What is CVI?


Pick & Mix, A-Z Labels

You only need to look at topics relevant to the person.You only need to look at topics relevant to the person.

We use the term 'person' for the person with CVI. This may be you, or someone you support and care for. It may be a child or adult.

Please take a few minutes to read our short Introduction page about labels.

Labels Commonly Associated with CVI
(Alphabetically Listed)

Additional Support Needs (ASN)
This is a general term where a child needs extra help in some areas.
See Developmental Delay, below.

This is an inability to read words due to an injury to the part of the brain (usually on the left side) responsible for seeing letters and words. The commonest cause is a stroke. For more information click here.

Attention Deficit Hyperactivity Disorder (ADHD)
The original name, going back over a hundred years, was 'hyperkinetic impulse disorder', and for a while was Attention Deficit Disorder (ADD). In the late 1980s, the hyperactivity, from the original hyperkinetic (frantic movements) observations, was added, and the condition became ADHD. The signs of ADHD include difficulty staying focused, and being forgetful, careless, disorganised, impatient, irresponsible, impulsive and inconsiderate. ADHD can affect learning and social relationships.

There are different assessments for ADHD, and for the diagnosis to be confirmed the difficulties must be ongoing, usually from childhood. If the person has a developmental disorder, or is simply having a difficult time, or has other conditions that could explain the difficulties, then they may not meet the criteria for ADHD.

What about CVI? CVI can lead to all of the difficulties children with ADHD have. This does not mean that everyone with ADHD has CVI, but some will, and we think it is worth checking. Many of the suggestions for CVI, like reducing crowding and complexity, slowing things down, building memories and ensuring emotional and physical wellbeing, will help a person with ADHD behaviours caused by CVI. If the behaviours are not caused by CVI, the suggestions certainly won't harm, and could still help. If CVI is diagnosed, then, in terms of labels, the person arguably no longer has ADHD. They have CVI leading to ADHD like reactive behaviours.

Further reading UKs NHS Pages on ADHD.

Auditory Processing Disorder (APD)
Also sometimes called Central Auditory Processing Disorder (CAPD).

APD is a controversial disorder, with little agreement of what it is. APD occurs where the hearing system is normal, but the processing of sounds is not typical. APD may cause many different difficulties, in some affecting speech development, and in turn, social relationships and learning as well. The difficulties are real, even if there is disagreement over what the label APD means. Because the definition, assessment and terminology have not been clearly agreed, this means that research on the subject has been limited, and at times challenged.

Many people with CVI describe auditory processing difficulties similar to those described by people with APD (described in our page Cerebral Auditory Impairment). It is possible that there may be a matching connection between the visual processing difficulties for those with CVI and the auditory processing difficulties associated with APD.

Further reading Central Auditory Processing Disorder & CVI Paper

Autism, Autistic Spectrum & Aspergers Syndrome
A wide range of difficulties come under the 'autistic spectrum' umbrella. Social communication is a key difficulty, with other challenges affecting behaviour and learning. CVI can cause behaviours very similar to those of autism. Some people can have CVI and autism, where the CVI does not fully explain all the autistic challenges. Other people with autism can show visual perception difficulties (see below) that are not currently thought of as being those of CVI.

Aspergers Syndrome is a type of autism where the person has average or above average learning abilities, with some of the challenges of autism, particularly around social communication. Some countries no longer use the term Aspergers syndrome. As with autism, CVI can cause the challenges of Aspergers, be partly responsible, or not present at all.

In line with current assessment criteria, a person can have CVI and autism. What you need to understand for the person, is whether their CVI is causing the autistic behaviours, because if so, support that helps such people access and understand what they were previously missing, in our experience can result in exciting outcomes.

Further reading CVI Autism Blog

Deafblind / Dual Sensory Impaired / Multi-Sensory Impaired (MSI)
These terms apply when both hearing and vision are not working typically. Traditionally this has related to the eyes and hearing systems, rather than to visual and auditory brain processing systems. For some, their CVI and parallel auditory processing challenges are so severe that they are functionally deaf and blind, despite typically working eyes and hearing systems.

