For this lesson it is assumed you have read Lesson 3d Visual Fields, Lesson 6a Hemianopia and Lesson 6d Lower Visual Field Impairment. We pick up on concepts explained in these lessons so please read or review them if needed.
Think about your visual field and what you are looking at right now. In your mind divide the picture into quarters, top and bottom, left and right.
In relation to the visual field, each of the four quarters is called a quadrant. Quadrant is from the Latin for quarter, meaning one part of four.
Superior and inferior do not mean one is more important than the other, they are just old anatomy terms that are still used, meaning upper and lower.
Let's think about how each of these quarters come about, picking up on the visual process of visual information travelling through the brain, along bundles of fibres called the optic radiations (lesson 3d).
The upper part of the optic radiations serves the lower (inferior) visual field and splays out through the posterior parietal lobes. If there is damage to this part of the brain, it can affect the optic radiation causing reduction in vision or complete vision loss in the lower visual field, typically on both sides (lesson 3d and lesson 6d).
The lower part of the optic radiation serves the upper (superior) visual field, and takes an S-shaped pathway through the temporal lobes on both sides. If there is damage to either temporal lobe, it can affect the optic radiation causing reduction in vision or vision loss in one of the upper (superior) quadrants, opposite to the side of the damage.
The destination of the optic radiation is the occipital lobes where the picture you can see is created.
The occipital lobes can also be divided into quarters, left and right, upper and lower, corresponding to a quadrant of the visual field.
So, looking at our quadrants, we see that each can be affected in different ways by different processes in different parts of the brain.
The same information is shown in this diagram (above). The quadrants of the visual field and the corresponding parts of the occipital lobes are matched by using the same colours, for example the upper left visual field is pink, as is the corresponding lower right occipital lobe.
The white wriggly arrows (highlighted below) represent the optic radiations as they pass through the temporal lobes and the back of the parietal lobes.
As with all visual field impairments, the area with reduced or absent vision needs to be identified, and the areas where vision is best, used.
It can be easy for a person to forget they have a visual field impairment, because it is not something they are consciously aware of, especially when they are tired or distracted.
Think of safety. Where one of the upper quadrants is affected, it can be easy to bump into something that is low hanging. Where the lower quadrants are affected, it can be easy to not see and trip over low things.
For children at school, ensure all their work is positioned where they can see it. If part of their work-page is absent due to quadrantanopia they may not be aware of it, and as a result their work may not make sense. This can look like reading or learning difficulties (see Visual Behaviours, below).
It is very easy to forget one has a quadrantanopia, and just because the rest of the picture is present, it does not mean the person magically knows what is in the absent quarter.
How many people are in this meeting (image below)?
If the person can't see something due to quadrantanopia...they can't see it!
This may make the person affected sometimes seem:
Quadrantanopia can easily go undetected. So these difficulties might seem unexplained or considered the fault of the affected person, when it is not.
Some may only have vision in one quadrant. This can occur for example if a child has both a severe lower visual field impairment (lesson 6d) and upper (superior) quadrantanopia, due to damage to both posterior parietal lobes and one temporal lobe.
Where there is more than one visual field impairment, it indicates more extensive damage to the brain. This can be present in some of the more profoundly affected and disabled children, including those with cerebral palsy. Many may be thought of as being completely cortically blind (which we will explain in lesson 6g), with occasional intermittent visual responses.
When vision is present in only one quarter of the visual field, it is easy to miss.
Visual field testing can identify an area of better vision, even in the most complex child. Once identified, this area of vision can be used to help the person learn.
Looking at the image above, what is it? Vision in only one quadrant is difficult to make sense of. It is confusing and could even be frightening. If an area of vision is identified it can create an incredible learning opportunity.
Before moving on to the next lesson please check you understand:
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