Chapter 2

Teaching Students with Sensory Impairments
Definitions, Identification, and Supportive Professionals
Dolly Bhargava
Vision plays an important role in student growth, development and daily performance.
Vision impairment is identified as one of the ten most prevalent causes of disability in
the United States. A fact sheet produced by the National Information Center for
Children and Youth with Disabilities in 1997 stated that the prevalence of visual
impairments in individuals under the age of 18 is 12.2 per 1,000.
There is a wide range of cause and type of vision impairment. Although each student is
unique, in general terms, a student is identified as having vision impairment when his or
her vision disorder affects the ability to function in life to such a degree that the eyes
cannot be corrected with glasses, contact lenses, medications or surgery. In such
cases special instructional techniques, materials or assistive devices are needed for
optimum learning to take place (Miller & Levack, 1997).
To effectively teach students with vision impairment, teachers need to become familiar
with vision-related concepts. The information below will briefly outline the nature of
vision impairment and provide you with useful current definitions, not only of blindness,
but also of the related term vision impairment, and deal in particular with the educational
requirements of students who have low vision. The chapter will provide you with
information on ways of identifying students with vision impairments in the classroom,
discuss their learning characteristics, and briefly focus on the several types of
professionals who can be of assistance in their diagnosis and education.
1. Vision
Mike Offord
Vision is a dynamic, always changing process of organizing, interpreting and
understanding what is seen. It is a process that integrates sensory and motor
information generated by the brain and body to derive meaning and direct movement.
The use of vision is actually developed like walking and talking. It is learned over time
from birth on up by our experiences and how we react and solve problems. It differs
from eyesight because eyesight is our ability to see, a sense that most of us are born
with, and vision is actually a LEARNED process. The visual skills we learn early on
provide the foundation for later visual complexities. Any weak link in the visual process
can affect the outcome, especially if the visual system is under stress.
Basically, we use vision to guide motor behaviour, like catch a ball; interpret space and
time, like when we give directions and say "it will take 10 minutes if we turn left at the
light coming up in two blocks"; and integrate information from our other senses (hearing,
touch, taste and smell), so we may think, understand and react to the world around us.
Vision allows us to take what we see and process this light information so we can -
Identify what we see by where it is, how far away it is, how big it is, how fast it is
moving, what texture it has, etc.
Store this current information for future retrieval.
Integrate the sight information with all our other senses - touch, hearing, taste
and smell.
Compare this information to previously stored information in order to confirm prior
experience or reconstruct a prior experience if necessary.
Derive meaning from both the new information and past information.
Decide the relationship between where we are and where it is, or find out where
we are in space.
Act on this new meaning.
Use this new perception to direct movement or thought.
2. Definitions of Vision Impairment
Dolly Bhargava
A student with a vision impairment is part of a heterogeneous group whose one common
characteristic is some degree of vision loss. Vision is a perceptual process with three
elements: the eye, the optic pathway and the brain (MacLean, 1998). For vision to occur,
all three elements must be functioning. Educationally, there are three major groups of
students (or learners) with vision impairments in our schools:
1. Learners who are “educationally blind”: These students have little or no functional
vision for learning and primarily use Braille, audio and tactile aids in their learning.
2. Learners with low vision: After correction (i.e., with glasses), these students are
able to use vision for learning and are generally dependent on low-vision aids and
environmental modifications for assistance;
3. Learners with correctable low vision. These are students who, after correction, can
use their vision effectively and without too much extra help (Kelley, Gale & Blatch,
1998, p. 35).
These three categories are helpful to you as a teacher as they suggest the teaching and
learning frameworks that must be set in place so that each student can properly access
the curriculum.
A. How is Vision Measured?
Dolly Bhargava
In two ways: First by measuring a students’ visual acuity and then their field of
A-1. Visual Acuity
Visual acuity refers to the ability to see sharply and clearly at both short and
long distances to distinguish detail and shape. Each eye has its own level of
visual acuity and the level of visual acuity of each eye can differ
considerably. Visual acuity is usually measured by determining the smallest
letter or picture or symbol that a person can read on a standardized eye
examination chart.
The visual acuity measurement is expressed as a fraction. Normal vision is
defined as a person having 20/20 or 6/6 visual acuity. The numerator (top
number) refers to the distance a person stands from the eye examination
chart. In the United States this number generally represents a distance of
about 20 feet. In countries where meters are used, the distance is 6 meters
long, approximately 20 feet. The denominator (bottom number) indicates
the smallest letter, number or symbol that the person can read. The lower
the bottom number in the visual acuity ratio, the better the acuity. The
greater the bottom number, the worse the acuity. For example, 20/100 is a
better visual acuity than 20/200 acuity.