Further reading Central Auditory Processing Disorder & CVI Paper

Central Auditory Processing Disorder (CAPD)
See Auditory Processing Disorder, above

Challenging Behaviour / Distressed Behaviour
These terms are sometimes used when a person does not meet the criteria for another condition, typically autism, yet has some of the behaviours affecting both the person and possibly others around them. The behaviours can be very similar to autism, and either milder, or without the other behaviours.
See also, Autism, above.

Complex Needs / Complex Additional Support Needs
Complex needs typically refers to a mix of medical needs and developmental difficulties. Sometimes this term is just used to mean developmental delays where there are many (and so, complex) causes. Without a list of the individual needs and difficulties, this term has extremely limited value.
See Developmental Delay, below.

Cortical Visual Impairment
Cortical Visual Impairment was the term used for brain based visual impairments, when it was thought the difficulties were limited to visual field, visual acuity, colour and contrast deficits. This was replaced with the term Cerebral Visual Impairment in the 1990s, although it is still used in some countries. They are not different conditions and do not refer to different parts of the brain or different processes. They have the same meaning, although some have argued otherwise.

Further reading: Newsletter 17 Cerebral or Cortical?

Developmental Coordination Disorder (DCD)
DCD is all about motor skills. Motor skills are our movements and they are often broken down into two categories: 1) Gross motor skills, which are the big movements like walking and running, and 2) Fine motor skills, which are the smaller movements like holding a pencil, tying laces or cutting food with a knife and fork.

DCD is diagnosed when the motor skills are delayed or not typical, and if there are no other conditions to explain the difficulties. Other conditions include visual impairments. This means that a child cannot have both CVI and DCD, because CVI is the diagnosis.

CVI can cause the same difficulties as DCD. A child may be diagnosed with DCD before CVI was identified (see Labels - Incorrect?). We know people with CVI who previously had a DCD diagnosis, and we also know people with DCD who do not have CVI. Many different complex brain processes can create what looks like the same difficulties.
Further reading: CVI & DCD Paper

Developmental Delay
Developmental delay is a general term used when a person has not 'developed' in a way that would be considered age typical. 'Developed' could refer to almost anything, including their motor skills, communication abilities, understanding of language, social skills and learning levels. The term does not explain what the problems specifically are, so also cannot explain why there are difficulties, so it is an extremely broad term, which can be taken quite negatively by some to mean the person is a bit 'behind' others.

If the person has CVI and has been assessed as having a developmental delay, take this just as the first step, and look to understand what is delayed and why. Some activities may not be possible due to their CVI, this is not a delay - none of us can do the impossible! We know of many cases when a person understands that a visual impairment is responsible for difficulties, that this can be very empowering.

Note the word delay implies that it will be possible for an affected person to 'catch up', which may not always be the case, and so the term 'delay' may be being used inappropriately.

Further Reading
Lessons Level 2 How The Brain Learns
Access - How Do We Learn?

Dyscalculia is where a person has difficulties with numbers, that fall outside of the normal range of abilities for their age group. It is not simply a case of finding maths more difficult than others, although as would be expected, this is the outcome for many. Simple number challenges, like counting backwards, or ordering numbers from lowest to highest can be extremely difficult for affected people. This is a relatively newly described condition and the causes are unknown.

With CVI, the way numbers are taught, often using visual cues like counting the number of balls or birds on a picture card, can lead to confusion, because not everything is always visible, and so the numbers may not make sense. If the early learning of the basic concept of numbers does not make sense, everything based on numbers is going to be difficult.

Using touch rather than vision, for example an abacus, plus counting fingers and thumbs and toes, can help with the early learning of numbers. For multiplication, the old fashioned repeating the times tables in chants or songs can help memorise them. Avoid cluttered pages with too many crowded numbers.

