Call our free helpline0808 808 3555
Call our free helpline
0808 808 3555
Some children and adults with hemiplegia may have difficulties
with certain aspects of seeing. This information explains how we
see, which aspects of seeing may be affected in people with
hemiplegia, and how these issues can be identified and managed.
The eyes work like a pair of cameras to form an image to send to
the brain. The cornea is the curved front part of the eye, the iris
is the coloured part and the pupil is the hole in the middle.
Behind the pupil there is a clear lens. At the back of the eye is
Together, the cornea and lens bend the light rays entering
through the pupil so that they come into focus on the retina. This
process of light bending is called refraction. A refractive error
leads to a loss of focus. The lens can change shape so that objects
at different distances can be seen clearly. This process is called
accommodation (see 'Eye function impairments' section).
The light sensitive cells in the retina are called rods and
cones; they convert the picture on the retina into tiny electrical
signals which run along the optic nerves, through the brain to the
back part, called the occipital lobes. On their way to the brain,
the two optic nerves join in a crossover junction, so that the
messages from the two eyes are mingled.
In this way, the picture of what we see to our left (with each
eye) is created in the right side of the brain, and the picture of
what we see to our right (with each eye) is created in the left
side of the brain. The brain 'knits together' the images received
by each eye and this helps to create 3D vision.
Several parts of the brain work together to create the picture
that we see. The back of the brain (the occipital lobes) analyses
the picture information from the eyes for clarity, colour, shades
of grey, and the extent of the area that can be seen - called the
visual fields. The parts of the brain just behind the ears are
called the temporal lobes. These contain a powerful 'search
engine'. The information from the occipital lobes is sent here
along a pathway called the 'ventral stream'.
This information is compared with our own stored picture
information: if it matches, the picture is recognised. If it does
not, the brain learns to recognise it in the future. Above the
temporal lobes are the posterior parietal lobes. They receive the
information from the back of the brain along a pathway called the
dorsal stream. From this they construct a 3D map of our
What we are looking at is seen and interpreted in the temporal
lobes. The posterior parietal lobes map the scene, so that we can
use our vision to guide our movements. The frontal lobes help us to
focus our attention on certain items in the overall visual scene.
They are closely linked to our conscious recognition vision in the
temporal lobes, which tells us what things are, and our
non-conscious mapping vision, which tells us where things are.
Children with hemiplegia can have difficulties with many aspects
of eye function and vision. As hemiplegia results from an injury
that affects one side of the brain more than the other, this may
result in visual field defects (see below). A hemi-field defect is
the type of visual impairment that doctors may most commonly
suspect in your child. However, it is important to be aware of the
other eye and other potential visual difficulties.
Refractive errors: Focusing issues that can be
corrected by wearing spectacles. To diagnosis refractive errors, an
optometrist or ophthalmologist carries out an eye test called
Myopia or short-sightedness: When looking at
distant objects, the image falls short of the retina and so vision
is blurred. Near objects can be seen clearly. This issue can be
corrected by wearing glasses.
Hypermetropia or long-sightedness: When looking
at near objects, the image falls behind the retina and so vision is
blurred. Distant objects are usually seen clearly. Again, this
issue can be corrected by wearing glasses.
Astigmatism: The curvature of the eye is
uneven, causing uneven image placement. Glasses can correct the
Squint: The eyes are not straight. If the brain
receives very different images from each eye it cannot knit them
together and may start to 'switch off' the vision from one eye,
causing vision in it to be reduced. This is called amblyopia, and
it can be treated by patching the unaffected eye. This type of
treatment is usually undertaken by an orthoptist working in an eye
Accommodative difficulties: This is when the
lens fails to adjust its shape. As a result, near objects may not
be seen clearly. An optometrist or ophthalmologist can test for
this and glasses can help.
Eye movement difficulties: These can affect the
movements needed to follow a moving object, or when shifting gaze
from one thing to another. Eye movement issues can usually be
overcome by moving head and eyes together.
In hemiplegia, if the brain injury affects the back part of the
brain, vision can be lost or disturbed on the opposite side of the
injury. Because some of the information from each eye is sent to
both sides of the brain, half of the field provided by each eye can
be affected. This is usually called a hemi-field defect or a
If the left side of the brain has been injured, causing a right
hemiplegia, then there may be loss or impairment of vision to the
right side of the body, and vice versa. Lack of vision to the right
in each eye is called right hemianopia, and lack of vision to the
left in each eye is called left hemianopia. Sometimes the word
homonymous hemianopia is used: this means that the vision on the
same side in each eye is lost.
