Cortical Visual Impairment An introduction This is a general introduction to Cortical Visual Impairment intended for families and support workers who may live with or support children and adults with learning disabilities or acquired brain injuries. Please also visit our Cerebral Visual Impairment section for more detailed information. Definition Cortical Visual Impairment (CVI) refers to visual problems a child or adult may experience as a result of damage to the parts of the brain that deal with vision. You may also hear CVI being referred to as Cerebral Visual Impairment, Cognitive Visual Impairment or Visual Processing Disorder. It is thought that 40% of the brain is concerned with processing vision. When children or adults have damage to the brain it should not come as a surprise that some will therefore experience problems with their vision. CVI can occur before or during birth or later as a result of events such as disease or injury. CVI occurs within the brain, not within the eye, therefore an optometrist (optician) will be unlikely to be able to diagnose CVI from a standard eye examination. It may well be that upon examination the eye is healthy but the child or adult nevertheless displays behaviour that leads others to believe they may have problems seeing things or recognising things. However, it is worth bearing in mind that children and adults with CVI might also need to wear glasses due to correctable conditions such as short sightedness or long sightedness. CVI describes a range of observable behaviours and difficulties that may indicate that the child or adult has some significant difficulties in processing vision.
The type of difficulties you might observe may fall into these broad categories. Children and adults may have problems with moving around and getting places problems with recognising shapes, faces and objects problems with focusing upon near objects problems with tracking or following objects as the person may be unable to move their eyes quickly enough. problems caused by Visual Field Losses such as not being able to see in the lower, or upper part of their vision. Or being unable to see to the left or the right. We have advice at the end of this factsheet about getting help if you suspect your child or the person you support has a Cortical Visual Impairment. How do we see? The role of the brain in seeing.
To be able to see our world clearly, and to understand and react to what we see, we need our eyes and our brain to be able to function together. Our eyes collect reflected light from the world around us. Light entering the eye is focussed upon the layer within the back of the eye called the retina. The retina turns reflected light into neural / electric signals that travel from the back of each eye along the optic nerve. It is these signals that we turn into recognisable images within the brain. The optic nerve from each eye combines and crosses within the brain. The signals from the optic nerve then reach the back of the brain at the visual cortex within the occipital lobe. This leads to the light received from the left visual field of vision being perceived as images in the right side of the brain, and light received from the right field of vision being perceived as images in the left side of the brain. All the signals that reach the visual cortex from the optic nerves are then seen as a single image. The visual process is complex and reliant upon a healthy and un-impaired visual pathway within the brain. The information from the optic nerve is distributed from the occipital lobe and follows two streams ; the Dorsal stream and the Ventral stream. The two streams work in harmony - allowing us to use our subconscious vision (such as flinching from objects as they approach us) and our conscious vision (such as undertaking complex visual tasks such as driving or map reading).
The Dorsal stream is concerned with managing lots of information at the same time and also in maintaining our attention upon that information. The Dorsal stream is concerned with our movement or motor skills including how we move our head and eyes rapidly to gather and observe visual information. The Dorsal stream is also concerned with making decisions about how we respond to the visual information we are receiving. The Dorsal stream flows from the back of the brain, through the top of the section of the brain to the front of the brain. The Ventral stream is concerned with recognising objects, shapes faces and places etc. It enables us to differentiate between different things we see and to name them. The Ventral stream enables us to recognise and respond to visual information such as recognising routes, familiar and unfamiliar people or places, and to recognise safety, danger and risk. The Ventral stream runs from the occipital lobes to the lower sides of the brain. What might be the impact upon vision by damage to the brain? Damage to specific areas of the brain may have a particular impact upon our vision. The type of damage caused to sight depends on the area, or areas, of damage to the brain. Damage to the optic nerve within the brain will lead to indistinct or incomplete images being received by the brain. If the optic nerve is severed or diseased then potentially sight loss can occur from one eye, or both, depending on the location of damage to the nerve. If the area of Dorsal stream in damaged, perhaps due to cerebral palsy at birth or an accident later in life, the person may have difficulties with their movement. The person may have difficulty in coping with too much visual information and visual movement around them. They may have difficulty moving their head or eyes. They may not be able to attend to visual information or be unable to concentrate on visual tasks. Damage to the Ventral stream may lead to people not being able to recognise or see faces or objects people may be face blind. People may not be able to differentiate between familiar or
unfamiliar people or objects, or may not be able to recognise what to do with objects, may not visually recognise risk or may not recognise places or faces. Recognising if someone has Cortical Visual Impairment Once you have ruled out that the person s visual difficulty is not caused by a diagnosable eyesight problem, you may want to consider using one of the downloadable observational tools to assess the type of difficulty the person may be experiencing. We also have some strategies that you might wish to follow to help support the person. The type of difficulties you might observe may fall into these broad categories. Children and adults may have problems with moving around and getting places problems with recognising shapes, faces and objects problems with focusing for near objects and coping with lots of objects cluttered together problems with tracking or following objects or fast movements due being unable to move their eyes quickly enough problems caused by Visual Field Loss such as not being able to see in the lower, or upper part of vision. Or being unable to see to the left or the right It is very important that any sudden changes to a person s vision are acted upon and that the child or adult sees their GP or Optometrist as soon as possible. Sudden changes to a child s or adult s visual functioning may denote a more serious problem. More information - assessment and helpful strategies.
Conditions that may be associated with Cortical Visual Impairment Premature birth Hydrocephalus / Microcephalus Obstetric Complications Cerebral Haemorrhage Meningitis / Encephalitis Head Injury Cerebral palsy Strabismus (Squint) Brain tumour Stroke Getting Help. As already mentioned a person can have healthy eyes yet still experience visual impairment due to damage to the brain. This means that an optometrist (optician) will be unlikely to be able to diagnose CVI from a standard eye examination. It is important that the adult s or child s eye health is checked and to find out whether the child or adult needs glasses. Six out of ten children and adults with learning disabilities need to wear glasses. Children and adults with a learning disability are 10 times more likely to have a sight problem than other people. There is no national scheme or service to recognise and diagnose CVI you may ask your optometrist or GP to refer you to an ophthalmologist (eye doctor) who may be able to give you further advice about CVI. You could ask your GP to refer you to specialist such a neurologist or paediatric specialist for further advice. You may wish to discuss your child s vision with a Qualified Teacher for the Visually Impaired or refer an adult you support to a Behavioural Support Team. Please also visit our Cerebral Vision Impairment section for more detailed information.