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Gordon Dutton’s Blog (12) Not knowing what one does not know

Not knowing what one does not know: a fundamental issue in cerebral visual impairment (CVI).

I've been privileged to give many talks about cerebral visual impairment to a wide range of audiences. On a number of occasions, a member of the audience has approached me afterwards to say they have just realised that they must have a form of CVI themselves. They'd had their difficulties for years but had not realised why, until they heard their symptoms described in the lecture.

Why is this?

The answer is that they did not know that they did not know about their visual condition, so could not tell anyone about it. They had never known that such an explanation for their difficulties existed.

  • Gnosis is Greek for knowledge
  • Agnosia means not to know.

If one does not know that one does not know, this is called an anosognosia. This is an important concept in the field of CVI.

So how can CVI be an anosognostic condition?

There are a number of good reasons.

  • 1. Our brains visually map our surroundings without us knowing. For example, we're not really aware of the location of each and every step as we run up a flight of stairs. Our movements take place automatically, without our being consciously aware of how they were planned. No more are we conscious of all the people in a crowd, as we make our way quickly through a busy thoroughfare. This too takes place automatically. So if these abilities become impaired, or have always been diminished owing to injury to the back of the parietal lobes of the brain, there is a puzzling lack of awareness for the resulting difficulties, despite their being observed by others. In other words, it is difficult to know that one has lost what was previously a non-conscious ability.
  • 2. Children who are born with a visual disability or who acquire such a disability during very early childhood of course know that their vision is normal to them.
  • 3. As it is our brains that create the conscious image of what we see, brain injury can lead not only to lack of vision, but also to lack of awareness of the loss.

A symptom is defined as...


a physical or mental feature which is regarded as indicating a condition of disease, particularly such a feature that is apparent to the patient.

The final phrase '...that is apparent to the patient', is key.

In other words, despite CVI being disabling, those affected often do not know that they have the problem, because the condition is anosognostic and therefore is not symptomatic. This means they can't go to the doctor to say what the matter is, because they can't know.

Here the plot thickens!

As CVI is often asymptomatic, doctors rarely see affected individuals.

So not only are people with CVI commonly anosognostic for their condition, but so is society as a whole.

That's why websites like CVI Scotland, that aim to inform everyone about CVI are important. Once people with CVI, or those who look after them, have learned that their difficulties are due to CVI, they cannot unlearn it, so they no longer have anosognosia, and this can be the first step on the pathway to habilitation or rehabilitation.


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