Paper: Higher Visual Function Deficits in Children with Cerebral Visual Impairment and Good Visual Acuity, Arvind Chandna et al, link at end of page.
Our introduction to this paper is a little longer than usual because a number of important issues concerning CVI are raised.
Cerebral Visual Impairment (CVI) is the umbrella term for a group of many different brain based impairments of vision.
In the past, children most commonly identified as having CVI had reduced visual acuity, meaning they could not see detail clearly, and / or visual field loss. Measuring visual acuity usually involves charts with black letters or shapes on a white background, but how we use our vision every day is much more complicated, and also involves colours and crowding, shapes and movement and much more. A near typical visual acuity measurement, does not necessarily mean the child does not have other visual difficulties.
Research we have shared, from the CVI Project in particular, shows that using diagnostic criteria that must include reduced visual acuity, means the vast majority of children affected by CVI, most of whom struggle with learning, remain unidentified and undiagnosed, meaning their challenges are inadequately supported.
The majority of children likely affected by CVI have typical visual acuity, but other CVIs are present. In this paper these are referred to as Higher Visual Function Deficits (abbreviated to HVFDs), also known as Higher Visual Processing Deficits (HVPDs).
Higher Visual Function Deficits
Vision is a process, starting with the information your eyes receive from what is around you and ending with your conscious awareness and understanding of what you are looking at. That final part is what you are making sense of right now as you read these words, and it is the only part you are aware of; it is sometimes referred to as 'frontal' because it is being consciously processed in the frontal lobes of your brain.
The two diagrams below show the process from the eyes to what you are aware of visually, one very simple, the other more detailed.
CVI where visual acuity is reduced and / or there is visual field loss, relates to an area of processing deficits called occipital, because these are disorders processed in the occipital lobes. Issues with colour and contrast sensitivity also come under the area of occipital lobe processing deficits.
Going higher up the tree, we reach the dorsal and ventral processes.
In addition to creating the picture of what you are looking at, the brain performs many other visual processes, all at the same time, so you can, for example:
These come higher up the order, and when not working typically are broadly in the areas of dorsal and ventral stream dysfunction. This is also explained on our page Perceptual Visual Dysfunction (PVD) Paper.
This is where the name Higher Visual Function Deficits comes from, because they are, very simply, functions that are higher up in the processing order, and not working so well, and so, deficits.
There is a very important concept to remember when it comes to higher visual processing deficits, that they are non-conscious.
The vast majority of tasks your brain does are processes you are not aware of. When the higher visual processes are not working typically, the person is not aware of this. The only thing they will be aware of is things being difficult, usually without explanation. Meaning, from the child's perspective going back to our list above...
Without explanation or understanding why the child is having difficulties, in many cases we know, the child, and regrettably others around them, very often end up believing the fault lies with the child, they must be:
It is not the child's fault.
This is why the work described this paper is so incredibly important.
The child with higher visual processing deficits has a non-conscious condition. The affected child may be incredibly articulate, but none of us can explain something we are unaware of. The child can be disabled in many ways by their visual perceptual difficulties.
Children's higher visual processing difficulties we know have been attributed to general learning difficulties, dyslexia, autism, ADHD and other labels affecting learning, development, behaviour and social communication. This makes the challenge of identifying affected children, to ensure their optimal support, particularly difficult because
Where the child had reduced visual acuity, this would in many cases have been picked up, but we are learning that the majority of children with higher cerebral visual impairments have typical or near typical visual acuities, so the purpose of this research was to find out how effective a set of carefully chosen history taking questions can be in detecting affected young people.
But, there's another complication...
Research on the complexities of finding and diagnosing these children requires children to be already diagnosed, so we have a chicken and egg problem.
So, finding the way to identify such children can be difficult.
The research described in this paper is called a prospective study. Prospective means looking ahead, a bit like the old 'prospectors' who went searching for gold. Whilst all research needs a theory to test, this research is very much about looking ahead to see what could be found out, hopefully to find a way to help identify these children.
Those taking part in this research were:
This research centred on a set of 51 questions called the CVI Inventory.
The CVI Inventory
The CVI Inventory is a set of questions designed for children who already have a CVI diagnosis, to understand more about which particular visual processes are creating difficulties, because with CVI, many different cerebral visual impairments can cause the same difficulty, but require different methods of support, for example knocking a glass over ...
All of these reasons why a child might knock over a glass need different approaches. The issue is not just about knocking over glasses; pretty much everything that happens to a child across their whole day if they have CVI will be affected in one way or another. To ensure support is targeted to their individual needs, a way to separate, or discriminate what is and is not causing the difficulties is needed, and that was the original purpose of the CVI Inventory, to do just that.
So, the CVI Inventory was not designed to be a diagnostic or even a screening tool. It was designed to be used to help professionals supporting a child with CVI better understand the nature of their difficulties, so that support can be improved by being targeted at the cause of the difficulties.
The purpose of the research described in this paper was specifically in relation to children with higher visual processing deficits, who had typical visual acuities, to find out whether the questions in the list were effective in identifying children with higher visual processing deficits, and if so to find out which would turn out to be the most effective questions in doing so. So, very simply, to find out if it still works when used this way, and if some questions were better than others. This knowledge could then be used to improve identification of affected children by using the best questions.
