Whilst Katherine does not see through her left eye, this has little effect on her visual field.

To demonstrate, try this:

• look straight ahead and focus on something straight ahead
• next hold your left arm out at a right angle (as we did when discussing visual fields in the previous chapter).
• wiggle your fingers, and slowly, whilst looking at the object in the centre of your vision
• move your arm towards the centre until you are aware of your wriggling fingers in your periphery vision.
• now close your left eye and consider how the image in front of you has changed.
• the object you were looking at is still in the middle - because both eyes were looking at the same thing - it is still central to the right eye.
• by closing your left eye, you have not lost the left half of your vision
• you have only lost part of your vision on the far side to your left because your nose gets in the way (turn your head the left while still looking straight ahead and you will see more on the left side).

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:

• low visual acuity in her good eye
• poor contrast sensitivity in her good eye
• she is moving too fast

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.

Also in this section...

• Katherine’s Playground Pre-CVI
• Katherine’s Playground Level 1
• Katherine’s Playground Level 2
• Katherine’s Playground Level 3
• Katherine’s Playground Further Suggestions
• Katherine’s Playground The Technical Stuff
• Katherine’s Playground Follow Up (to follow)

• Contents