It’s a phenomenon that’s stumped even the smartest scientific brains for decades: No one born blind has ever been diagnosed with schizophrenia. And though there have been countless studies conducted to test the theory, none have been as comprehensive as one published in Schizophrenia Research in 2018, which looked at whole-population data from 467,945 children born in Western Australia between 1980 and 2001. Over the course of the study, scientists found that of the 1,870 children (0.4 percent) who developed schizophrenia, none were born blind.

The anomaly has led researchers to believe there’s something about congenital blindness that, in fact, protects people from developing the condition. But what? There are two ideas: cognition and vision.

The Cognitive Factor

While there is no definitive answer yet, researchers have many hypotheses, says Thomas Sedlak, M.D., director, Schizophrenia and Psychosis Consult Clinic and assistant professor of psychiatry and behavioral sciences at Johns Hopkins Medicine. “One theory might be that a person blind from birth learns to think in ways that are protective, or the brain learns to use that extra cortex in ways that are protective,” Dr. Sedlak says. So, what does that mean, exactly?

While the most characteristic symptoms of schizophrenia are the psychotic ones such as hallucinations and delusions, scientists believe that these are not actually the core features of the disease. Instead, research suggests that the main features are cognitive dysfunctions—in things like memory, perception, learning, language, and attention, and that these impairments are even more common than psychotic symptoms.

In contrast, “people who are born blind have more developed aspects of other senses,” says psychiatrist Frank Chen, M.D., chief medical officer, Houston Behavioral Healthcare Hospital. These include things like auditory processing, attention, scent, and memory—which are deficient in those with schizophrenia.

Because they have a lack of vision, people born blind learn to overcompensate at an early age by heightening these other senses, Dr. Chen says. The belief is that these kinds of enhanced skills have a protective effect from developing the exact opposite impairments, which come with schizophrenia.

For example, those with schizophrenia have a hard time processing the sounds of speech and where it’s coming from. This kind of deficit in sound localization can make it difficult for them to even realize that the sound of their voice is in fact coming from themselves, which can contribute to delusions.

The Internal & External View Of The World

People with schizophrenia have been shown to have problems with their vision, including retina issues, unusual eye movements, and abnormal blinking rates. These visual abnormalities have even been noted to occur before psychotic symptoms manifest, which can sometimes be predictive of a schizophrenia diagnosis.

Scientists believe that when someone’s vision is abnormal, the brain receives all kinds of confusing signals about the world, so they have to make more predictions in order to make sense of it all. Since vision is affected, they can’t pick up on inconsistencies between what they know to be true from past experiences and what’s happening in real-time sensory information—so they end up making false predictions.

This is what scientists think causes hallucinations and delusions. Even healthy people, however, can experience hallucinations when their vision is temporarily blocked for just a few days, researchers say.

On the other hand, scientists hypothesize that when someone is blind from birth, the brain is conditioned to make sense of all of that sensory information coming in by relying on other cues to build a mental picture. So, in theory, they wouldn’t make false predictions about the world around them and would be less susceptible to psychotic symptoms. In effect, they are protected from the false visual cues associated with schizophrenia.

What It All Means

Though a hard and fast explanation for the absence of schizophrenia in congenital blindness remains to be unfurled, these hypotheses are grounds for hope in understanding and treating the condition. These findings can help in three ways:

  • Determining risk. Eye tests, rather than blood tests, could be used as a predictive measure to determine a high-risk factor for schizophrenia.
  • Informing early intervention. Researchers believe this data shows that early visual and cognitive training that focuses on improving sensory perception as well as things like memory and attention could potentially help people at high risk for the disorder.
  • Dealing with symptoms. Sharpening and relying on senses other than vision may help enhance functioning in people with schizophrenia.
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Last Updated: Aug 14, 2020