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

-  -  -  -  -  -  -  -  -  -

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 

Tips on making texts & pictures accessible to a large print user

The following is directly applicable to those working with the student mentioned in the last few posts, who suffered vision loss due a brain tumour. But of course it can apply to many children with low vision. 


Enlarging texts, diagrams and pictures

1. NOT A3. When adapting texts it is not sufficient simply to enlarge an A4 sheet to A3 size as this rarely ensures the text is in his preferred font size. Besides the A3 sheet is bulky to handle and difficult to manipulate in a classroom.
2. 26 POINT. The pupil benefits from a font size of no less than 26 point. He may appear to read slightly smaller sizes but his speed of scanning is dramatically reduced as the text reduces in size.
3. ARIAL. The pupil benefits from a plain, unembellished font such as Arial and he prefers bold formatting. He can read other fonts but his ease of scanning may be affected with more complex fonts.
4. ADVANCE PLANNING. To ensure texts are adequately enlarged his reading materials should be presented to staff supporting him in adequate time for them to be adapted. Reasonable notice for adapting work is one week in advance of lessons.
5. ORIGINALS. Originals should be provided for adapting in preference to copies and where possible originals in colour.
6. QUALITY IMAGE. When adapting materials the quality of images and diagrams needs careful consideration. Enlarging a low resolution image can actually make it less accessible as the pixels become distorted with enlargement. Black and white images and diagrams may lose their definition if enlarged. High resolution images can be enlarged with no loss of quality. Alternatively pictures or diagrams may be made accessible in other ways. They can for instance be audio described by the teacher or support worker. Or instead of a picture descriptive text may be provided.
7. AUDIO DESCRIPTION. In addition to presenting images, either in print or projected on a board, the pupil benefits from audio description of those images. Visually impaired pupils always benefit from significant extra and enhanced verbal description and explanations of material that is not fully accessible.
8. NUMBERING LINES. Be precise when giving instructions. Giant print is difficult to navigate at the best of times, because of the limited number of words on the screen or page. Therefore clear precise instructions from the class teacher will help the pupil to navigate a page of writing and find the right line or word when attempting to move from one section to another quickly. Numbering pages, paragraphs or lines may help the pupil to find the location of a text more quickly and effectively. 
9. PACING. The pupil will benefit from attention to the general pace of lessons and especially verbal description of board texts and graphics. A rapid lesson pace may not be suitable for the pupil especially where texts are involved. His speed of scanning texts is slow compared to other pupils and it may take him a while to coordinate his vision and writing. Slowing the pace a little to match the pupil’s speed of access will aid the pupil keep up with lesson content.
10. COLOUR CODING. Colour coding of headings and key points will enable the pupil to navigate a page more effectively.

Vision Loss due to a Brain Tumour - 3. Pros & Cons of Assistive Equipment

Hi this is another episode relating to my student in year 11 secondary school. Mohammed, you recall, had a brain tumour and is registered blind as a result. The impact on a sighted young person of losing their vision is very different in many ways to someone who has grown up with a sight loss. There are all the visual memories for instance that he or she can draw upon, which is a major advantage when navigating through the environment. Mohammed is really a delight to work with. He is so positive and enthusiastic about using any bits of equipment that I bring in. And he is really keen to test drive hardware and software. In this short video Mohammed talks about the pros and cons of assistive technology – as I would call it – but you and he might just call it ‘gadgetry’. He now has a range of equipment from an ipad to a MYReader2 ‘CCTV’.

Equipment is useful but not the whole answer. It can help a person become independent but there is no one size fits all solution to a visual impairment. However that said I am excited by the new 'gadgets' that are being developed. The main con is their cost; they can often be highly over-priced for the average user and fortunately for Mohammed the education authority is still able to fund much of his equipment. Another con is that, like all technology, they become outdated very quickly. However this is where software has strengths, since it can be easily updated. 

