Development and initial validation of an assessment of visual ability for children with cerebral palsy

BACKGROUND Children with cerebral palsy have a primary motor disorder that may be accompanied by disturbances of sensation or perception that impact their ability to use vision. Many other factors may also influence how a child ‘uses their vision’, yet our understanding of how to optimise outcomes rarely includes a focus on visual abilities. For some children with cerebral palsy, visual ability may be a strength. To maximise a child’s ability to use vision we first need a method to quantify visual ability. This thesis describes the conceptualisation, development, and initial validation of a scale to describe ‘how vision is used’ by children with cerebral palsy.

METHODS Using a multi-phase mixed methods instrument project design, the first step was a systematic review to identify and appraise existing measures. This was followed by a study to map items from existing measures to the International Classification of Functioning, Disability and Health (ICF) framework using standard linking methodology. After confirming the need for a new measurement tool, the second phase of this research involved an international online survey of key stakeholders; the construction of items and a rating scale; and pre-testing with cognitive interviews. The third phase explored the psychometric properties of the tool in initial field testing.

RESULTS The systematic review confirmed a gap in assessment practices for describing ‘how vision is used’. The mapping exercise led to the conceptualisation of visual ability as a measurable construct at the Activity level of the ICF, and observable visual behaviours were identified to describe how vision is used. Findings from the stakeholder survey contributed to evidence of the relevance and comprehensiveness of content, whilst also defining what is not the focus of the measure: child factors (e.g. eye functions), environmental factors (e.g. type of visual information), or performance and participation in vision-related activities (e.g. play). The primary outcome of this research, the Measure of Early Vision Use (MEVU), is a 14-item parent-report questionnaire describing a child’s ability to use vision. Each item is an observable visual behaviour, scored on a 4-point ordinal scale. Psychometric data from field testing (n=100) supports MEVU as a unidimensional scale with good internal consistency, sufficient construct validity, and feasibility as a parent-completed online assessment.

CONCLUSION MEVU is a new instrument to describe the use of basic visual abilities that has potential to support early intervention planning for children with (or at high risk of) cerebral palsy.