Cerebral or Cortical - Are they the same? Why does it matter?
One reason we think this matters is because there is a lot of confusion around these two terms. In this newsletter our aim is to clarify some of the areas people tell us they find difficult to understand.
The term cortical visual impairment came first. It was initially used as an umbrella term to describe impairment of the 'basic' (or lower) visual processes, including:
Reduced visual acuity
Reduced contrast sensitivity
Visual field impairment
Later, during the 1990s, researchers began to identify additional visual disabilities including impaired visual recognition and visual search, due to what became known as ventral and dorsal stream disorders, (or disorders of 'higher visual processing').
The cortex of the brain is the outer part, yet brain injuries tend to affect the inner white matter as well, so in many countries, the word cerebral was adopted in place of the word cortical, and the term cerebral visual impairment came into common use to cover all these different features
So in these countries the terms cortical and cerebral mean the same, but with the word cerebral having replaced the word cortical. It's a bit like tuberculosis was previously known as consumption (and King's Evil & Potts Disease!). As we learn more, sometimes names change to reflect that.
Some people use the terms cortical and cerebral as completely interchangeable, but others give these terms different meanings, and this is where people have reported difficulties understanding. This can lead to confusion, for example:
Q: When she was 2 years old my daughter Annie had a stroke affecting her primary visual cortex in the occipital lobes - I was told that cerebral visual impairment affects only higher visual processes. Does that mean she does not have a cerebral visual impairment?
A: As noted above, in most of the world, the more global term cerebral vision impairment would be used rather than cortical visual impairment. Some, especially in North America, do differentiate between cerebral and cortical. It is important to be sure that regardless of what C is being used, that the understanding of the person's strengths and weaknesses is well understood and that an appropriate plan is in place to address the needs of the particular child. The label should not limit one's ability to appropriately observe, assess and intervene to improve visual access to the child's environment. For this, an understanding of which CVIs the person is affected by is required.
Q: When people talk about the leading cause of visual impairment (in industrial countries) in children - is that cortical or cerebral or both?
A: Two of the main causes of CVI in children are premature birth and when oxygen to the brain has been limited (before, during or soon after birth, for various reasons). Here, the typically affected part of the brain can impair the higher visual processes, and in some the basic visual processes as well. It is relatively uncommon for children just to be affected by impaired basic visual processes. However, these are umbrella terms for many different visual impairments from the brain, that is why we, and many others, often use the abbreviation CVIs (plural) rather than CVI. Each child is affected differently, by one, some or many of the visual impairments, mildly to severely - the umbrella terms are of very limited value. In our opinion, both words (cerebral and cortical), as explained above, refer to the same group of conditions, and the distinction is essentially regional. Just like some say petrol and others say gas - they are the same thing.
So we ask again - does the name of the umbrella matter that much?
Let us put all the umbrellas to one side and think of it differently.
Imagine the brain is made up of buttons, like shirt buttons and trouser buttons of different shapes and sizes, all threaded and interwoven together, into a three dimensional button brain. It is estimated that 40% of all those buttons are needed for visual processing. But, the 40% aren't isolated, they are connected by threads to each other, as well as many of the other 60% which in turn connect and communicate with the rest of the body. These interconnections are where the estimate that 70-80% of learning is in some way visual, comes from. From all these connections with other parts of the brain.
Ask anyone with any expertise in the brain. Where such a large amount (40%) can be affected, the number of different combinations of types of difficulty is enormous. To help a person having difficulties, you need to establish which buttons are the problematic ones. So, for us, these umbrella terms are not especially useful when it comes to understanding and helping the individual. What we need to know is which connections or clusters of connections are causing the difficulties. Which CVIs?
Why? Because disorders of different buttons can lead to the same or similar difficulties, like problems finding things or recognising people. And different affected buttons require different approaches.
These buttons might be thought of as the anatomical part of the visual impairment, the actual bit of the brain that is not working typically. Is that important to understand how to best help the person? Of course - how is one to know what to do if one does not know what is wrong? This is where all of these umbrellas, including cerebral / cortical visual impairment, are of limited use.
Key, to assessing anyone with visual difficulties due to the brain, is firstly working out which visual impairments they are affected by. CVI (cerebral or cortical) is not the answer. Then, the person can be profiled and assessed, and the elements of their functional vision established. From this, a programme of support can be developed. Without understanding first, which of the visual impairments the person is affected by, we do not see how this could be possible.
Labels and umbrellas create confusion and difficulty, and move away from the affected person in the centre - it should all be about them. You will see from our list (link below) that one needs to know a great amount about them, which is why we think the parents and carers are the most important people in their support.
A few years ago here in the UK, market traders were in uproar because they were told they had to sell their apples in kilograms rather than pounds - but the apples did not change. Cerebral / cortical - does it really matter? Maybe it is time we just accepted their use interchangeably, like pounds and kilograms, different words essentially meaning the same thing.
The brain, like the apples, is unchanged by the different labels.
The CVI Scotland Team
PS Everything new can be found in our Updates section, and via Twitter @scotlandcvi and our Facebook page.
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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.