Examples of what a person with different visual acuities may see for distance
vision Mike Offord.
Examples of what a person with different visual acuities may see at an eye chart
at 6 metres Mike Offord.
Approximations of Vision with Different Acuities – Distance Vision
Approximations of Vision with Different Acuities – Eye Chart at 6 metres
2. Field of Vision
Field of Vision refers to the area within the environment that a person can
see when looking straight ahead. If the field of vision is restricted then the
person will miss seeing some parts of the whole scene or image (Orlansky,
1977). The normal field of vision of is 180 degrees.
Certain measures of visual acuity and field of vision have special
significance in terms of diagnosing vision impairments. We will use these
measurements to describe two types of vision impairment that are
commonly used in the educational context: (a) low vision, and (b) legal
blindness. It is important to note that definitions of these terms may vary.
However, for the purposes of this handbook they are as follows:
A-3. Legal Blindness
Students who are legally blind
As an eligibility criterion for government assistance, a legal definition of
blindness is used. In the USA, to be considered legally blind, an
individual's visual acuity must be equal to or less than 20/200 with the best
possible correction, or a visual field of 10 degrees or less. Someone with
a visual acuity of 20/200 can see at 20 feet what someone without a vision
impairment can see at 200 feet. In countries where a metric system is
used a student is considered "legally blind" when his/her visual acuity is
6/60 What a person without vision impairment vision would see at 60
meters is what the student who is legally blind sees at 6 meters or less in
the better eye, even with correction. A person who is legally blind has a
field of view which is 10 degrees or less in the better eye (Kelley & Gale,
1998). Blindness cannot be corrected by medical or surgical means or
corrective eye wear. The student needs instruction that emphasizes the
use of his or her other senses, for example, touch (i.e., Braille) and
hearing (i.e., auditory tapes) to learn about the world and complete tasks
(Orlansky, 1977; Lewis & Allman, 2000).
A-4. Low Vision
Students who have Low Vision
The definition of low vision for most legal purposes in the United State is a
visual acuity between 20/70 and 20/200 with correction in the best eye, or a
field of vision less than 20 degrees, compared to normal field of vision of 180
degrees. In countries using a metric system low vision is denoted by a
student having a visual acuity of less than 6/18 (what a person with normal
vision would see at 18 meters is what the student with low vision sees at 6
meters) or less or if his/her field of view is 20 degrees or less (Best & Corn,
1993 cited in Kelley & Gale, 1998). Low vision is not the same as
blindness, as the person with low vision has some sight, yet has difficulty
accomplishing visual tasks using sight. “A student who has low vision can
enhance his or her ability to accomplish tasks with the use of compensatory
visual strategies, low vision devices, and environmental modifications” (Corn
& Koenig, 1996, p.4). This process includes the provision of visual
strategies ( i.e., enlarged print); specialized optical devices ( i.e., magnifiers
or telescopes); non-optical devices ( i.e., bold line black markers) and
environmental modifications ( i.e., changing seating position in class) (Lewis
& Allman, 2000).
When determining the needs and abilities of a student with vision impairment it is
important to look beyond the label e.g. ‘low vision’ or a numerical value e.g. 20/200.
Instead we need to appreciate the fact that there is no “typical” student with vision
impairment. The impact of the vision impairment on a student will depend upon on the
following factors:
- type of eye condition
- age of onset
- degree of functional vision
- visual efficiency
- type of intervention provided
To help explain this, let’s consider one of these factors. The age of onset of vision
impairment has different effects on the child’s communication and cognitive
development. Consider the cases of Joanne and Rita, both of whom are six years of
age and have a vision impairment. Joanne was born blind, whereas Rita was born with
normal vision but became blind at the age of three as a result of a car accident. One of
the areas of development effected by vision impairment is the development of self help
skills. Self-help includes self-routines such as eating, dressing, toileting and grooming.
Many of these self-help skills are usually learned through observation. There are
qualitative differences between the self-help abilities of Rita and Joanne. For example,
Rita who became adventitiously blind had the opportunity to see different types of foods,
eating utensils, mealtime locations and seen others eat. Whereas, Joanne who was
congenitally blind had never had sight required specific guidance and a variety of
experiences in order to understand concepts related to eating.
Therefore, every student with vision impairment has unique needs and abilities.
Understanding the background history will determine unique educational support needs
and determine the best type of assistance (Anderson, 2003).