Neurological Vision Disorders
Our eyes, by detecting light, deliver information on the world around us to various parts of the brain via nerves. The occipital cortex, situated at the rear of the brain, processes the information and allows us to ‘see’ distance, shape, movement and colour.
Vision impairment resulting from an acquired brain injury (also called ABI VI) is vision loss caused by damage to the areas of the brain that are responsible for sight. The many causes of ABI VI can include stroke, brain tumour, head injury and infections such as meningitis.
The type and severity of vision loss depend on which area of the brain was affected and to what degree. In some cases, the impairment may improve with time - for example, children with ABI VI tend to experience improvement as they grow older. Other (outdated) names for ABI VI include cortical visual impairment and cortical blindness.
Some of the many causes of ABI VI
- Stroke, or ‘brain attack’, where part of the brain is damaged by haemorrhage or blockage in a blood vessel of the brain.
- Traumatic brain injury - for example, following a car accident or fall.
Infection, such as meningitis or cytomegalovirus.
- Lack of oxygen, such as near-drowning, or a heart attack which can interrupt the flow of blood to the brain.
- Disease, such as a brain tumour or multiple sclerosis.
Some of the different kinds of vision impairment caused by brain injury
- Visual field defects - such as homonymous hemianopia, when one half of the visual field in each eye is missing.
- Double vision - or diplopia. The muscles of both eyes can’t coordinate their movements, so the two images fail to merge properly.
- Fluctuating vision - this means the impairment is variable; for example, the person may be able to see something one day, but not the next. This is more common in people who also have seizure disorders.
- Visual acuity problems - difficulties with seeing clearly or interpreting what is seen.
- Eye movement problems - for example, jittery eye movements or the tendency of the eyes to flicker around when the person is trying to look steadily at something (nystagmus).
- Strabismus - or squint. One eye (or both) is unable to align properly; for example, it may turn inwards or outwards.
Glasses or contact lenses won’t help because the cause lies in the person’s brain, not their eyes. Treatment involves managing the symptoms, and depends on the type of vision impairment and its cause.
Options may include:
- Treating the underlying brain injury. If the brain can recover from its injury, the person’s vision may also improve.
- Wearing an eye patch - this can help in the case of double vision. It is important to alternate the patch so that each eye gets equal time.
- Strabismus can be treated by patching the good eye, which forces the muscles of the turned eye to work harder and get stronger.
- Options for managing poor visual clarity include using large print, writing with felt-tipped pens and good lighting.
- A person with a visual field defect can learn to use their eyes and/or head in a ‘scanning’ fashion, which means moving the eyes back and forth to make sure they see the objects in their blind spot.
- Special programs, such as the Acquired Brain Injury Mobility Service provided by Guide Dogs Victoria, are available to people with ABI VI.