Factors Affecting the Test Situations
When observing or assessing a certain visual function the tester needs to be aware of other functions that may not be normal and that may interfere with the child's performance in a task. In a number of test situations the expected response is a motor response, following movement or a quick saccade. To perform such a motor response depends on several prerequisites:
- the child is able to direct attention to the test stimulus
- the child can plan following movements or saccades
- the child has the motor functions to execute the plan
- the test stimulus is within the visual field of the child
- the test stimulus is presented within the visual sphere of the child
- the position of the child does not inhibit the response
These prerequisites are especially important in all preferential-looking situations. The size and quality of the visual field need to be known. Otherwise we might interpret a weak response as a result of poor attention. Attention and motivation to look at a stimulus vary even within a normal visual field: objects with high contrast, bright colour or shining surface often cause a stronger response than some less visible objects. However, large low contrast pictures in motion often seem to effectively interest infants and young children.
These prerequisites are especially important in all preferential-looking situations. The size and quality of the visual field need to be known. Otherwise we might interpret a weak response as a result of poor attention. Attention and motivation to look at a stimulus vary even within a normal visual field: objects with high contrast, bright colour or shining surface often cause a stronger response than some less visible objects. However, large low contrast pictures in motion often seem to effectively interest infants and young children.
The type of fixation needs to be known. If a child has eccentric fixation, he seems to look past the stimulus when looking at it. Some children have roving eye movements without stops for fixation. It may be necessary to use video films for more careful observation on what the child has been looking at. If a child has strabismus it may be difficult to know which eye is used for fixation. In that case covering one eye at a time may solve the problem. If eye movements are irregular, it is advisable to discuss with the child's ophthalmologist their effect on the test situations.
Since a child's way of fixating may change over time it should be described in each report and recorded on video when possible.
[ Instructions I Paediatric Vision Tests I Vision Tests ]
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