Cerebral Visual Impairment

What is cerebral visual impairment?

Cerebral visual impairment (CVI) is a lifelong, brain-based visual impairment, caused by damage to the brain’s visual pathways or visual processing areas. The eye and the brain are a team and if there is a disconnect between the two, what we see and what we think don’t match up. This disconnect is what is happening in CVI. 

The eye is an anatomical extension of the brain, with multiple parallels between its neurons, vasculature, and immune response.

CVI is sometimes called cortical visual impairment or perceptual visual dysfunction.

While the eyes might be perfectly healthy and able to see, the brain has difficulty processing and understanding the signals they send. 

The disconnect between the light patterns coming into the eyes and what the brain interprets or “sees”, leads to a wide range of challenges in visual understanding, such as difficulties seeing fast moving objects, identifying objects below eye level and finding items in cluttered environments.

How common is cerebral visual impairment?

Recent research in the UK has suggested that brain-related vision problems could be more common than previously thought, potentially affecting one in every 30 primary school children. CVI is one of the most common causes of vision impairment in children in the UK and other developed countries.

What happens in the brain with cerebral visual impairment?

Seeing is a complex process that involves a partnership between your eyes and your brain. You can think of your eyes as windows that capture patterns of light from the world. These patterns are turned into electrical signals that travel along pathways to different parts of your brain. The brain is like a computer – it has networks and pathways that receive these signals and share them with other areas in the brain, to make sense of and use them to see. 

In CVI, the eyes are working correctly, but the brain has trouble using, sharing or interpreting the signals sent through. 

Different parts of the brain have different functions in this process. For example, one-part (the visual cortex, which is in the occipital lobe) processes what you see, while other parts help you understand where objects are (the parietal lobe) or recognise what they are, like faces (the temporal lobe).

Depending on where in the brain the damage is, different aspects of vision can be affected. That’s why CVI can present very differently from one person to another.

CVI was originally called cortical visual impairment because the problems were thought to be in the visual cortex. It’s now more often called cerebral visual impairment, because the damage can be to the visual pathways or to one of the different processing centres in the brain. 

What causes cerebral visual impairment?

CVI is caused by damage or abnormal development in the parts of the brain responsible for vision. This can happen for many reasons, often because of an injury to a baby’s brain before or during birth. It often happens alongside other conditions caused by a problem with the brain, such as cerebral palsy or developmental delay.

It can be caused by:

• Brain surgery: Surgery to treat conditions like tumours or epilepsy can sometimes damage parts of the visual pathway.
• Head injury: A brain injury can damage the visual pathways.
• Hydrocephalus: This is a build-up of fluid in the brain that can increase pressure and cause damage.
• Infections: Infections that reach the brain, such as meningitis or encephalitis, can damage brain tissue.
• Lack of oxygen or blood supply: This is a common cause of CVI. It can happen due to a stroke in the womb or during birth or can be linked to prematurity.
• Metabolic diseases: These are disorders (often genetic) that affect how the body converts food into energy and can sometimes lead to brain damage.
• Periventricular leukomalacia[CW6.1]: This is an injury to the white matter of the brain, most often seen in babies born very prematurely.

These causes are listed alphabetically, not necessarily in order of frequency. 

Why is cerebral visual impairment more common in babies and children?

CVI most often develops in babies and children because their brains are in a critical period of development. An injury to the brain early in life, when it is still forming connections, can significantly impact how visual pathways develop.

Medical advances have led to much better survival rates for babies who are born premature or who experience neurological damage around the time of birth. This progress means that more children are surviving with conditions that can lead to CVI. 

CVI often lasts for life, so adults can be affected by CVI as well. In some cases, CVI is present from birth but is not diagnosed until adulthood.

Sometimes, CVI can develop for the first time in adults or older children. This is called acquired CVI. It can be caused by many of the same things that can cause CVI in babies, such as a head injury or infection. It can also be caused by dementia, such as Alzheimer's disease.

What are the symptoms of cerebral vision impairment?

The signs and symptoms of CVI can vary a lot from person to person. Because the issue is with how the brain processes vision, a child with CVI might have healthy eyes but behave as if they cannot see well. Vision can seem to change from one day to the next, or be affected by how tired, unwell, or overwhelmed a person is feeling.

Common symptoms of cerebral visual impairment include:

• Being sensitive to light, or staring into light (like lamps or the sun)
• Not looking into people’s eyes or fixing on objects for long
• Difficulty following moving objects with the eyes
• Uncontrolled eye movements (nystagmus)
• Only seeing some parts of what’s in front of them (visual field loss)
• Issues with spatial awareness such as bumping into things, difficulty understanding distance between objects and challenges locating objects
• Getting tired when doing tasks that need vision
• Seeing moving objects better than still ones
• Seeing colour better than black and white
• Trouble recognising familiar people, places or objects
• Trouble picking out one item in cluttered environment

Children with CVI may also have other conditions such as cerebral palsy, epilepsy, learning difficulties or hearing loss.

How is cerebral visual impairment diagnosed?

