Transcranial Direct Current Stimulation in the Treatment of Visual Hallucinations in Charles Bonnet Syndrome: A Randomized Placebo-Controlled Crossover Trial

Abstract

Objective: To investigate the potential therapeutic benefits and tolerability of inhibitory transcranial direct current stimulation (tDCS) on the remediation of visual hallucinations in Charles Bonnet syndrome (CBS).

Design: Randomized, double-masked, placebo-controlled crossover trial.

Participants: Sixteen individuals diagnosed with CBS secondary to visual impairment caused by eye disease experiencing recurrent visual hallucinations.

Intervention: All participants received 4 consecutive days of active and placebo cathodal stimulation (current density: 0.29 mA/cm²) to the visual cortex (Oz) over 2 defined treatment weeks, separated by a 4-week washout period.

Main outcome measures: Ratings of visual hallucination frequency and duration following active and placebo stimulation, accounting for treatment order, using a 2 × 2 repeated-measures model. Secondary outcomes included impact ratings of visual hallucinations and electrophysiological measures.

Results: When compared with placebo treatment, active inhibitory stimulation of visual cortex resulted in a significant reduction in the frequency of visual hallucinations measured by the North East Visual Hallucinations Interview, with a moderate-to-large effect size. Impact measures of visual hallucinations improved in both placebo and active conditions, suggesting support and education for CBS may have therapeutic benefits. Participants who demonstrated greater occipital excitability on electroencephalography assessment at the start of treatment were more likely to report a positive treatment response. Stimulation was found to be tolerable in all participants, with no significant adverse effects reported, including no deterioration in preexisting visual impairment.

Conclusions: Findings indicate that inhibitory tDCS of visual cortex may reduce the frequency of visual hallucinations in people with CBS, particularly individuals who demonstrate greater occipital excitability prior to stimulation. tDCS may offer a feasible intervention option for CBS with no significant side effects, warranting larger-scale clinical trials to further characterize its efficacy.

Keywords: Charles Bonnet syndrome; Macular degeneration; Noninvasive stimulation; Visual hallucinations.