Blind and Visually Impaired
Quoc Le
Gaby Mariz
Vanessa Romo
Lisa Yocum
Physical Structures of the Eye
and Visual Acuity
Physical structure of the Eye
How does the Eye Work?
Common Measures of Visual Acuity
What do the Results Mean?
Visually Impaired and Blind Defined
Basic Features of the Eye
Structure of the Eye
Physical Structures of the Eye
Important for Vision
Cornea-The outermost layer of the eye, it
refracts light into the lens, which further
focuses it onto the retina.
Iris-The colored part of the eye, which helps to
regulate light intake by regulating pupil size.
Pupil-The opening at the center of the iris
which expands and contracts to regulate light
intake.
Macula-Small centrally located area on retina
that gives “central vision.” (NEI. 2011)
Optic Nerve-Carries electrical stimuli from the
retina to the brain.
(NEI. 2011)
Lens
Lens- A transparent
structure that
bends in order to
focus light onto
the retina. It
consists of many
layers “like an
onion.” (National Eye
Institute,2011).
The lens thickens
as you like at
something close
and thins as you
look in the
distance
Green-Shows the
layers of the
lens.
Blue-Nuclei of other
cells in the eye.
National Eye Institute (2011).
Physical Structures of Eye
Retina-A layer at the back of the eye where light hits
photoreceptor cells. There are two types of these nerve
cells. Rods and cones, which receive light and convert this
into electrical signals delivered to the brain.
Rods allow for night vision.
Cones allow for color vision and vision in a brightly lit
environment. There are three types:
1. S cones which are sensitive to shorter wavelengths in
the VLS (blue),
2. M cones which are sensitive to medium wavelengths
(green).
3. L cones which are sensitive to longer wavelengths
(red).
Retina:
Night Vision
Shows the interactions
of nerve cell networks
operating during night
vision (rod use.)
Blue-Nerve endings of
rod bipolar cells which
receive info from the
rods.
Green- Helps facilitate
communication
through
neurotransmitters.
National Eye Institute (2011).
Cone Cells-Color and Bright Light
Vision
Cells in blue
are S cones,
sensitive to
short
wavelength
blue light.
Other cones
are M cones
sensitive to
medium
wavelength
green light.
National Eye Institute92011).
How does the Eye Work?
Light first enters the eye through the cornea which helps
refract light into the lens.
The amount of light arriving at the lens is controlled by the iris
expanding or contracting the pupil, which functions much like
a camera aperture.
As light passes through the lens it is focused on the back of
the eye at the retina.
Millions of photoreceptor cells in the retina convert this light
energy into electrical signals.
These signals travel through the optic nerve and reach the
brain, where the brain interprets them.
Common Measures of Visual
Acuity
Snellan Chart
•Developed in the mid
19th Century by the
Dutch ophthalmologist
Snellan, this chart
measures vision by
determining the
smallest line a patient
can read from 20 feet.
Common Measures of Visual
Acuity
ETDRS Chart
•Developed in 1970’s
•Backlit by a lightbox to
ensure equal illumination.
•Has the same number of
letters on all lines.
•Lines diminish in size
based on a mathematical
formula.
•Measures the smallest line
read from 20 feet.
Isn’t 20/20 a show on CBS?
How are vision results reported and what do
they mean?
The first number refers to the patient’s vision at 20 feet.
The second number refers to how many feet away a
person with average vision can read the letters.
20/20 is average vision.
20/15 is above average vision. What a visually average
person can see at 15 feet, the patient can see from 20
feet.
20/50 is below average vision. What a person with
average vision can see from 50 feet, the patient must be
at 20 feet to see.
Visual Impairments
“Low vision is defined as a visual
impairment not corrected by standard
eyeglasses, contact lenses, medication, or
surgery that interferes with the ability to
perform everyday activities.” Defined by
the WHO as only correctable to 20/60 or
less
“(Central Association for the Blind and Visually Impaired, 2012).
Partially Sighted- Refers to a loss of
vision that results in a student needing
Special Education Services.
Blind
Total Blindness- Is marked by a complete
lack of light or form.
Legal Blindness- Defined in North
America as 20/200 visual acuity or less or
as having a field of vision of 20 degrees or
less which are not correctable.
What are the major causes of
blindness and visual
impairment?
Globally
The major causes of visual impairment
are:
– Uncorrected refractive errors (myopia,
hyperopia or astigmatism): 43%
– Cataract: 33%
– Glaucoma: 2%
80% of all visual impairment can be
prevented or cured.
