Could my child have cerebral visual impairment?

Professor Gordon N Dutton MD, FRCS Ed Hon, FRCOphth

Children’s Vision Consultant

Emeritus Professor of Vision Science, Glasgow Caledonian University

Honorary Senior Research Fellow, University of Glasgow

Cerebral visual impairment (CVI) is the commonest cause of visual impairment in the developed world. A large part of the brain is devoted to seeing, so it is not surprising that conditions that affect the structure or function of the brain can interfere with vision [1].

The front of the brain ‘thinks’ ‘understands’ and ‘behaves’, the middle ‘feels and moves the body as well as hearing and understanding language’, and the back ‘sees’.

The picture made by the eyes is sent to the back of the brain where it is sorted out in different ways:

1. Processing the picture

First, at the back of the brain (the occipital lobes) the detail of the picture is sorted (measured as visual acuity). Seeing colour, handling the number of shades of grey that can be seen (contrast sensitivity), knowing the extent of the picture, (the visual fields), and dealing with the speed and direction of moving images are all processed in this area.

2. Guiding our movement and seeing lots of things at once

Second, at the top of the brain at the back (the posterior parietal lobes), there is an amazing system. The visual information is carried there from the occipital lobes by a connecting pathway, called the dorsal stream. For every moment of our waking lives, this area of the brain uses the incoming moving picture to guide our movements.

Reach out and pick something up. You ‘know’ that the picture is out in front of you, but it isn’t really is it? It’s inside your brain! What is amazing is that the picture out there in front is so compelling that you believe that it is there, but you are actually moving through the picture in your brain, fully expecting that it will coincide with the reality of the object you are about to pick up, which of course it is. This can take a while to get one’s head round, but it gets even more complicated. The whole process takes place completely unconsciously!

Some people who have gone blind in both eyes because of damage to the back of the brain, which spares the movement seeing centre, are able to accurately move through the world that they do not consciously see. Functional scans of the brain show that they do this with their intact posterior parietal lobes. “But wait a minute” you may be thinking, “I know what I can see; and I chose and knew what I picked up.” Yes, but the conscious seeing and knowing is performed separately by the closely interlinked bottom of the brain at the back, the temporal lobes, which are connected to the occipital lobes by another pathway called the ventral stream.

3. Recognition

This is the third part of the brain’s conscious visual processing system. The temporal lobes serve conscious vision and recognition.

You recognise a friend in a group of other people you don’t know. To do this, you have a memory store of all the people you know. In came the picture of the group of people. The pictures of all their faces were compared with your memory store and there was one match, - your friend. What an amazing bit of computing! This part of the brain also allows you to find your way around without getting lost.

4. Dealing with the cluttered scene

To be able to move through the visual scene, a number of things need to happen. The unconscious picture needs to be processed very quickly, it then needs to be held in automatic unconscious working memory for a short time, after which it needs to be shed. Otherwise the brain would quickly fill up with useless out-of-date information.

As many items as possible in the visual scene need to be available at the same time to let us move through a cluttered environment, and to let us choose where we go. This is done by the visual reference library in the temporal lobes giving conscious knowledge of what we are seeing, while the dorsal stream pathways are providing the RAM in the computer of the brain so that we can attend to a number of things at once, by linking to the front of the brain which makes the conscious choices of where to go and what to focus on.

The two visual analysis systems, the dorsal and ventral streams, are blended so well that they work together in harmony, but of course we are unaware of all the unconscious visual workings of the brain, and therefore believe, wrongly, that we have conscious awareness of everything that our brains are seeing and handling.

So how does this information help in finding out whether a child has cerebral visual impairment?

Any element of what has been described may not work so well. Even with the right glasses, children with cerebral visual impairment can have a range of visual difficulties, unique to themselves, due to any of the processes outlined not working so well, in any combination or severity. The table below gives a list of some of the difficulties due to cerebral visual impairment along with approaches that can be used to help.

Problem	Approaches
Reduced clarity of vision.	Enlarge text Double space text Present text in small sections. Reduce distractions Limit tiredness
Colour vision and contrast sensitivity impairment	Bright and clear educational material and toys. Distinct colour boundaries Good contrast
Lack of vision on one side	Tracing of text with a finger or ruler Turning text vertically or obliquely Appropriate seat position in classroom Turning of head to check the hemianopic side Careful guidance around new environments Training in crossing roads Turn plate to eat food
Lack of vision down below	As with hemianopia Regularly looking down to check the ground ahead Tactile guide to ground height
Impaired ability to move the eyes	Movement of the head Enlarging text Double spacing text Tracing of text with a finger or ruler
Impaired ability to see movement	Television programs with limited movement Educational material with limited movement Careful training or guidance in crossing roads.
Difficulty finding a toy in a toy box or an item of clothing in a pile or wardrobe	Separate storage of favourite items Organised storage systems Always store in same location Avoid clutter Colour coding and labels
Difficulty finding an object on a patterned background.	Use plain carpets, bedspreads and decoration.
Difficulty finding food on a plate	Avoid patterned plates Avoid sauces/ gravy Separate food portions
Problems seeing a distant object	Use zoom on video/ digital camera to view
Problems reading	Enlarge text Double space text Masking surrounding text Computer programs to present information
Difficulty finding someone in a group.	Wear obvious identifier Always stand in same location Waving Speak
Tendency to get lost	Training in seeking and identifying landmarks Visit new locations at quiet times
Problems with floor boundaries, steps, kerbs and uneven surfaces	Avoid patterned floor surfaces Bannister Mark edge of stairs Good lighting Tactile guides to gage the height of the ground Approach obstacles with “Look- Slow- Check- Go” Activities to improve coordination
Inaccurate visually guided reach	Reaching beyond an object to gather it Activities to improve coordination Occupational therapy
Difficulty ‘seeing’ when talking at the same time	Limit conversation when walking Identify obstacles by tactile stimulation
Frustration at being distracted	Limit distraction Minimise background clutter Minimise background activity. Quiet table at school
Difficulty recognising people and photographs	Introductions Training in identifying voices Consistent identifiers worn Training to recognise identifiers
Difficulty recognising shapes and objects	Training to identify and recognise identifiers Training in tactile recognition
Difficulty reading facial expression	Training in recognising facial expressions Expression of mood by tone of voice Explanation of mood in words
Getting lost in known places	Training in orientation. Encouraging leading Incorporating landmarks in Mnemonics /Poems
Difficulty in new environments	Training in orientation. Encourage exploration –Visit at quiet times –Hide and Seek –Treasure Hunts
Visual fatigue Prolonged visual processing	Minimise clutter Reduce distractions Reduce detail and complexity Well earned breaks
Social problems	Good understanding and support at school Identify problems and solutions Encourage child to overcome them Well known informed peer group Find activities child enjoys and can excel in

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One bitterly cold Friday in December well over a year ago, in Glasgow, Scotland, I was privileged to observe Gordon Dutton doing his characteristically thorough assessments of children at the Vision Clinic in the Royal Hospital for Sick Children, just weeks before he retired from that post. It was an occasion I am not likely to forget as he patiently quizzed parents about the child's history and tested the child's vision with tools he has developed over the years. Gordon has been leading the field of cerebral visual impairment for some years now. He is a prolific writer on the subject and we look forward with great interest to his new book for teachers on CVI. He has been an enormous inspiration to many in recent years, myself included. Many thanks, Gordon, for submitting this article on such a vital and under-resourced topic.     - Maurice

Gordon N Dutton