There are other patterns of field defect depending on the exact
location of the brain injury, but hemi-field defects are most
likely in hemiplegia.
How do we know if visual field defects are
Children and young people might not be able to report what they
can't do or see and may not be aware that their experience is
different from that of other children. Field defects might be
'suspected' either because a health professional considers it a
likely issue, or because of what can be observed. Remember,
however, that there can often be more than one explanation for some
What can be observed?
If you are a parent, observe what your child does and doesn't
notice in a variety of situations. Does your child often seem to
turn his or her face in one direction? Notice what your child sees
when seated at the meal table, or on the floor with toys all
around. Does she or he seem to 'miss' anything to either side? How
does she or he react when something appears on one side from
behind? When your child is walking or moving, notice whether she or
he bumps into things on one side.
Visual fields can be tested by a method known as 'confrontation
testing'. The tester asks the person to look straight at them, and
then introduces an object into different parts of the visual field.
The person being tested reports when they can see the object.
This test can be carried out on young children, but it can be
difficult as it depends on the child understanding the instructions
and cooperating. In very young children, you can still get useful
information by observing when they turn to look at something
introduced from behind. This is sometimes called modified
You can carry out very detailed visual field testing using a
specialised piece of equipment called a perimeter, available in an
eye clinic. Many children from about the age of eight years can do
this type of test.
Continued observations over time are very important. Sometimes a
visual field defect might be suspected or assumed and described in
medical letters, but this should always be clarified by testing as
far as is possible. As limb movements are also limited, this can
also affect your child's ability to reach or move on one side.
Sometimes there may be a relative lack of awareness in part of
the visual field, rather than an actual lack of visual field. This
is called hemi-inattention. Your child may not notice things placed
in the affected area when they are attracted by an object in the
unaffected area. However, if that object is removed, they have more
attention available to 'notice' objects in the affected part of
their visual field.
What can be done to help?
Here are some tips to help your child manage their sight
Of course, you should also consider guidance from therapists
treating your child's hemiplegia, depending on his or her current
Visual acuity means clarity of vision, or how sharply-focused
something appears. Reduced visual acuity means that things appear
less clear than they should. Things will look blurred or 'out of
focus'. Visual acuity can be affected by a refractive error (see
previous section), and correction by glasses can restore normal
visual acuity. However, any injury affecting the brain can reduce
visual acuity and this will not be correctable with glasses.
Visual acuity can be measured by specialists using cards that
show pictures or letters. Your child does not have to be able to
talk to have this type of test. If visual acuity is reduced, then
your child may have difficulty in seeing small detail.
Vision begins with visual detection (seeing that something is
there). Visual perceptual skills are those skills that support a
rich interpretation of what is seen. They include the ability to
recognise shape, form and size, despite circumstances that might
limit the capacity to do so.
For example, visual perceptual skills underlie the ability to
see shapes as distinct even when they are overlapping, or to see
the whole of something despite parts being missing. Visual
perceptual skills are useful in a variety of everyday tasks, and
they support the development of academic skills such as reading,
writing and mathematics.
Visual perceptual difficulties are found in a small proportion
of children with all types of cerebral palsy. Children with this
type of impairment may have difficulties with putting puzzle pieces
together, or with copying or drawing. They may also have
difficulties coordinating vision and movement, sometimes called
Identifying visual perceptual and visuo-motor
Formal testing can be carried out in children from the age of
four. These tests should ideally be considered alongside what else
is known about your child's learning and academic achievements.
Specific tasks might be recommended to see if your child's
skills can improve. However, these skills cannot always be 'learnt'
and may not improve with practice. A more practical approach is
often to help your child use their strengths or other strategies to
achieve a given goal.
You and your child's teacher will work together to introduce her
or him to letters and early reading activities at the right time.
Many of the issues already mentioned could have some impact on your
child's ability to make steady progress with reading and writing.
And there are also other difficulties relating to hemiplegia that
can affect some children's progress with these skills. Your child's
teacher and therapists should be able to work together to find out
why your child might be having difficulty and the best way to
Sometimes other difficulties with vision can occur in children
with hemiplegia. When brain injury, rather than eye abnormality,
causes vision difficulties, this is called cerebral visual
impairment. Visual field defects and eye movement issues are part
of the cerebral visual impairment 'spectrum'.
Many other types of visual difficulty have been reported in
children with brain injury, and some of these are described below.
It is important to remember that these issues do not occur in all
children with hemiplegia or other forms of cerebral palsy.