Further reading: Lesson 12a Dyscalculia

Dysgraphia relates to difficulties specifically around writing. It can be due to poor fine motor skills, poor spacing on the paper, so written lines are uneven and words can run over each other or have gaps that are too wide, with poor spelling. Many combine reading and writing difficulties under the condition dyslexia (see below).

With CVI, optic ataxia which is common in people with CVI, can cause the difficulties with handwriting that does not seem to be controlled or neat.

Further reading: John's Writing Storyboard.

It was an eye surgeon (German ophthalmologist Rudolf Berlin) who came up with the term dyslexia. Patients had difficulty reading when their eyes were fine, so he surmised that it must be to do with how the words were being visually processed in the brain. From the 1870s when the discovery was made, until the 1950s, dyslexia was considered to be a visual processing difficulty affecting reading. In the 1950s, new ideas about phonetic causes emerged, and for the following sixty years, the cause of dyslexia was considered to be phonetic, not visual. Current thinking identifies many different causes of dyslexia, including both visual and phonetic processing.

CVI can affect reading and writing in many different ways, including not all of the words being visible, losing words, not being able to learn to recognise letters and words, not being able to read due to visual crowding and writing difficulties because of inaccurate guidance of reach (meaning the pencil does not go where it is meant to.

CVI is a known cause of dyslexia, but this applies only to people who have typical language skills.

This is complicated, because if the person has delayed reading and writing skills, and delayed language skills, all due to CVI, then they do not have dyslexia. The reason is because they would be considered to have an overall learning disability, which would account for their reading and writing difficulties.

This is where labels become confusing and difficult and you need to refocus on the person. If they have CVI and reading and writing are difficult, then look at approaches that match their specific reading difficulties, that may help them.

Further reading:
Newsletter 18 CVI & Literacy (with links to all our other related resources).
Lesson 12b Neurological Dyslexia

"Dyspraxia is an enigma" (quote from link below). It is widely used to mean problems with movement, but there is no agreement on a definition, or even terminology. That does not mean the difficulties people who have been told they are dyspraxia have, are not genuine difficulties.

The problem with dyspraxia is this lack of agreement as to what exactly it is. The beginning of the journey for this label, started with an observation, that was given a name, 'clumsy child syndrome'. Quite correctly the negative connotations gave rise to a new name, dyspraxia, but there was no agreement as to what it is, or even what it relates to, some thinking it is a learning difficulty , others suggesting it is linked to autism. Next comes Developmental Coordination Disorder (DCD, above). A recognised medical condition with agreed diagnostic criteria. We use the term DCD for this reason. Dyspraxia may not be an incorrect label but it tends to not be specific. As with all labels, as we learn more, our knowledge grows and we are able to improve on what we did before, sometimes with a new name.

For CVI, please see DCD (above).

Further reading Dyspraxia or developmental coordination disorder? Unravelling the enigma (paper)

Face Blindness
Brain injury affecting the right temporal lobe causes a form of CVI leading to facial recognition difficulties. This facial recognition difficulty, or face blindness, is called prosopagnosia (Greek: Prosopos=Face a=not gnosis=knowing). This form of CVI can vary in severity from being complete to partial, and in many who are affected, can also cause inability to see the language of facial expression.

Prosopagnosia can also occur on its own from birth. This condition, is thought to affect nearly 3% of the population in various ways, where a person can see a face very clearly, down to being able to count freckles or eye lashes, but is unable to match who they are looking at with a face in their memory of faces (probably in their right temporal lobe). This is not a memory problem. Research has shown that this part of their brain is processing typically, so it seems to be a 'matching' issue, where the brain is not able to put the two things together (the face in the mind and the face the person is looking at) and match them as the same. This form of prosopagnosia is not classified as a cerebral visual impairment.

Further reading Lessons Level 8b Impaired Facial Recognition

Global Developmental Delay (GDD)
Where the term Global Developmental Delay is used, this means that the difficulties are across the whole of development. In practice, this means that many, or more than one area of development is either delayed or not typical. Difficulties across many areas can all get very muddled, and you need to help separate what is causing difficulties and why, to try to match the support for the person. Foe this term the word 'delay' is arguably not a good choice, because affected people may not necessarily catch up.
See Developmental Delay, above.

