There’s a striking resemblance between some of the hallucinations described to me recently by a senior ICU nurse, and Oliver Sacks’ description (in his book ‘Hallucinations’) of Charles Bonnet syndrome – hallucinations in those losing eyesight. Almost all of the people I have spoken to have talked about the limited light levels they perceive in their hallucinations, and one at least has mentioned specifically that her eyesight – normally excellent – was compromised in ICU. I wonder whether – along with sensory deprivation, drugs, trauma, and every other likely cause in ICU, diminished visual perception plays a part in people’s propensity to hallucinate?
‘They’re often really intense, so very vivid, and often very colourful, so they will attribute really – and we’re not talking insipid colours, they’re always really vibrant colours – so the colours that spring to mind are like the fluorescent turquoise, greens, oranges, those sort of colours. And they will often have persecutory hallucinations. And also they may well have Capgras hallucinations as well, where they may see aliens, or they see human bodies with a horse head or something like that.’