United States
The major causes of visual impairment in
the U.S are:
– Macular degeneration
– Cataract
– Glaucoma
– Diabetic retinopathy
Macular Degeneration
Macular degeneration affects the macula.
Associated with aging that gradually
destroys sharp, central vision.
– Central vision is needed for seeing objects
clearly and for common daily activities like
reading and driving.
Two forms of macular degeneration
Wet: occurs when abnormal blood vessels behind the
retina start to grow under the macula. These new blood
vessels tend to be very fragile and often leak blood and
fluid. The blood and fluid raise the macula from its
normal place at the back of the eye. Damage to the
macula occurs rapidly.
Dry (more common): occurs when the light-sensitive
cells in the macula slowly break down, gradually blurring
central vision in the affected eye. As dry AMD gets
worse, you may see a blurred spot in the center of your
vision. Over time, as less of the macula functions, central
vision is gradually lost in the affected eye.
Cataract
A clouding of the lens in the eye that
affects vision. Most cataracts are related
to aging.
– The lens is a clear part of the eye that helps
to focus light, or an image, on the retina.
– The lens must be clear for the retina to
receive a sharp image.
– If the lens is cloudy from a cataract, the image
you see will be blurred.
Types of cataracts
Secondary cataract. Cataracts can form after surgery
for other eye problems, such as glaucoma. Cataracts
also can develop in people who have other health
problems, such as diabetes. Cataracts are sometimes
linked to steroid use.
Traumatic cataract. Cataracts can develop after an
eye injury, sometimes years later.
Congenital cataract. Some babies are born with
cataracts or develop them in childhood, often in both
eyes. These cataracts may be so small that they do
not affect vision. If they do, the lenses may need to be
removed.
Radiation cataract. Cataracts can develop after
exposure to some types of radiation.
Glaucoma
Glaucoma is a group of diseases that damage
the eye’s optic nerve
– The optic nerve is a bundle of more than 1 million
nerve fibers. It connects the retina to the brain.
– A healthy optic nerve is necessary for good vision.
Congenital glaucoma in infants is a rare
condition that may be inherited. It is the result of
incorrect or incomplete development of the eye
drainage canals before birth.
– Can be treated with medication and surgery.
Diabetic retinopathy
Most common diabetic eye disease
Caused by changes in the blood vessels
of the retina.
– In some people with diabetic retinopathy,
blood vessels may swell and leak fluid.
– In other people, abnormal new blood vessels
grow on the surface of the retina.
Diabetic retinopathy has four
stages
Mild Nonproliferative Retinopathy. At this earliest stage,
microaneurysms occur. They are small areas of balloon-like
swelling in the retina's tiny blood vessels.
Moderate Nonproliferative Retinopathy. As the disease
progresses, some blood vessels that nourish the retina are
blocked.
Severe Nonproliferative Retinopathy. Many more blood
vessels are blocked, depriving several areas of the retina with
their blood supply. These areas of the retina send signals to the
body to grow new blood vessels for nourishment.
Proliferative Retinopathy. At this advanced stage, the signals
sent by the retina for nourishment trigger the growth of new blood
vessels. This condition is called proliferative retinopathy. These
new blood vessels are abnormal and fragile. They grow along the
retina and along the surface of the clear, vitreous gel that fills the
inside of the eye. By themselves, these blood vessels do not
cause symptoms or vision loss. However, they have thin, fragile
walls. If they leak blood, severe vision loss and even blindness
can result.