Intellectual Disability
Intellectual Disability was previously called Mental Retardation. Intellect refers to our ability to reason and understand things. With intellectual disabilities, the measure is against a person with typical intellect, which is measured with a test called the Intelligence Quotient (IQ). It is increasingly widely accepted that IQ is just one of many important measures of a person's abilities, and does not include areas like social skills which are needed for development. Sometimes the term Intellectual Disability is used to mean a wider range of difficulties. Broader terms like Developmental Delay (above) may be used instead of Intellectual Disability.

Learning Difficulties / Learning Delay
Typically used specifically around school subjects.
See Developmental Delay, above.

Low Self-Esteem
Low self-esteem is common in people with CVI, and if not supported, could lead to more serious mental health conditions at they get older, see Mental Health Conditions, below. CVI affects the person's ability to learn the non-verbal language of emotions, affecting social development, in turn this may affect social relationships, and can lead to feelings of loneliness, unworthiness and a lack of confidence. The person may start to avoid social situations. They need help. See also Social Communication Difficulties, below.

Further reading
Learning Emotions with CVI
Lesson 8b Impaired Facial Recognition
Lesson 8c Impaired Recognition of Facial Expressions

Low Vision & Learning Delay
This term is often used in education to separate those children with visual impairments who are more able learners, from those who need more support. Low vision could mean due to the eyes, or brain, or both. Learning delay could mean almost anything, see Developmental Delay, above. The term may seem unfair, but it is used to help direct resources. A visually impaired child who is working towards exams to go to University and a child who may only speak a few words and is learning to hold a cup need different approaches and support - BUT both need approaches and support matched to their known difficulties. Low Vision & Learning Delay is an extremely broad term, and support needs to be tailored to the needs of the individual person.

Mental Health Conditions
It is not surprising that a condition like CVI that can affect social relationships, learning, behaviour and development, can lead to mental health conditions, and we know many people with CVI who have been affected by Depression. For many, conditions develop as difficulties become greater. Understanding how impaired vision has caused difficulties can be very empowering, and a pathway to help and recovery can be developed, matching strategies to the known difficulties CVI creates. For Mental Health support, please contact your local provider. Click here for UK NHS resources on Mental Health.

Multiple Disabilities with a Visual Impairment (MDVI)
As with Low Vision and Learning Delay, above, the term MDVI is used to separate those with visual impairments with many needs, from those more able. The term is also used to separate those with multiple disabilities with a visual impairment, from those with multiple disabilities but do not have a visual impairment. The term multiple disabilities may be mistakenly understood to mean multiple medical conditions, which may be the case, but the term is typically used to describe a person with a combination of medical and learning / developmental challenges. The purpose of this term is to help target support, as people who do not have visual impairments will benefit from a different teaching and support approach to those who do. Visual impairment can mean disorders of the eyes, brain or both, and anything from moderate visual impairment to total blindness. Support needs to be individualised and targeted.

Neurological Impairment
This is a broad term used to mean difficulties are due to a brain disorder. You need to know what the difficulties are and what is causing them.

Neurological Visual Impairment
Some use this as an alternative to cerebral visual impairment, because the cerebrum is not the only part of the brain that is responsible for the visual difficulties that come under the current CVI umbrella. Maybe simply 'brain based visual impairment' will be used in the future. It is all part of the evolution of the labels around this condition that we explained in our introduction, and is a good sign that we are still learning and expanding our knowledge base and understanding.

Means without words. The person neither speaks or shows any understanding of language.

CVI can profoundly affect the learning of language, and is key for development, so it is not surprising that non-verbal people have considerable learning challenges. CVI can be a major cause of these difficulties. With CVI, language may not be learnt, because it has not been made learnable by matching it to the way the person is perceiving the world.