A young person like Mohammed takes to equipment so readily I think because it really does make a difference. I was delighted how useful the MaxTV television specs were. Mohammed asked me early on if there was something to make the TV more accessible. These specs really do the job. He can now watch football on the TV without having to get close and block the screen for others. It may be useful in future blogs to focus on particular devices and review their pros and cons. So watch this space and add your comments as always. 

Vision Impaired due to a Brain Tumour - 2. What Mohammed sees

We’ll continue this video presentation of Mohammed with some comments on how he now sees the world after his operation. Mohammed had a brain tumour and after a stay in hospital and several operations his eyesight is severely reduced.  Only he can explain exactly how he sees, so I have asked him to describe how he now sees the world. The difference between Mohammed and many young people with visual impairments, of course, is that he has a very large memory of what the world should look like and he can compare what he sees now with what it was like. 

Mohammed tells us that his vision was normal but now as a result of his brain tumour he has severely restricted vision. All aspects of his vision are now affected: central detailed vision so vital for rapid scanning of the world and all that is in it, distance vision and being able to recognise people and watch the television and colour vision. 

Mohammed has lost the vision in his right eye and 50% of the vision in his left eye. In addition his vision fluctuates and he cannot see clearly beyond one metre. He cannot identify a face and he needs giant print size to be able to read.

He says it is like looking through a frosted window; it is blurry and unclear.

Mohammed cannot read normal print. He needs print in 26 point Arial font in bold formatting. Obviously this size print is not easy to produce as a rule in school and a lot of thought needs to go into how exactly this size and quality of print is to be produced for Mohammed.

Note that just by looking at Mohammed's eyes you would NOT think he has a visual impairment. His eyes look normal. The damage is in the brain hidden away from sight. That itself can create difficulties, because people who do not know him might think he can see when he cannot. 

Thank you Mohammed for these insights you have allowed us to have through your very lucid explanations. 

Vision Impaired due to a Brain Tumour - 1. The Trauma of Sudden Sight Loss

Whilst in the midst of his GCSE exams Mohammed was diagnosed with a brain tumour and had to have a lengthy stay in hospital during which he had extensive surgery to have the tumour removed. After the treatment he was left with severely impaired vision and the loss of his hormonal system. The implications for his academic life, his social life and his personal expectations for the future have been far-reaching and significant. He was kind enough to share his experience this week, with his parents' permission, so that others may become aware of what it is like and so that his teachers may appreciate the extent of the modifications and changes that will have to be made to accommodate his needs. In this short clip he introduces himself and tells us briefly about what happened. 

In this next extract Mohammed talks about how traumatic this was: the shock of suddenly losing his sight and how difficult it was being hospitalised for such a long period. To wake up and find that suddenly you can see nothing - it is impossible to imagine what that must be like. Added to this was the awful discovery that the tumour had destroyed his pituitary gland and that for the rest of his life he would be dependent on drugs to control his hormones. I believe it is important for us to see this and to be aware of how it affected (and still affects) Mohammed. None of us can begin to imagine what this must be like. We all take our health for granted. We take so much for granted: being able to live life independently without having to have things done for you; looking forward to the future and all that it holds. 

I hope that as you watch this video, and the others following, it will help us to see a little of what life is now like for this young man. Those who work with Mohammed will attempt to do their very best to assist him through this difficult time. But I believe the key thing is knowledge - i.e. to be aware of what he really needs - especially in school, where he spends a large degree of his time. All who have anything to do with our friend need to know precisely how and what he sees and what helps him the most. I hope this blog post will help towards this end. 

Retinal implants or bionic eye?

Record producer Robin Millar started losing his sight in the mid 1980s as a result of retinitis pigmentosa.

The condition resulted in the loss of the photo-receptor cells at the back of the eye, leaving him completely blind.

Mr Millar is one of two British patients to have a electronic retinal implant fitted, which sends electrical impulses to the retina. They then have to be interpreted by the brain.

