Whilst Katherine does not see through her left eye, this has little effect on her visual field.
To demonstrate, try this:
The curve out of the bottom left corner is where the tip of her nose blocks her vision - she can see the tip of her nose, it is not missing. Katherine has a slightly narrower left peripheral visual field as well because of the bridge of her nose.
Because the brain can create a full visual field from one eye, people with vision from only one eye are still permitted to drive.
What Katherine doesn't have however, is binocular vision, that is a single image created from combining the visual information processed from the two eyes. Whilst Katherine's picture is good, the lack of binocular vision affects her sense of seeing in depth, because the visual information only comes from one eye. This may mean that in unfamiliar places, Katherine may miss occasional obstacles on her left, and extra care needs to be taken.
Other reasons why Katherine has trouble recognising her mother may be because she has:
Katherine's mother has confirmed that Katherine's clarity of vision and contrast sensitivity are both good in her right eye, however she was running and this may have been a factor. For some people movement, if too fast, makes seeing clearly very challenging. This is called dyskinetopsia.
However, Katherine, when she stopped running and approached the wrong person didn't immediately realise her mistake, which suggests moving too fast was not the cause.
With this knowledge, technically, there is no reason why, with the vision from her right eye alone, she would have problems recognising faces.
So we take what we know and carry it along the pathway to Level 2.
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