Further reading:
Shopping for CVI Suggestions, Non-Verbal Children (Introduction)
Language (for Non Verbal Children with CVI)

Obsessive Compulsive Disorder (OCD) / Obsessive Behaviours
OCD is a diagnosable medical condition where a person feels unable to control a compulsion to do things repeatedly or organise things is a very rigid way. There are many on-line resources about OCD including from the UKs NHS Website, click here.

Many with CVI struggle to find things. The challenges of visual search are common and consistently recorded. To help people with CVI find things, they need them to stay where they are, so they can remember where to find them (because looking is difficult). This can lead to the person becoming very particular about things not being moved, to the point where the behaviour may be considered obsessive. This is different from the condition OCD, although potentially could lead to it over time, however we are unaware of any such recorded cases at present.

Profound Multiple Learning Disabilities (PMLD)
PMLD is another term to separate the most severely learning delayed from others with learning delays, so that support can be matched. The person may or may not have a visual impairment. Anything that means learning is severely affected can be included in this group. PMLD indicates a severe level of need, but little more as the subject is so vast. Click here for more information on PMLD from UKs NHS.
See also Developmental Delay and Global Developmental Delay, above.

See Face Blindness, above.

Sensory Processing Disorder
Previously called Sensory Integration Dysfunction, and relates to a wide range of difficulties linked to the senses. The range of difficulties is vast, as everything we experience is through the senses, so potentially anything that is difficult could be understood in terms of a sensory processing disorder. As is it not a diagnosable medical condition, there is no consensus as to the criteria, symptoms or definition. It can include difficulties with sounds, or the feel of anything, including the fabric of clothes in the skin.

CVI causes visual processing difficulties, and from many reports, also auditory processing difficulties. Many people with CVI are both tactile and taste averse, and the causes of these aversions can be explained due to their CVI. CVI is not considered to be a sensory processing disorder, although it does cause sensory processing difficulties. Some people identified as having a sensory processing disorder may have CVI, others may have autism (see Autism, above), or causes that are not known.

Sensory Processing Difficulties
This is a general term meaning that the challenges a person may face, could be due to how the brain is processing information received from the senses. All the incoming information to the brain comes via the senses, so you really need a bit more information, as all it essentially means is that the difficulties are due to how the brain processes the incoming information from the senses, which is not specific enough to mean much.

Social Communication Difficulties
This is a term used where a persond may have some difficulties with friendships and relationships, but not to the extent that the person meets the criteria for autism. It may be the difficulties are only mild, or the person may not have other challenges associated with autism.

CVI causes social communication difficulties for many reasons. Difficulty recognising people and understanding non-verbal emotional communications, for example through facial expressions, can mean the complex world of rules of social engagement are difficult to learn and understand.

Further reading
Learning Emotions with CVI
Lesson 8b Impaired facial Recognition
Lesson 8c Impaired Recognition of Facial Expressions

Speech & Language Delay / Speech Delay
A speech delay (called alalia) refers to the actual talking / speaking bit of language which requires the use of the lungs, vocal chords, tongue and teeth. Speaking also requires an understanding of language, which for most comes from hearing words, so that the sounds can be remembered and repeated. Most children pick this up over their first year and start speaking around the age of one. There are many on-line resources on speech delays.

Language is both in your mind (receptive) and spoken (expressive). Language delay is a very complicated area. Some people with language delays have no other learning difficulties or underlying conditions. This is sometimes referred to as a Developmental Language Disorder (click here for more information from the UKs RCSLT).

CVI can affect the process of learning language in many different ways, and in some people profoundly, so that they learn no language (see Non-Verbal, above). The language delay CVI causes, can create subsequent learning difficulties. Learning and language very much work together and need each other. Language is not just about talking, or even just about communicating. Language is a key part of learning as it provides a framework for knowledge, understanding and imagination. With CVI, language can also be a key part of learning to look and use vision in a helpful and constructive way.

