CAUSES
Causes of CVI can include:
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Asphyxia;
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Stroke;
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Traumatic brain injury;
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Infection (such as meningitis or toxoplasmosis); and
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Tumour.
CVI can coexist with ocular vision impairment.
DIAGNOSIS
If you believe you or a family member may have CVI, you may like to talk to your regular health care provider who may suggest referral to an ophthalmologist and other medical and allied health professionals who can provide support.
CVI is indicated when all the following characteristics exist:
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An ocular eye exam that is normal or cannot explain the functional vision impairment;
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A history of a significant congenital or acquired brain injury or neurological disorder; and
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The presence of unique visual characteristics and behaviours associated with CVI.
CHARACTERISTICS
Each child and person with CVI is unique in the way they perceive the world around them. There are 10 common characteristics and behaviours that may be present in children with CVI. These characteristics may appear to fluctuate depending on the complexity of the surrounding environment.
COLOUR PREFERENCE
Many children with CVI show a strong colour preference by visually attending to objects of a certain colour.
VISUAL LATENCY
Visual latency is when there is a delayed response to look towards a visual target. These delays can be significant, up to 20 seconds or more.
VISUAL COMPLEXITY
Visual complexity involves three parts:
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The pattern or complexity of an object itself;
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The visual background surrounding the object (i.e. the visual array);
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The total sensory environment.
Children with CVI may become overwhelmed and unable to process what they are seeing depending on visual and sensory complexity. Sensory complexity includes any other competing sensory input such as sound or touch, and it also includes physical (postural) demands and fatigue.
DIFFICULTY WITH DISTANCE VIEWING
As objects are further away, they become a smaller part of the overall picture, and may not be as easily discriminated.
Distance viewing is associated with visual array complexity. The closer an object is when viewed, the less cluttered the background appears to be.
NEED FOR MOVEMENT
Children with CVI often respond best visually to shiny and reflective objects, or objects that move.
DIFFICULTY WITH VISUAL NOVELTY
Children with CVI may have difficulty visually attending to unfamiliar objects, showing preference for familiar objects that are of a particular colour or pattern.
VISUAL FIELD PREFERENCE
Many children with CVI have strong visual field preferences (e.g. left or right side, or upper visual field).
NEED FOR LIGHT
Children with CVI may stare at light sources for extended periods of time.
ATYPICAL VISUAL REFLEXES
There are two visual reflexes:
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One is where the child blinks simultaneously to a touch at the bridge of the nose.
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The second reflex is when they blink as a visual threat (e.g. an open hand) moves quickly towards the face at midline. A child with CVI commonly presents with absent or delayed visual reflexes.
ABSENCE OF VISUALLY GUIDED REACH
Visually guided reach refers to the ability to look at and reach for an object simultaneously. A common pattern seen in many children with CVI is to look toward an object, look away, and then reach for it.
PHASES
There are three phases of CVI. The goal of intervention is to assist children to move through the three phases so they can reach their maximum potential.
PHASE ONE
In Phase One, the individual is using vision infrequently. The focus of intervention is building visual behaviour so they become more consistent in looking at a small amount of specific objects that you use every day.
This may involve using objects of a preferred colour such as a spoon during feeding time, or a mobile placed above their change table.
PHASE TWO
Here, the child is starting to use vision to indicate a want or need by looking or reaching toward an object or person. The focus of intervention is integrating vision with function. In Phase Two, the use of vision has become active.
This may involve practicing tracking an object in a preferred colour and visual field, and reaching for it. Remembering the 10 characteristics of CVI, a carer can learn to adapt the child’s environment and position to help them develop in this phase.
PHASE THREE
In Phase Three, we are working toward refinement of the CVI characteristics. This might also be thought of as fine-tuning vision, especially in complex environments.
While it may appear that some characteristics of CVI are resolving in this phase, it remains a critical phase to ensure children are understanding what they see. Using salient features to describe surroundings, and providing appropriate support and tools are very important at this stage.
ASSESSMENT
Any child who has a diagnosis of CVI from an ophthalmologist or other medical specialist should have their functional vision assessed using the CVI Range.
If a child does not have a diagnosis but has sustained brain or neurological damage and is displaying the visual behaviours and characteristics associated with CVI, a functional vision assessment using the CVI Range is still recommended. If you believe you or a family member may have CVI, you may like to talk to your regular health care provider who may suggest referral to an opthamologist and other medical professional to confirm the diagnosis.
How CVI is assessed
The CVI Range assesses for both the presence and the impact of each of the visual characteristics and behaviours described above. This information is collected through:
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An interview with parents and educators,
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Observation of the child in the home and education settings, and
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Direct assessment of the child.
Information from all three elements are used to determine a CVI Range ‘score’. From this score, the child is assessed at being at one of three phases of CVI. This information is used to determine appropriate intervention for the child.
Interventions are individual but providers may also help to connect you with other families and professionals.