Currently, there is no standard pathway for CVI diagnosis and the route to a diagnosis can vary from place to place. As CVI usually affects children with developmental or medical conditions, a good place to start is discussing concerns with your GP or paediatrician (a doctor who is specialised at managing medical conditions affecting infants, children and young people) and asking for a referral to an ophthalmology clinic.  

Key to a diagnosis is an eye and vision check and brain-related vision function tests. The specialist may ask questions about the kinds of issues you have noticed, and which types of situations (like recognising faces, or when there are a lot of things to look at) seem most challenging. 

The specialist might refer your child for other tests, such as electrophysiology, which can measure the electrical signals being sent from the eye to the brain, or MRI (Magnetic Resonance Imaging) scans, which can show the parts of the brain that are involved in vision. However, these tests are only occasionally useful. 

Sometimes tests for developmental delay or other neurological conditions will be done, too. There are lots of different tests that can be done to assess different aspects of vision. For young children, some of these might be presented as games for them to play.  

What are the treatments for cerebral visual impairment?

While there is currently no cure for the damage to the brain that causes CVI, there are things that can help people make the most of their vision and learn to navigate the world. Treatment is about support, understanding, and creating the best possible environment for learning and development.

Early intervention can make a difference, especially for babies and children whose brains are still developing. Support often involves a team of specialists working together with the family. 

Evidence is building about what kind of treatments work best, but we are still at the beginning of finding the best way to help. The most effective strategy will depend on the person who is affected, how they’re affected and what they find helpful. Some common techniques include:

• Adapting the environment: For babies and children, this might mean using toys with specific colours they respond to, reducing clutter in their room, or ensuring lighting is comfortable. At school, it could involve ensuring good contrast and giving the child a front-row seat away from distractions. Read more about a study we’re funding on understanding the challenges of clutter for people with CVI. 
• Techniques to help with reading: This might include large print, extra line spacing or word spacing, using a magnifying glass, covering up other text, or trying a tilted or a raised book stand or workstation.
• Building visual skills: Therapists and specialist teachers can work with children to help their brains learn to interpret visual information more effectively. This might involve structured activities and play designed to build visual attention and recognition.
• Using other senses: Encouraging the use of touch and hearing can help a person with CVI to learn about their environment. For some people, techniques for dealing with vision loss, such as Braille, learning independent living skills, and orientation and mobility skills, can be helpful. For adults who acquire CVI, vision rehabilitation can help them adapt to their vision loss and learn new strategies for daily tasks.
• Correcting any eye problems: If a person with CVI also has a condition like short-sightedness, wearing glasses or contact lenses is very important. This ensures that the visual signal sent from the eyes to the brain is as clear as possible. If they have nystagmus, allow them to hold their head at the angle where the eye movements are least and vision is best. 

Can cerebral visual impairment improve over time?

Research shows that the vision of children with CVI often improves over time, although not to the quality of vision possible in the absence of CVI. We don’t know for sure why this improvement happens. It may be that the brain’s ability to change and adapt, known as neuroplasticity, means that new connections can be formed.

Improvement is not guaranteed and it’s hard to predict exactly what an individual’s journey will look like. Early diagnosis and starting support services as soon as possible gives the best chance for a child to reach their full potential[CW15.1] by using “work arounds” to adapt settings and tasks as much as possible to visual needs and to avoid the anxiety that can develop if a child’s difficulties are unexplained. 

The goal is to help people with CVI learn to access their world in a way that works for them, using a combination of their vision and other senses.

Latest research on cerebral visual impairment

Research into cerebral visual impairment is looking for better ways to diagnose the condition early and more effective strategies for rehabilitation and support. While it is not yet possible to repair the damage in the brain’s visual pathways, research could help prevent or reduce some of the causes, like lack of oxygen at birth.

Improving brain imaging techniques and developing more accurate vision tests will help doctors and therapists to diagnose CVI sooner and understand the specific challenges each child faces. This allows for tailored support to be put in place more quickly, helping children to develop and learn as fully as possible.

Dr Kathleen Vancleef: Understanding the challenges of clutter

Fight for Sight is supporting the work of Dr Kathleen Vancleef at Durham University, whose research is focused on a problem that affects around 80 percent of children with CVI: dealing with clutter.

Busy environments like classrooms, playgrounds, or even a messy bedroom can be visually overwhelming for a child with CVI. Their brains cannot process the huge amount of visual information as quickly as others can, which can cause distress and make it hard to concentrate on learning or playing.

Dr Vancleef’s project aims to understand exactly why clutter is such a challenge. The research is exploring two main possibilities:

1. Children with CVI may struggle to combine different visual elements, like colours and shapes, that belong to a single object (a difficulty known as apperceptive agnosia).
2. They may only be able to see one object at a time (known as simultanagnosia). Imagine trying to pour a drink but only being able to see either the glass or the water, never both together.

By understanding the root cause of these difficulties, the project hopes to provide better, more personalised advice to parents, teachers and carers. The ultimate goal is to develop free online tools, including questionnaires and simple tasks, that can help identify a child’s specific visual challenges. This will empower families and professionals with the knowledge to create better environments for children with CVI, for example, by removing unnecessary items from a desk during schoolwork, helping them to thrive.