Prescribing Assistive Technology for Users with Cortical Visual Impairment

Prescribing Assistive Technology for Users with Cortical Visual Impairment

As clinicians, we always consider visual impairments when assessing for and prescribing assistive technology, but if we’re honest we often treat visual impairments as a homogenous group rather than considering the specific type of visual impairment an individual may have. Considering that there are many types of visual impairments which present differently and have varying impacts on assistive technology use, it’s vital that as clinicians we find out what type of visual impairment our clients present with to ensure the optimal outcome of the assistive technology assessment process.

One of the common visual impairments our clients may have is Cortical Visual Impairment (CVI). CVI is the result of neurological damage, rather than injury to the eye structures itself1. CVI is usually the result of damage to the posterior visual pathways, and/or the occipital lobes of the brain1. Most visual impairments resulting from damage to the eye structures influence the quality and clarity of a visual image to varying degrees, while CVI affects the brain and its ability to process visual information in addition to the quality of the visual image1. Essentially, CVI affects the processing and perception of what is seen1.

The causes of CVI include insufficiency of oxygen (anoxia, hypoxia, ischaemia, and asphyxia), developmental brain anomalies, brain injury, cerebral palsy, hydrocephalus, and infections of the central nervous system such as encephalitis and meningitis2. It is estimated that 29% of individuals with CVI also have a cognitive impairment and 56% of individuals with CVI also have other disabilities3. As vision provides vital feedback to the vestibular and proprioceptive systems, motor development can be negatively affected in children with CVI3.

Certain characteristics are common to individuals with CVI. A significant characteristic is fluctuation in visual functioning, where the individual may be more visually aware on one day or in one hour than the next2. This often coincides with fluctuations in level of attention2. People with CVI can have difficulty noticing things in their lower visual field and have better vision in their peripheral vision3. Individuals with CVI may appear to look at an object of interest and then look away when reaching for it2, or may bang a tray or desk to try and move items into their visual field3.

We know that vision is a multi-step process. For example, the process for catching a ball involves:

  • seeing the ball
  • identifying it
  • distinguishing it from other objects
  • choosing to follow it
  • predicting its future path of motion
  • planning what movements are needed to reach the ball
  • moving to catch the ball3.

The same analysis can be applied to an assistive technology task, like controlling a power wheelchair to move towards a toy across the room (this is where those activity analysis skills come in handy). This process would involve:

  • seeing the toy
  • distinguishing it from other objects
  • identifying it as desirable
  • choosing to move towards the toy
  • identifying that the power wheelchair can provide the means of movement towards the toy
  • seeing the power wheelchair controls and identifying their role in movement
  • distinguishing the controls from surrounding objects
  • moving the part of the body that controls the wheelchair to the controller (be in the hand, chin, head or other body part)
  • planning the movements and direction of travel needed to reach the toy
  • moving the wheelchair controls in that direction and safely controlling the wheelchair
  • stopping once the toy is reached
  • reaching to pick up the toy

When we break down a task we can see how complex a task can be and how CVI can impact on the ability to successfully complete those steps. But there are some simple things we can do as clinicians to promote successful use of assistive technology. One of the most beneficial things we can do is simply consult an expert on the individual’s vision, including the family and carers, medical practitioners and specialist allied health clinicians, especially if the individual works with allied health professionals that specialise in vision.

When setting up assistive equipment for a person with CVI, consider the overall environment. Individuals with CVI often perform better visually when activities have minimal clutter and external distractions such as noise are removed2. If using a wheelchair control or a switch, consider positioning it where the individual’s vision is best, such as in their peripheral vision3. People with CVI often prefer one colour, usually primary colours like red that are high contrast, so consider using stickers or certain colour switch covers. If teaching powered mobility skills, consider blacking out the environment (such as black curtains or paper on walls) and then providing one piece of red stimulus on the wall as a guide for movement and direction). You could also black out the area around the wheelchair controller or switches, and highlight the controller or switches in red to direct visual attention to it.

Individuals with CVI can find movement very helpful when trying to locate and track objects. Movement, especially movement at the periphery of our vision, alerts the brain and many people with CVI can see better when they are moving or the object is moving3. A slight bounce can draw attention to an object, but slow movements are more beneficial than fast movements3. It can be helpful to provide prior instruction of what the individual should be looking for2, as well as giving plenty of quiet time to process any instructions (up to around 20 seconds)3.

Assessing and prescribing assistive technology with individuals with CVI can be challenging, but with the right support team and techniques in place the process can be successful. Our GTK Consultants are always enthusiastic about being a part of that support team – contact us today to see how we can help.

 

References
  1. Wright, Rosa (2016). Cortical Visual Impairment. RIDBC, available from https://ridbc.org.au/vision-services/ridbc-vision-resources/cortical-visual-impairment-cvi-ibook/
  2. Vision Australia. Cortical Visual Impairment [PDF file]. Retrieved from https://www.visionaustralia.org/sites/default/files/docs/default-source/eye-health/Fact-sheets/cortical-visual-impairment-factsheet_v2-web-(accessible).pdf?sfvrsn=0
  3. Petito, C. (2017, March 3). Assessing Mobility for Those with Cortical Vision Impairment [Conference presentation]. International Seating Symposium, Nashville, TN, United States.