His surgery was carried out at King's College Hospital, London.

He showed the BBC's Medical Correspondent Fergus Walsh how it works.

Retinal Implants offer hope to visually impaired

The bionic eye and how it works 

4th May 2012 UK

Two British men who have been totally blind for many years have had part of their vision restored after surgery to fit pioneering eye implants.

They are able to perceive light and even some shapes from the devices which were fitted behind the retina.

The men are part of a clinical trial carried out at the Oxford Eye Hospital and King's College Hospital in London.

Professor Robert MacLaren and Mr Tim Jackson are leading the trial.

The two patients, Chris James and Robin Millar, lost their vision due to a condition known as retinitis pigmentosa, where the photoreceptor cells at the back of the eye gradually cease to function.

The wafer-thin, 3mm square microelectronic chip has 1,500 light-sensitive pixels which take over the function of the photoreceptor rods and cones.

The surgery involves placing it behind the retina from where a fine cable runs to a control unit under the skin behind the ear.

Continue reading the main story

“Start Quote

I am able to make out a curve or a straight line close-up but I find things at distance more difficult. ”

Chris JamesPatient

'Magic moment'

When light enters the eye and reaches the chip it stimulates the pixels which sends electronic signals to the optic nerve and from there to the brain.

The chip can have its sensitivity altered via an external power unit which connects to the chip via a magnetic disc on the scalp.

Chris James from Wroughton in Wiltshire said there was a "magic moment" when the implant was switched on for the first time and he saw flashing lights - showing that the device was functional.

"I am able to make out a curve or a straight line close-up but I find things at distance more difficult. It is still early days as I have to learn to interpret the signals being sent to my brain from the chip."

Mr James, a motor-racing enthusiast, says his ambition is to be able to make out the silhouettes of different cars on the race-track.

Prof MacLaren, who fitted the first implant in the UK at the Oxford Eye Hospital, said:

"It's the first time that British patients who were completely blind have been able to see something.

"In previous studies of restorative vision involving stem cells and other treatments, patients always had some residual sight.

"Here the patients had no light perception at all but the implant reactivated their retina after more than a decade."

The chip results in the brain receiving flashes of light rather than conventional vision - and it is in black and white rather than colour.

Colour vision

But in an unexpected development, the other British man to have the implant says he is now able to dream in colour for the first time in 25 years. Robin Millar says he is also able to stand in a room and detect light coming through windows.

Prof MacLaren said the results might not seem extraordinary to the sighted, but for a totally blind person to be able to orientate themselves in a room, and perhaps know where the doors and windows are, would be "extremely useful" and of practical help.

In 2010 a Finnish man who received the experimental chip was able to identify letters, but his implant worked only in a laboratory setting, whereas the British men's devices are portable. The implant was developed by a German company, Retina Implant AG.

'Pioneering'

Mr Tim Jackson, eye surgeon at King's College Hospital who has also fitted one of the devices, said:

"This pioneering treatment is at an early stage of development, but it is an important and exciting step forward, and may ultimately lead to a much improved quality of life for people who have lost their sight from retinitis pigmentosa.

"Most of the people who receive this treatment have lost their vision for many years, if not decades. The impact of them seeing again, even if it is not normal vision, can be profound, and at times quite moving."

Both surgeons stress that the chip is not a treatment but part of a clinical trial. Up to a dozen British patients will be fitted with the implants.

Although it could ultimately benefit patients with the most common form of progressive blindness, age-related macular degeneration, they are not eligible for the study at present.

Nor are patients with glaucoma or optic nerve disease.

Nick Astbury, Chair of VISION 2020 UK, a global initiative for the elimination of avoidable blindness said: "This trial will bring hope to two million blind and partially-sighted people living in the UK. It is the first step on a long journey to help people with sight loss to see again and live independently".

BBC News 3rd may2012

http://www.robinmillar.org.uk/bionic_retina.htm

http://www.bbc.co.uk/news/health-17936704