Video Link: https://vimeo.com/589918053

Imagine that the image below represents a full visual field.

With visual field constriction, only a small island in the centre is visible.

Compared to the representation of a full visual field (above), the affected person may only be able to see a small amount, as illustrated below.

Looking at the images side by side, below, we can see that visual field constriction can be a marked visual impairment.

The size and shape of the visual field constriction will vary from person to person.

The person with a visual field constriction is not aware of the large area of their visual field where they have no vision. Their visual world is the small island.

Visual field constriction as a cerebral visual impairment is quite rare.

It is caused by a brain injury affecting both occipital lobes. The commonest cause is a stroke. This can occur at any time, and can happen in all age groups including the developing foetus.

If, during a stroke there is a secondary supply of blood to the area of the brain affected, here the occipital lobes, then a small section may be spared, because it continues to get a supply of oxygen from this other source. This is why visual field constriction due to this cause is also sometimes called central sparing.

With visual field constriction, an MRI scan is likely to show considerable damage to the occipital lobes and/or the visual pathways to them. If the occipital lobes do not show evidence of damage, then it is likely that the narrow central island of vision may be due to lack of peripheral visual attention, which is more likely to be variable in nature, as explained in the video tutorial, or a range of disorders of the retina, or glaucoma affecting the optic nerves, or damage to where the optic nerves join, called the optic chiasm.

There is a further rare cause previously called 'hysteria', but now called functional visual impairment. In medical terms, when something is due to functional visual impairment it means that no known physiological or biological cause can be found, and the cause is considered the persons 'state of mind' or emotional state. An internet search of 'hysterical / functional visual impairment' will show many research publications on the subject.

Islands of Vision - Different Cerebral Causes

Visual Field Constriction & Simultanagnostic Vision

Some people are severely affected by simultanagnostic vision, as explained in lesson 3g and explain further in lesson 7c. We have heard it described as like seeing life looking through a drinking straw. In some cases, simultanagnostic vision can be misdiagnosed as visual field constriction.

Visual field constriction is very unusual in children with cerebral visual impairment.

Simultanagnostic vision is much more common.

• Question: Why does it matter what name we use, if both mean only a small island of vision?

With visual field constriction, the island of vision remains consistent; the same size in the same part of the visual field. With simultanagnostic vision, as we explain in Level 9, the area of vision can vary, and targeted support to recognise and deal with the causes of this can be enormously helpful.

• Question: Why does it matter what name we use, if both mean only a small island of vision?
• Answer: Because they are two different conditions, requiring different approaches to support.

Targeted Support

For those with visual field constriction the area of visual loss is consistent. So support strategies including technical aids and mobility training, for example in the use of a cane, can be helpful. While for those who have the attentional visual field constriction related to impaired functioning of the posterior parietal lobes causing 'dorsal stream dysfunction', measures to minimise crowding, clutter and distraction are the order of the day.

Checklist:

Before you move onto the next lesson, please check you understand:

• What visual field constriction means
• A cause of visual field constriction
• Why visual field constriction is sometimes called 'central sparing'
• Other conditions creating an 'Island of Vision'
• The importance of the correct diagnosis (in relation to visual field constriction).

Next lesson: Level 6g CVIs Visual Field Impairments - Complete Absence of Vision