‘Where can I get a diagnosis for cerebral vision impairment?’
‘I have cerebral vision impairment: Can I get registered for sight impairment or severe sight impairment?’
These are common questions from patients with visual perceptual difficulties, also known as cerebral vision impairment (CVI). The question is simple: The answer is not!
Adults with acquired brain injury
Adults with acquired brain injury, such as stroke, tumour, or brain damage from a high impact acccident often present with acute symptoms. Certification of sight impairment is fairly straightforward if the brain injury leads to basic visual processing dysfunction, such as reduced visual acuity or a visual field defect (see Blog 1 in this series for eligibility criteria). It can be more challenging if the brain injury is slowly evolving over time, such as with degenerative brain conditions, or if the visual dysfunctions are caused by brain damage or malfunction of brain areas where higher visual processing takes place. The current guidelines for certification (‘Explanatory Notes for Ophthalmologists') provide guidance on basic visual processing parameters (visual acuity and visual fields), but not on higher visual processing parameters. However, CVI can lead to significant difficulties in a person’s everyday life. Common features are for example, prosopagnosia (not recognising faces), topographic agnosia (getting lost in familiar environments), optic ataxia (not reaching accurately/ finding it hard to judge where things are in three dimensional space), and coping in busy environments due to dorsal stream dysfunction. These patients may not be able to stay independent due to these difficulties in visual memory and visuo-spatial orientation.
The Explanatory notes do mention that certification is ultimately a matter of professional judgement by the ophthalmologist, who decides if a person’s vision significantly impacts their everyday function. The certification form includes cerebral vision impairment as a possible cause. Therefore, it is possible to certify a patient with cerebral vision impairment.
I carried out a survey among ophthalmologists a few years ago, and it became clear that ophthalmologists are a lot more confident about certifying patients with ocular vision impairment, compared to cerebral vision impairment.
Adults with congenital cerebral vision impairment (CVI)
I come across more and more patients with childhood CVI, who were previously unaware of their condition. Many of these adults have experienced difficulties as a child growing up, as their vision impairment was not identified, and therefore no supportive strategies were offered. Instead, they were being regarded as being ‘clumsy’, ‘uncooperative’, ‘retarded’ or ‘badly behaved’, or they were given labels such as dyslexia, ADHD or ASD. When I see them as adults and discover their cerebral vision impairment, this is often experienced as a relief. The explanation of their condition, along with recommendations for adaptive strategies opens doors for them that had been closed up to that point. It can truly be a life-changing experience when they finally understand the underlying cause for their visual difficulties and different behavioural features. The question then arises: Should this patient be certified for their vision impairment? I would argue that it depends on the severity and nature of their visual difficulties. If their visual difficulties have a significant impact on their everyday life, they are eligible for certification. It is less straightforward to quantify visual difficulties from higher visual processing dysfunction (compared to basic visual functions), and therefore clinical judgement from a professional who has a solid understanding of CVI is required to decide whether a patient should be offered certification of sight impairment. In my experience, a good relationship with a neuro-ophthalmologist is key as they have the requisite knowledge, skills and understanding to certify patients with CVI.
Children with cerebral vision impairment (CVI)
In Scotland, children are not registered until they reach 16 years of age. Up to that point, they are considered for support if they meet the criteria set out by the Vision Impairment Network for Children and Young People (VINCYP).
https://www.nn.nhs.scot/vincyp//professional-resources/
In England and Wales, children can be certified in the same way as adults.
Conclusion
There is currently no international consensus regarding diagnosis of cerebral vision impairment, and therefore the approach differs between health boards. Cerebral vision impairment is a field which requires more research to reach a consensus about the diagnosis, and about eligibility for certification.
