How do I manage functional visual loss

Abstract

Functional visual loss is a subtype of functional neurological disorder (FND) and is a common cause of visual impairment seen in both general and neuro-ophthalmological practice. Ophthalmologists can generally diagnose functional visual loss reasonably confidently but often find it harder to know what to say to the patient, how to approach, or even whether to attempt, treatment. There is little evidence-based treatment despite studies showing up to 60% of adults having impactful symptoms on long-term follow-up. The last 20 years has seen large changes in how we understand, approach, and manage FND more widely. In this article, we set out our practical approach to managing functional visual loss which includes : 1) Make a positive diagnosis based on investigations that demonstrate normal vision in the presence of subjectively impaired vision, not just because tests or ocular exam is normal; 2) Explain and label the condition with an emphasis on these positive diagnostic features, not reassurance; 3) Consider eye or brain comorbidities such as migraine, idiopathic intracranial hypertension or amblyopia; 4) Consider working with an orthoptist using diagnostic tests in a positive way to highlight the possibility of better vision; 5) Develop simple treatment strategies for photophobia; 6) Consider psychological factors and comorbidity as part of assessment and therapy, but keep a broader view of aetiology and don't use this to make a diagnosis; 7) Other treatment modalities including hypnotherapy, transcranial magnetic stimulation and more advanced forms of visual feedback are promising candidates for functional visual loss treatment in the future.

Fig. 1

A predisposing, precipitating and perpetuating model of aetiology can combine with a mechanistic understanding of functional visual loss at the level of the brain.

Fig. 2. In functional visual loss a tubular visual field arises primarily because of a strong “prediction” of tunnel vision in keeping with an / predictive processing model of how the brain works.

It can be explained to the patient as evidence that the brain is ‘suppressing’ vision to match an internal model. Reprinted from Stone et al. [18].

Fig. 3

A model of functional visual loss highlighting the mismatch between “top-down predications” and “bottom-up” visual input and how potential therapies can target this.

Fig. 4. The ‘Peekaboo’ app is an example of how technology for visual testing could be used to help treatment of visual loss.

Observing saccades towards the striated target enables examiner and carer to infer the patient has seen it, even if the patient reports they do not see it. In addition, the patient can be asked to guess where the target is by touching the screen even when they can’t see it. This can help gauge/ prove to the patient whether their ‘brain’ can still see, even if they don’t have visual experience.