Thoughts on Charles Bonnet Syndrome

Possibly the most important lesson that should be taken from the story of Charles Bonnet Syndrome (CBS) is that correlation implies nothing about causation and even less about etiology.

Patients with general dementia, Alzheimer’s, or strokes were far more likely to communicate seeing things that weren’t there. So if you merely look at reported population statistics, visual hallucinations would seem to be associated very strongly with brain damage.

But the real problem was that such patients were much more likely to be uninhibited in talking about their hallucinations. Older people with loss of sight but properly-working minds feared the consequences of mentioning what they saw to anyone – at least partially because of the existing association in physicians’ minds between visual hallucinations and senility – and so said nothing. And so there was no awareness of the true rate of the phenomenon.

If you look at the actual statistics – the ones collected once the stigma of CBS was reduced, physician awareness increased, and elders gently but insistently questioned – then there’s no particular association between senility or brain disease and the hallucinations.

Remember – it took hundreds of years for the condition to even be mentioned in the English language, despite all of the people who must have experienced vision loss and CBS in that time. Despite all of the physicians who must have aged or had eye damage and suddenly experienced it themselves.

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