Following on having been inappropriately surprised that a person with dissociative identity disorder (DID) might be allergic to orange juice whilst under control of some personalities but not others, I’ve now learned that it’s possible for some personalities to be blind when others are not.

Here we have a report of a patient known as B.T. She seemed to have been blinded as the result of an accident, and got the appropriate medical tests and later diagnosis for cortical blindness as a result of damage to her brain.

She also had DID. Imagine everyone’s surprise a few years later, being of the chronological age of 37 years old, when at the times when the personality of a teenage boy was in control she could see well enough to read.

It’s not that B.T. had just reported not being able to see for years. Brain tests showed that when in other personalities the areas of her brain associated with visual stimuli didn’t react to input at all, as one would only expect in anyone unable to see . But when in the personality that was able to see, the sight processing areas of the brain started to light up again.

Over time, with training, most of her other personalities learned to see again, although two remain blinded.