Since the middle of the last century, researchers have been looking at a curious link - it seems that being born blind protects people from developing schizophrenia. Now, a large scale study has just added more evidence to confirm this is indeed the case.
In particular, cortical blindness – caused by abnormalities in the brain, rather than damage in the eyes – seems to be incompatible with having schizophrenia.
According to the authors of this latest research, no incidents of schizophrenia in cortically blind people have ever been recorded to date.
The researchers analysed data from 467,945 children born in Western Australia between 1980 and 2001. In this sample, 1,870 children (0.4 percent) developed schizophrenia, but none of the 66 children in the sample who were born with cortical blindness ended up getting a schizophrenia diagnosis.
"The protective phenomenon observed in case studies of people with congenital cortical blindness, and now supported by our whole-population data, warrants careful, clinical investigation," write the researchers from the University of Western Australia.
What makes the findings especially notable, besides the large sample size, is their potential for telling us more about how schizophrenia works – and how it might be better treated in the future.
It's important to note a few limitations, not least the long-standing adage that absence of evidence is not evidence of absence. What we mean is that these numbers alone don't prove that cortical blindness is the key factor in eliminating schizophrenia.
The authors also note their data only covers people aged 14 to 35; some schizophrenia cases may get reported later on in life.
However, considering how the research fits with previous case studies, this relationship looks well worth exploring in the future.
But if cortical blindness does indeed have a "protective phenomenon" against schizophrenia, what's going on?
More work will need to be done before we can be sure, but one hypothesis is that being born blind leads to natural enhancements in areas of the brain that are usually malfunctioning in cases of schizophrenia – areas covering sound perception and attention, memory, and the use of language.
The study found that schizophrenia rates were lower than normal in people with peripheral blindness too – 0.2 percent of the sample – but peripheral blindness doesn't involve changes in the brain as much as cortical blindness does.
In fact the link could extend to other psychotic illnesses, some experts have suggested. It's possible that disconnects with reality that affect the sensory systems in the brain aren't quite as likely when people have been blind since birth.
And that might open up new possibilities not just for treatment, but also for catching signs of the condition ahead of time, and trying to minimising its effects at the earliest possible stage.
The study "offers hope of identifying potential targets for early intervention and prevention in schizophrenia" write the researchers, "including therapeutic strategies directed at the reorganisation of cortical functioning and early cognitive training with an emphasis on sensory-perceptual functioning."
The findings have been published in Schizophrenia Research.