Further reading
Lesson 2h Recognition (explaining language in the mind used to label what is recognised, a key part of the learning process for all of us)
Language (for Non Verbal Children with CVI)

Stimming is short for self-stimulating behaviour, and is commonly seen in autistic people who may repeatedly make the same movement, like waving a hand or tapping something over and over. The cause is not known, the purpose is not known, and whether the person has any control over the behaviour is not known. This means the view that it is a 'self-stimulation behaviour' is not correct, and for this reason the term 'stimming' is not widely used. It is an observation of repetitive body movements, that is all we really know at present, although there are many theories.

In CVI we have seen repetitive body movements, including head turning from side to side, sometimes when a person is excited about something visual. In our experience it can also sometimes be a way of seeing more when the area of vision seen (field of vision) is very narrow. Also rocking, which we know can help stimulate vision by creating movement.

Visual Perception Difficulties / Visual Processing Difficulties
These terms are used when vision has been assessed or observed as not processing typically, which is not due to any issues with the eyes. In all people, particularly with any sort of learning difficulties, it is essential that eye health and vision are regularly tested, as many have unmet visual support needs, usually requiring glasses. An unmet need for glasses can cause what looks like visual perception difficulties, because things that one might expect a person to see, they don't or can't see - because they need glasses!

Visual perception difficulties are where there are no issues with eye sight (or these have been accommodated or accounted for) and yet there are still issues with vision, meaning it is a brain and not an eye issue.

Many different things can cause visual processing difficulties, including certain medications, tiredness and stress. CVI also causes visual perception difficulties. As CVI is a medical condition, it can't be diagnosed as the cause without a medical (doctor) assessment. If you suspect visual perception difficulties may be caused by CVI, try some of the suggestions and if they work, learn a bit more, and it continues to work, then you are successfully treating the difficulties (see further reading, below).

Further reading Eyecare & Behaviour Improvements in Special Schools

Visual Fatigue
This is a condition of the eyes, where vision can be reduced when the eyes are tired. It is the same way leg muscles tighten if you walk too much. It is your body's way of telling your brain (so you!) that you need to rest.

Separately, we have observed that people with CVI can tire extremely quickly when undertaking certain tasks that require a lot of visual processing. Just moving from one class to another at school might be all it takes. Sometimes a person can tire in minutes, even seconds. As they tire, their visual processing capacity can rapidly and markedly diminish, in severe cases leaving the person functionally blind. This is not just visual fatigue, but is something we believe needs more research and understanding.

Visual Stress
Visual stress is where, what you are looking at, often if there is a lot of detail, becomes unclear, is sometimes described as fuzzy. It has been associated with dyslexia because looking at lots of words on a page can create visual stress, even though the eyes are working typically, but when there is less detail to process, visual information is seen clearly. Whilst visual stress is a visual processing difficulty, it is not considered a cerebral visual impairment.

CVI can create difficulties where there is a lot of visual information to process too, including difficulties reading when there are lots of words, but for different reasons.

Working Memory / Short Team Memory Difficulties
Your working memory is your short term memory. As you read this sentence, the end of it will still makes sense, because you can link it to the beginning, because of your short term memory. When you go to a room to get your keys, it is your short term memory that keeps that purpose in the front of your mind, so you know what you went into the room for. And when you go into a room and think 'what was I looking for?' it is your short term memory that has let you down. It is quite different from your long term memory which is more like a great library in your mind of everything you know.

Where short term memory is not working so well, you can look forgetful, distracted and make mistakes. It can look like many other difficulties. It can have many different causes, particularly poor sleep.

A part of the brain called the hippocampus is key for short term memories. A group commonly affected by short term memory loss are children who were born prematurely, children who were affected by complications at birth affecting blood flow to the brain, or very low sugar levels (hypoglycaemia). Research has shown this group have a higher than average rate of damage to the hippocampus. This group also has the highest proportion of children with CVI.

Further reading Lesson 2g Memory

See also Newsletter 24 introducing this section.


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At CVI Scotland we are devoted to helping people understand cerebral visual impairments, and together working towards developing the understanding of this complex condition.