Psychology 2043A/B Lecture Notes - Lecture 10: Cortical Visual Impairment, Cuisenaire Rods, Visual Acuity

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PSYCH 2043B: Developmental Disorders
Week 10: Children with Visual Impairments
March 14
CHAPTER 10 – BLINDNESS AND LOW VISION
Tremendous importance of vision in obtaining information about our world
Students with visual impairments may learn to make good use of their other senses
Never totally compensate for loss of vision
DEFINITIONS
Under IDEA, visual impairment has both legal and educational definitions
Legal Definition of Blindness
Visual acuity = ability to clearly distinguish forms or discriminate among details
oMost often measured by reading letters, numbers, or other symbols from the Snellen
Eye Chart
20/20 vision does not mean perfect vision – indicates that at a distance of 20 feet, the eye can
see what a normally seeing eye sees from 20 feet
Someone whose visual acuity is 20/200 or less in the better eye with use of corrective lens is
considered legally blind
Any individual with visual acuity no better than 20/70 after correction is considered partially
sighted
One may also be considered legally blind if field of vision is extremely restricted
Normal eye can see objects within a range of 160-170 degrees
A person whose vision is restricted to an area of 20 degrees or less is considered legally blind
Those with tunnel vision may have good central vision but poor peripheral vision at the outer
ranges of the visual field
Children who are legally blind are eligible to receive a wide variety of services
Educational Definitions of Visual Impairments
Visual impairment according to IDEA = impairment in vision that adversely affects a child’s
educational performance, even with correction
May display a wide range of visual abilities
A student that is totally blind receives no useful information through vision
A child who is functionally blind has so little vision that they learn primarily through auditory and
tactile senses; however, may be able to use limited vision to supplement
A child with low vision uses vision as a primary means of learning but may supplement visual
information with tactile and auditory input
Age at Onset
Can be congenital (present at birth) or adventitious (acquired)
Most impairments of school-age children are congenital
CHARACTERISTICS
Cognition and Language
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Vision enables children to organize and make connections between different experiences
Children who are blind perform more poorly on cognitive tasks requiring comprehension or
relating different items of information
Impaired or absent vision makes it difficult to see the connections between experiences
Abstract concepts, analogies, and idiomatic expressions can be particularly difficult for children
who cannot see
Motor Development and Mobility
Often leads to delays or deficits in motor development
Four important functions in acquisition of motor skills:
oMotivation
oSpatial awareness
oProtection
oFeedback
Absence of sight or clear vision reduces one’s motivation to move
A child without clear vision may move less often because movements in the past have resulted
in painful contact with the environment
Even limited vision can have negative effects on motor development
Children with low vision have poorer motor skills than do children who are sighted
Gross motor skills, especially balance, are particularly weak
Frequently cannot perform motor activities through imitation
Social Adjustment and Interaction
Children with visual impairments play and interact less during free time
Often delayed in the development of social skills
Many struggle with social isolation and must work harder than sighted peers to make and
maintain friendships
Low incidence of the disability
oLimited amount of people experiencing the same challenges because of visual
impairments
Inability to see and respond to the social signals of others reduces opportunities for reciprocal
interactions
Some engage in repetitive body movements or other behaviours
oEx. Body rocking, eye pressing and poking, hand flapping, head weaving
These behaviours were traditionally referred to as “blindisms”
Stereotypic behaviour is a more clearly defined term that subsumes blindisms and mannerisms
Stereotypic behaviour can place a person at a greater social disadvantage because these actions
are conspicuous and may call negative attention to the person
Unknown why many children with visual impairments engage in stereotypic behaviours
Behavioural interventions may help reduce stereotypic behaviours
Many with visual impairments report that the biggest difficulty socially is dealing with attitudes
and behaviour of sighted people
PREVALENCE
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Estimated 25 million + people in US living with a vision loss
Visual impairment requiring special education is a low incidence disability
Children with visual impairments amounts to about 2 children in 1000
Many with visual impairments have one or more additional disabilities, therefore may be
classified under other disability categories
Number of students with visual impairments is larger than the data reported for IDEA
TYPES AND CAUSES OF VISUAL IMPAIRMENTS
How We See
Effective vision requires proper functioning of:
oOptical system
oMuscular system
oNervous system
Optical system:
oCollects and focuses light energy reflected from objects in the visual field
oLight first hits the cornea – curved transparent membrane that protects the eye
oThen passes through the aqueous humor, a watery liquid that fills the front chamber
oNext, passes through the pupil, circular hole in the center of the coloured iris
oThe pupil contracts or expands to regulate the amount of light entering the eye
oThen passes through the lens, a transparent, elastic structure
oAfter the light passes through the vitreous humor, a jellylike substance that fills most of
the eye’s interior, it reaches the retina
oRetina – multi-layered sheet of nerve tissue at the back of the eye
Muscular system:
oEnables ocular motility – eye’s ability to move
oSix muscles attached to the outside of each eye allow it to move
oPlay a part in depth perception (binocular vision) – ability to fuse separate images from
each eye into a single, 3D image
oTiny muscles adjust the shape of the lens, making it thicker or thinner, so the eye can
bring objects at diff distances into sharp focus (accommodation)
Nervous system:
oConverts light energy into electrical impulses
oTransmits that information to the brain, where it is processed into visual images
oRetina consists of light receptors called cones and rods
oCones enable detection of colour and detail
Located in the center of the retina
Function best in good light
oRods are responsible for peripheral vision, detection of movement, and vision in dim
light
Located around the periphery of the retina
oOptic nerve carries electrical messages from the cones and rods directly to the visual
cortex
Causes of Visual Impairments
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