More on the enigma of blindness and psychosis

A long-standing enigma in psychiatry has been why no-one has been able to find someone who has both congenital blindness and a diagnosis of schizophrenia. The newest and most comprehensive archive study to date has just been published on exactly this issue although it raises more questions than it answers.

Evelina Leivada and Cedric Boeckx from the University of Barcelona in Spain conducted an extensive medical literature search and did come up with some cases of congenital blindness and schizophrenia – 13 in total, although only two case studies (outlining a total of four cases) were found which were convincing enough to be unaffected by other serious problems, like severe genetic disorders.

And these remaining four were hardly straightforward and as one report was from 1943 and the other from 1967 where standards of both vision and psychiatric assessment were significantly short of modern standards.

Notably, all cases of co-occurrence were from blindness due to eye problems or where blindness happened relatively late (after 6 years of age). No cases were found were people had a diagnosis of schizophrenia and were congenitally cortically blind – where blindness was caused by problems with the brain’s visual system.

What this new study provides is weak evidence for the possibility of certain sorts of blindness coexisting with a diagnosis of schizophrenia and more comprehensive support for the curious finding that blindness seems to reduce the risk of developing psychosis.

It’s worth noting that what is really needed is a prospective epidemiological study of psychosis in blind people. However, researchers have been searching for congenitally blind people with psychosis since the issue of non-co-occurrence was first seriously raised in the 1980s and none have been found. Based on the rates of occurrence for each condition, the combination should be fairly common. This suggests that hypothesis of protective effects of congenital blindness needs to taken seriously.

The Leivada and Boeckx paper goes on to speculate about neuropsychological reasons why congenital blindness might protect against schizophrenia (essentially, changes in the interaction between key visual system components and the language system) and, somewhat less convincingly, genetic reasons – as just extrapolating likely genes from case studies is very speculative and both the eye and brain develop from the same cells during embryo development so it’s not clear shared genes won’t just reflect generally impaired neurodevelopment.

I have to say, I find the concept of schizophrenia to be a fairly useless, but if the increasingly plausible hypothesis that congenital blindness protects against psychosis is confirmed, it has interesting implications for those that argue that psychosis is nothing but the result of marginalisation, stigma or difficult life circumstances where biological explanations are irrelevant.

Blindness, clearly would increase your chances of all of these, and so on this theory, we would expect an increased rate of psychosis, but this doesn’t seem to be the case.

It’s not that marginalisation, stigma or difficult life circumstances aren’t causal factors in developing psychosis, they clearly are, but ignoring neuro-level explanations outside these effects is equally as narrow as suggesting that they are the only relevant influences.

 

Link to ‘Schizophrenia and cortical blindness’ in Frontiers.