Due to this different purpose, the very specific group of children with CVI studied, and other changes, the name was changed from CVI Inventory to Higher Visual Function Question Inventory, abbreviated to HVFQI in the paper.
What makes a good question?
The purpose of the inventory is to separate children who do have the higher visual processing CVIs from children who don't, and further, to identify and separate out the underlying nature of the visual processing deficits in those children who do have CVI.
Questions have a choice of answers with scores:
The best questions are those that are 'most discriminatory' which means they have the highest score difference between the children with CVI and the control group of children who have typical vision, and these were, in order (most effective questions highest):
Parents / Carers
Clearly, these questions have been designed for the parent or carer to address. The person closest to the child who knows them best. The parent or carer plays a critical and integral role in every part of their child's CVI, including identification, diagnosis and support.
The Top-11 Screening Questions
This paper suggests these eleven questions could be asked of parents of children at risk of having developed the higher visual function deficits of CVI as a time efficient way of identifying those affected. The authors urge caution as they further investigate whether these Top-11 questions are applicable to a wider group of children with CVI. Please see the end of this page - can you help with further research?
While the number of children with proven CVI studied (33) may be thought of as relatively small, the results were highly consistent. From a research point of view, the statistical analysis shows the results to be reliable.
A set of reliable screening questions does not make a diagnosis. A positive result raises a flag to suggest the child needs more investigation for a higher visual processing deficit and underlying CVI.
The question set described in the paper could well prove effective in identifying children with higher visual processing deficits, but this type of CVI is not well recognised, even though the numbers affected are likely to be considerable.
Currently it is clinicians who have taken the initiative to master the subject for themselves, who are able to detect and help affected children. So without wider dissemination of the information, for the vast majority of affected children, receiving a diagnosis is going to prove problematic.
As CVI is a medical diagnosis, in most countries a medical doctor is the only person entitled to give this diagnosis. This set of questions now needs to be tested on a new set of children at risk of being affected by higher visual function deficits to find out whether it will prove to be a useful identification tool.
Neither the CVI Inventory nor the Higher Visual Function Question Inventory alone are enough for a medical diagnosis.
Of the 33 children with diagnosed higher visual processing deficits, 31 had an MRI scan, 7 of whom had a normal scan. So in this set of affected young people, 23% of MRIs showed no detectable abnormalities.
This fits with previous research into children with diagnosed cerebral palsy, which has shown that 12% have normal MRIs.
As with all tests, there need to be checks for false negatives and false positives, where the result is incorrect. With MRIs, there is rarely a false positive, because the atypical view of the brain can be seen and measured. But clearly with MRIs, there can be false negatives, in which a brain that is processing atypically causing cerebral palsy, CVI or both, can look completely normal. For this reason, a typical MRI does not rule out CVI as the diagnosis.
Is it definitely CVI?
Yes. Even with a typical MRI and normal visual acuity, these higher visual processing deficits definitely come under the umbrella of CVI, based on decades of research, all making the same point, that:
Normal visual acuity and absence or presence of neuroimaging findings no longer excludes a diagnosis of CVI.
What name should be used?
This paper uses the term higher visual processing deficits. Another paper has used the term visual perception dysfunction. There are also the terms dorsal and ventral stream dysfunction. The purpose of these names is to distinguish this group of CVIs from the better known ones due to occipital lobe dysfunction. All of these names are correct, but it can be a little confusing. Where there are discussions around what terms to use, we think it is always important to think about how using such labels can make the child feel.
'Not Applicable' Questions
Many parents know how frustrating it can be when some questions are not relevant. This can sometimes be irritating or upsetting, like questions asking how your child manages going downstairs, when they use a wheelchair. As part of the research, the option to say 'not applicable' was included, with the purpose of making future sets of questions more relevant to the child.
Profoundly Disabled & Non Verbal Children
Most of these questions expect the child to have basic language and communication skills, for example
There is another group of children who have very limited language skills or are completely non-verbal, or the most profoundly learning disabled. Of these children in special schools, as many as a half may have undiagnosed higher visual processing deficits (click here for references). We all agree this is an area where work is urgently needed because identifying the deficits enables optimal care and teaching.
The eleven questions on the face of it look like they could be a very useful tool as part of a bigger toolkit, not the only tool necessary, and the researchers are very clear on this point and that further research is needed (see link below to help).
No single tool or process or protocol can possibly pick up every child or adult with CVI. Each is unique and multiple tools are needed by those who identify and diagnose CVI. Based on this research, and the accompanying growing research evidencing a large group of undiagnosed children with higher visual processing deficits, this tool could be extremely useful in identifying them.
We all need a CVI toolkit. For parents and carers, it is in relation to one child, their child. For different practitioners it is in relation to many different children.
These eleven questions are a potential great addition to the CVI toolkit as a possible screening tool.
Please can you help this research?
This important international research continues and the team are looking for adults and parents of children, from anywhere in the world, with a diagnosis of CVI, to help them. They will need up to an hour and a half of your time for a telephone or zoom interview which will include multiple choice questions.
Click here for more information on the project or email firstname.lastname@example.org to be a participant / get in touch. Thank you.
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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.