Treating Visual hallucinations in people with Macular Degeneration: a non-invasive stimulation study

Funders: Macular Society, Fight for Sight, Thomas Pocklington Trust

Collaborators: Dr John-Paul Taylor, Dr Dominic ffytche, Katrina da Silva Morgan, Dr Greg Elder, Dr Daniel Collerton

Aims/Objectives: 1) To investigate whether visual hallucinations in Charles Bonnet Syndrome are the consequence of over-activity in visual parts of the brain. 2) To examine whether repeated transcranial direct current stimulation (tDCS) can be used to decrease over-activity in the brain and subsequently treat visual hallucinations in Charles Bonnet Syndrome.

Charles Bonnet Syndrome (CBS) occurs in patients who experience recurrent visual hallucinations in the presence of a visual impairment, such as macular degeneration, and in the absence of psychiatric illness. It is estimated that up to one-third of people experiencing CBS find the hallucinations to be distressing or disruptive to everyday life. Currently, there are no effective treatments for CBS meaning that there is a distinct need to develop new and effective therapeutic interventions. 

Previous research has suggested that visual hallucinations in eye disease are the result of increased activity in the visual parts of the brain. As the brain is deprived of sensory information from the eyes, due to visual impairment, this causes spontaneous activity to occur in the visual system resulting in hallucinations. Transcranial direct current stimulation (tDCS) is a non-invasive (i.e. applied from outside of the brain) technique which can be used to alter the activity of parts of the brain using a weak electrical current applied through electrodes on the scalp.  

In this study we are recruiting people with eye disease who experience frequently reoccurring visual hallucinations to a double blind placebo controlled crossover trial of tDCS. The crossover means that participants will each receive a course of active tDCS or placebo tDCS over several days, returning after a four week period to receive the opposite treatment. In addition, all participants will undergo assessments of their visual function, visual hallucination severity, and measures of their cortical excitability (brain over-activity) using brain imaging techniques, electroencephalography (EEG) and non-invasive transcranial magnetic stimulation (TMS). We are also recruiting people with eye disease who have never experienced visual hallucinations to complete the same measures of cortical excitability in order to observe differences between people with and without Charles Bonnet Syndrome.

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