Functional Vision is about understanding what the person can see, to learn:
Note: Following on from this section is an explanation of some of the measurements you may have, including functional visual acuity and contrast sensitivity. This section is called The Technical Stuff.
Seeing clearly means seeing comfortably, and when necessary, quickly.
When you might read a book, you read it in a text size that is comfortable, and doesn't require you to strain and take a long time. If the text was half or a quarter the size in the book, you may still be able to read it, but it becomes more of a strain and takes longer, and with that some of the enjoyment is lost.
If a person's vision means that things need to be bigger to be seen clearly, you should not aim for the absolute minimum size they have shown they can see, you should aim for a size that would be comfortable for them to see, which will be bigger.
If a person has CVI it is likely that, for a range of reasons, what they can see clearly will vary. In understanding their functional vision, you will need to note detailed observations, as you did with the visual fields in the previous section. It is highly likely that the notes from observing the person's responses in various parts of their visual field, will be highly relevant to understanding their functional vision.
Observe the person and consider, once again
This time in relation to these three areas:
Consider all of the above in:
There are very few generalisations when it comes to CVI, but keeping the environment free from clutter is one of them. The visual brain is already challenged, and having to sift through clutter to see will make seeing clearly much more challenging, and in some cases not possible. It can also feel uncomfortable and this makes seeing more difficult.
How easy would it be for the person to find the letter A in both of these classrooms (above)?
An environment completely free of visual clutter has only one colour. A cheap and practical option could be using a tent in the home.
The tent and accessories all being a single colour is more important that the actual colour.
A small percentage of people with CVI will have a stronger visual response in low lighting conditions. Some people with CVI may find bright lighting very distracting. Through your observations note the optimal lighting conditions that help the person see objects most clearly and comfortably.
As your observations develop the highly personal and individual nature of the person's visual world should be emerging. These observations need to be part of the long term journey with the person. As they develop new skills or face new challenges these observations will provide the information that everyone can use to ensure their environment is always at its best for development opportunities.
The person is very unlikely to know how their visual world is altered compared to others, even highly intelligent articulate individuals.
The best environment is where a trusted dedicated person, with time and compassion, can tune-in to the person's visual world, and help explain the challenges. From this, strategies that are relevant to that person, and their developmental level, can be created.
From these observations you will:
For people with CVI, the functional visual acuity can seem to vary depending on a number of issues. An understanding of the person's visual acuity will lead you to further assess what factors seem to reduce the acuity level, and what conditions seem to enhance it. This information will help you understand more about the other cerebral visual impairments that may be affecting the individual, for example the ability to recognise, simultanagnosia or optic ataxia, fatigue, discomfort and mood.
The information will also help you to identify key factors that either help, or make things worse, for example feeling secure in a familiar place making vision work better, or feeling tired or hungry, noise, or a cluttered environment, making it work less well.
The (free) Peekaboo App is an accurate way of measuring visual acuity. Take a look at this very short film:
If you are in the UK and have access to an iPad, this is a great free app you can download to test visual acuity, which is especially helpful for very young and more complex people (although would work on anyone). It is not available on phones (because the screen has to be big enough for the test) or computers.
With very young or more complex children who are unable to point or reach out, you can learn to observe by watching their eye movement (as the film demonstrates). This in its own right is a hugely beneficial thing to learn, even without the test for acuity. Learning to confidently understand what the person with CVI is looking at, and equally importantly is not looking at, is the first step in learning to understand their visual world.
Because Peekaboo is a free app, and also a fun app, it can be used over and over. You will become more confident, but also learn more about the person's vision. If they are straining to see one of the targets, or take longer to see it, they may be showing you that it is possible but difficult. You are looking to understand 'comfortable' vision, just like you wouldn't comfortably read a book with the tiniest text you could just make out (it would be a strain). You will learn a measured acuity, which can be shared with the professionals supporting the person. Key is to know quite simply how big something has to be to be seen.
Connor's mother who has tested the app writes:
"It literally took two turns for Connor to 'get' the 'game' as to him it is a game not a test. I thought it would be too complicated for him to understand but it has clearly been designed with very complex children like Connor, who have previously proved difficult to test, in mind. Connor does not have the dexterity to point and touch the target, although he tried to reach. What was interesting was how obvious his eye movements were. This is something I have tried to observe in the past, but because he thrashes his head from left to right, particularly when he is seemingly 'looking' at something, this has always been really hard. I think with Connor it will be useful with repeated use rather than just one use. As he becomes more familiar with the game, he will become more confident and faster, and this is when we will really learn what he does see, what he doesn't see and what he strains to see."
Once you are confident about what the person can see, the next step is to make things big enough, and then to understand when they don't see. Where something is big enough to be seen but not seen points towards other causes, for example simultanagnosia.
The ideal relationship for everyone, particularly the person with CVI, involves the family working together closely, and with the harmonious support of professionals.
Everyone's aim should be to optimise the potential for the individual by making sure that the person can perceive, understand and learn.
As your understanding of the person's visual world develops you need to tell everyone how big everything has to be!
Not the minimum size things have to be, but a comfortable size that can be seen easily, without strain.
You are taking your understanding of the person's visual world, and using this to ensure that everyone who works with that person also understands their functional vision, that is:
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