Retinal Disorders
Retinal Disorders
Retinoblastoma
Cancer that develops
in the cells of the
retina
Mutation of
chromosome 13, the
RBI Gene
Portions of the code
are missing or altered
Can develop in the
early stages of fetal
development
Symptoms
-Enlarged or dilated pupil
-Deterioration of vision
-Red and irritated eye
-Inflammation of tissue
around eye
-Crossed eyes
-Faltering grown or
delayed development
Retinal Disorders
Retinitis Pigmentosa
Deformation in the
receptors of the retina
Retina has difficulty
perceiving light
Progressive dysfunction
for the photoreceptors
(rods and cones)
Leads to cell loss and
eventual deteriorate of
several retina layers
Symptoms
-Defective dark adaptation
(night blindness)
-Loss of central vision
-Reduction of the peripheral
visual field (tunnel vision)
Retinal Disorders
Retinal Detachments
• Occur when the retina
peels away from the
underlying layer of the
support tissue
• Without rapid treatment
the entire retina may
detach and lead to
vision loss and
blindness
• Usually occurs in one
eye but has a 15%
chance of developing in
the other eye
Retinal Disorders
Retinal Detachments
• 1. Tear, break, or hole in
the retina allowing fluid
from the middle of the
eye to collect under the
retina
• 2. Inflammation, injury or
vascular abnormalities
that results in fluid
accumulating underneath
the retina. Fluid buildup
causes the layers of the
retina to separate
• 3.Traction pulls the retina
away from the layers
beneath it
Symptoms
-Flashes of light at the edge
of the field of vision
-Increase in the number of
floaters (strands of
vitreous gel)
-See a shadow across part
of the visual field that
does not go away
-New or sudden vision loss
Retinal Disorders
Retinopathy of Prematurity
 Affects babies who are born
premature/low birth weight
 Scaring or retinal detachment
Five Stages
I: Mildly abnormal blood
vessel growth
II: Moderately abnormal
blood vessel growth
III: Blood vessel growth is
severely abnormal.
IV: Severely abnormal
growth and partially detached
retina
V: There is a total retinal
detachment
Symptoms
-Abnormal eye movements
-Crossed eyes
-Severe nearsightedness
-White-looking pupils
Optic Nerve Disorders
Optic Nerve Disorders
Optic Nerve Atrophy
Tissue death of the nerve
that carries information
from the eye to the brain
Caused by:
-Poor blood flow
-Damage due to shock,
toxic substances,
radiation, or trauma
-Various eye, brain, and
central nervous system
diseases
Symptoms
-Dimming of vision
-Loss of the ability to see
fine detail
-Color seems faded
-The pupils reaction to light
may diminish and may
eventually be lost
Optic Nerve Disorders
Hemianopia
Common after stroke
and/or brain injury
Symptoms
decreased vision or
blindness in one quarter
or half of the visual field
of one or both eyes
-Blind on the same side in
both eyes. This allows
only objects to the right or
to the left sides to be
seen.
Optic Nerve Gliomas
Neurofibromatosis
Genetic disorders that
cause tumors to grow in
the nervous system
tumors grow on nerves
and produce other
abnormalities such as
skin changes, bone
deformities, and/or
damage to the eyes
Symptoms
-Cataracts at an early age
or changes in the retina
that may affect vision
-Two or more growths on
the iris or the optic nerve
Disorders of the brain that affect
vision
Disorders of the brain that affect vision
Cortical Blindness
Abnormal visual
responses due to brain
dysfunction that cannot
be attributed to the eyes
themselves
Due to:
- infections like Meningitis
and Encephalitis
-Lack of oxygen
-Drugs during pregnancy
Symptoms
-Abnormal light response
-Avoidant social gaze
-Brief fixations and
intermittent gaze
-Poor visual perception
-Visual field loss
Lens Disorders
Congenital Cataracts
What is it?
– Congenital cataract is the
clouding of the lens of the
eye which is present at
birth.
Causes
– Congenital cataracts are
rare and in most patients
no cause has been found.
They may occur in
association with other
medical problems such
as:
Down Syndrome
Trisomy 13
Rubella
Symptoms
– Grey or white cloudiness
of the pupil (which is
normally black)
– Infant does not seem to
be able to see
– “Red eye” glow of the
pupil is missing in photos,
or is different between the
two eyes.
– Unusual rapid eye
movements
Pressure Disorders
Congenital Glaucoma
What is it?
– Children with congenital
glaucoma are born with a
drainage defect which
slows the normal drainage
of fluid and leads to a
higher eye pressure than
normal. This occurs in
about one out of 10, 000
infants.
– It affects males twice as
often as females and has
no racial preference.
– In 2/3rds of the cases it
affects both eyes.
Causes
– Heritable and is caused
by abnormal eye
development.
Symptoms
– Symptoms are usually
noticed when the child is a
few months old. These
include the following:
– Cloudy eyes
– Sensitivity to light
– Excessive tearing
– Enlargement of one eye
or both eyes
Pigment Disorders
Ocular Albinism
What is it?
– Ocular albinism in an inherited condition in which the eyes
lack melanin pigment which is needed for the growth
processes that occur before birth. Therefore, the fovea does
not fully develop.
