Terry Pratchett, the fantasy writer, wrote a clear-headed and deeply personal article about having been diagnosed with Alzheimer’s. The type of dementia he has is called posterior cortical atrophy (PCA), apparently the “best” form of Alzheimer’s to have: memory and coherency are largely left unaffected (at least at the beginning), but visual acuity and skilled movements show a decline because the brain cells damage is focused on the region that controls visual processing.

On reading about PCA, I was struck by the similarities between it and the cortical visual impairment that Jon has, and the symptoms on one of the fact sheets put out by the UK Alzheimer’s Society could be a point-by-point description of Jon’s visual issues:

However, in people with PCA, visual problems are not due to problems with their eyes. Rather, the affected brain cannot interpret and process the information received from the person’s eyes, which are still healthy.

The visual problems experienced may vary widely but often include some or all of the following:

• Difficulty recognising objects in pictures (for example household items in a catalogue, especially if the pictures were taken from obscure angles or the picture is incomplete).
• Difficulty recognising faces (for example TV characters, friends, relatives).
• Decline in spatial awareness, for example in judging distances and speeds. This might result in the person missing when reaching out to pick something up, finding it hard to press the correct numbers on a telephone, experiencing difficulties with driving or descending stairs, and in judging the speed of moving traffic. Stationary objects may also appear to move.
• Difficulty moving from the end of one line to the beginning of the next when reading.
• When reading, particular words or letters appear to move around or become superimposed over one another.
• Difficulty in reading certain types of text (for example large print such as newspaper headlines, handwritten notes).
• Experiencing increased sensitivity to bright light or shiny surfaces.
• Experiencing double vision or feeling that their eyes are jerking around or not completely under their control.
• Particular difficulty seeing clearly in fading or low light conditions.

Some problems may be particularly hard to understand – for instance small print may be easier to read than large print – or objects that are ‘just under someone’s nose’ are not recognised and then suddenly ‘seen’. These problems, especially if not clearly explained, may be a particular cause of frustration for those around the individual with PCA as well as for the individual themselves.

We can certainly vouch for the “hard to understand” bit. Two of Jon’s early teachers simply refused to understand Jon’s issues, ignoring strong suggestions by Jon’s vision consultant. One teacher dismissed concerns about laminating reading materials (because of the glare off the fluorescent lighting), and intentionally did so. Often people think that Jon’s turning his head away from the person speaking is a behavioural issue (“he’s not paying attention”) whereas it is actually proof that Jon is desperately trying to see the person – using any means he can – to overcome his nystagmus (involuntary eye movements). He often has to resort to using his peripheral vision in sidelong glances, which unsettles people. Jon’s eye specialist has warned us that we’ll have to stress this to all his new teachers, and we’ve tried to do this, with varying success.

Many people assume Jon’s visual difficulties are due to focusing issues in the eye (especially since Mom and Dad both wear glasses for nearsightedness), but his eyeballs are just fine. (As regular readers know he did need glasses for a time, but currently does not. Very strange.) It’s hard enough for us to understand the unpredictability of Jon’s cortical deficits, so no doubt it’s far harder for other, less closely-connected, people.

Jon’s behaviour – lack of close friends, inability to pretend, etc, has even been likened to autism by some (including one of his finest teachers). He does exhibit some autistic characteristics at times, but he would never be classified as autistic. But much of Jon’s odd behaviour is actually his coping with complex aspects of his damaged vision. Sometimes we wonder if he has much of an ability to distinguish faces, (a little like the stroke victim in Oliver Sacks’s The Man Who Mistook His Wife for a Hat). When Jon sees an animated TV character in a situation where a different voice actor has been hired, he pounces on it immediately. Is that his primary way of identifying people?

So articles like Pratchett’s give us a little more insight into the intricate perceptual processes that are taking place in our brains, and maybe get us a little closer to understanding how Jon is trying to decode his world.