.
Light rays are first focused by the curved cornea, and then
the focus is refined by the lens.
Muscles attached to the lens contract or relax to change its
shape.
Light stimulates rods and cones in the retina, and a nerve
impulse is transmitted to the brain through the optic nerve.
Lesson 3
Vision
How You View Objects
Click image to view animation.
Lesson 3
Vision
Sharpness of Vision
The sharpness of vision can be measured by reading an eye
chart.
If you have 20/20 vision, you can stand 20 feet away from an
eye chart and read the top eight lines.
If you have 20/60 vision, you can see the chart from 20 feet
the way a person with normal vision would see it from 60 feet.
Reading an eye chart measures only one aspect of vision.
Lesson 3
Healthy Eyes
Ways to Keep Your Eyes Healthy
Follow a well-balanced
diet.
Protect your eyes.
Have regular eye
exams.
Rest your eyes
regularly.
Lesson 3
Eye Problems
Vision Problems
Two common vision problems reflect the inability of the eye to
properly focus light on the retina.
Myopia
Myopia, or
nearsightedness,
results in a person not
being able to see
distant objects clearly.
Hyperopia
Hyperopia, or
farsightedness, results
in a person being able
to see distant objects
clearly, while near
objects appear blurred.
These conditions can be corrected with glasses or contact lenses.
Lesson 3
Eye Problems
Other Vision Problems
Astigmatism: Because of an irregularly curved cornea or
lens, the eye is not able to focus properly, resulting in images
that appear blurry.
Strabismus: If the muscles of the eyes are weak or don’t
function properly, strabismus may result.
Lesson 3
Eye Problems
Diseases of the Eye
Sties: A sty is an inflamed swelling of a sebaceous gland
near the eyelash.
Conjunctivitis or pinkeye: This is an inflammation of the
conjunctiva, a thin membrane that covers the sclera lining of
the eyelids.
Detached Retina: This occurs if a portion of the retina is
separated from the choroid as a result of natural aging or
from an injury. Treatment includes using a laser to repair a
tear or surgery to reattach the retina.
Lesson 3
Eye Problems
Serious Eye Diseases
Glaucoma: In glaucoma, abnormally high pressure inside the
eyeball leads to irreversible damage of the retina and the
optic nerve and can result in loss of sight.
Cataracts: In this condition, the normally transparent lens
becomes cloudy.
Macular Degeneration: This condition occurs when the
light-sensing cells of the macula, the portion of the retina
directly opposite the lens, begin to malfunction.
Lesson 3
Quick Review
Choose the appropriate option.
Q. The retina is the light-sensitive
membrane on which images are
cast by the _________.
1. sclera
2. cornea
3. choroid
4. lacrimal gland
Lesson 3
Quick Review - Answer
A. The retina is the light-sensitive membrane on which images
are cast by the cornea.
Click Next to attempt another question.
Lesson 3
Quick Review
Provide a short answer to the question given below.
Q. List the structures that make up the three layers of the
eyeball wall.
Click Next to view the answer.
Lesson 3
Quick Review - Answer
A. The structures that make up the three layers of the eyeball
wall are as follows:
1.
Outer: Sclera and cornea
2. Middle: Choroid, iris, pupil
3. Inner: Retina
Click Next to attempt another question.
Lesson 3
Quick Review
Provide a short answer to the question given below.
Q. Explain the difference between myopia and hyperopia.
Click Next to view the answer.
Lesson 3
Quick Review - Answer
A. Myopia is nearsightedness—when near objects are clear and
distant objects are blurry.
Hyperopia is farsightedness—when near objects are blurry
and distant objects are clear.
Click Next to attempt another question.
Lesson 3
Quick Review
Analyze the following question.
How might having night blindness affect a person’s activities?
Lesson 3
Quick Review - Answer
A. Correct! The retina is the light-sensitive membrane on which
images are cast by the cornea.
Click Next to attempt another question.
Lesson 3
Quick Review - Answer
You have answered the question incorrectly. Go back to try again,
or click Next to view the correct answer.
Lesson 3
Your Eyes
Structure of the Eye
The eyebrows, eyelashes, and eyelids protect the eyes
from foreign particles and bright light.
Each eye has a group of structures that make and allow
drainage of tears. One of these
structures is the
The lacrimal
lacrimal gland.
gland is the gland
that secretes tears
As you blink, tears are moved across the surface of the
into ducts that
eye. Tears keep the surface of the eyeball moist and
empty into the eye.
clear of foreign particles.
Lesson 3
Parts of the Eye
The Outer Layer
The outermost layer of the eye
is made up of the sclera and
the cornea.
The sclera is composedThe
of sclera
is the
tough,
tough, fibrous tissue
that
of
protects the innerwhite
layerspart
of the
eye and supports the
andeye.
shapes
the eyeball.
At the front of the eye is the
cornea.
Lesson 3
Parts of the Eye
The Outer Layer
The outermost layer of the eye
is made up of the sclera and
the cornea.
The sclera is composed of
cornea
tough, fibrousThe
tissue
thatis
transparent
protects athe
inner layers of the
that
bends
eye and tissue
supports
and
shapes
and focuses light
the eyeball.
before it enters the
At the front
lens.of the eye is the
cornea.
Lesson 3
Parts of the Eye
The Middle Layer
Within the middle layer of the
eyeball is the choroid and the
iris.
The muscles of the
control
Theiris
choroid
is
the size of the
pupil.
a thin
structure
that lines the
In bright light
theof
pupil
inside
the
constricts and
in dim light it
sclera.
enlarges to let in more light.
Lesson 3
Parts of the Eye
The Inner Layer
The light-sensitive cells in the
retina are called rods and cones,
each named for its basic shape.
The retina is
the light-sensitive
When light stimulates these cells,
membrane on
a nerve impulse travels to the
which images are
brain via the optic nerve, which
cast by the
is located at the back of the eye.
cornea.
Behind the iris and the pupil is
the lens of the eye.