Causes
– Ocular albinism is caused by mutations in the GPR143 gene.
This gene provides instructions for making protein that plays
a role in pigmentation of the eyes and skin.
Symptoms
– Reduced visual acuity from 20/60 to 20/400 and sometimes
as good as 20/25 in African-Americans,
– Nystagmus (involuntary back-and-forth movement of the
eyes)
– Strabismus (crossed eyes or "lazy" eye)
– Sensitivity to bright light and glare.
Nystagmus: Color Vision Disorders
Achromatopsia
What is it?
– It is a rare hereditary
vision disorder that affects
1 in 33, 000 in the U.S.
– Those who have
achromatopsia do not
have normal “cone
vision.” The eyes of
achromats, lacking normal
cone vision and having
only rod vision, are not
able to adapt normally to
higher levels of
illumination. Rods do not
provide color vision or
good detail vision.
Therefore, persons with
achromatopsia are either
totally colorblind or almost
totally colorblind, and they
have poor visual acuity.
Cause
– Achromatopsia is
hereditary.
Symptoms
– Photophobia (sensitivity to
light)
– Poor visual acuity
– Color blindness
– Nystagmus
Aniridia
What is it?
– It is a condition in which the individual is born
without the iris. The iris is the colored part of the
eye that controls the amount of light that goes
into the eye.
Cause
-2/3rd of the time it is hereditary.
Symptoms
– Decreased visual acuity
– Photophobia (sensitivity to light)
– Dry eye
Other Structural Defects
Hyperopia (farsightedness)
What is it?
– Individuals with hyperopia have difficulty viewing objects
up close. Farsightedness occurs if your eyeball is too short
or the cornea has too little curvature, so light entering your
eye is not focused correctly.
Cause
– This vision problem occurs when light rays entering the
eye focus behind the retina, rather than directly on it. The
eyeball of a farsighted person is shorter than normal.
Symptoms
– Common signs of farsightedness include difficulty in
concentrating and maintaining a clear focus on near
objects, eye strain, fatigue and/or headaches after close
work, aching or burning eyes, irritability or nervousness
after sustained concentration.
Myopia (Nearsightedness)
What is it?
– Nearsightedness is when light entering the eye is
focused incorrectly, making distant objects appear
blurred. Nearsightedness is a type of refractive error
of the eye.
Cause
– Occurs equally in males and females.
– People with a family history of Myopia than they are
more likely to develop it.
Symptoms
– Difficulty seeing objects at a distance.
– Eyestrain
Amblyopia (Lazy Eye)
What is it?
– Amblyopia, or "lazy eye," is the loss of one eye's ability to see
details. It is the most common cause of vision problems in
children.
Causes
– Amblyopia occurs when the nerve pathway from one eye to the
brain does not develop during childhood. This occurs because
the abnormal eye sends a blurred image or the wrong image to
the brain.
– Strabismus is the most common cause of amblyopia. There is
often a family history of this condition.
– Childhood cataracts
– Farsightedness, nearsightedness, or astigmatism, especially if it
is greater in one eye.
Symptoms
– Eyes that turn in or out
– Eyes that do not appear to work together
– Inability to judge depth correctly
– Poor vision in one eye
Astigmatism
What is it?
– Astigmatism is a condition in which the uneven curvature
of the cornea blurs and distorts both distant and near
objects. The cornea is abnormally curved like the back of a
spoon which causes vision to be out of focus.
Causes
– The specific cause is unknown. It is usually present from
birth, and often occurs together with nearsightedness or
farsightedness.
Symptoms
– Astigmatism makes it difficult to see fine details, either
close up or from a distance.
Educational Implications
Student may need optical aids like:
- sunglasses or tinted contact lenses to cope with bright
light in the classroom
-eye patch
-thick glasses
-protective eyewear during sports and other hazardous
activities.
Student may need magnifiers to help with reading
Increased illumination
Some are recommended to avoid contact sports and
strenuous activity
Educational Implications
– Some students may have difficulties reading and
playing ball sports due to the low visual acuity.
– Some potential modifications include:
Moving the student’s seat to the front row so the
student can see the chalkboard, marker board,
overhead projector, or video
Changing where the student sits so they can avoid
glare from overhead lights or windows.
Provide the student with a hard copy of the material
that is presented on the white board or via the
overhead project.
Allow the student to copy another student’s notes if
they can’t see the board.
Enlarge tests and handouts.
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