Responsiveness and minimal important change of the Dutch Adult Strabismus-20 Questionnaire (Dutch-AS-20)

The Dutch Adult Strabismus-20 questionnaire (Dutch-AS-20) is a patient-reported outcome measure (PROM) developed to assess the strabismus-specific quality of life (QoL) in adult patients with strabismus in the Netherlands. This 18-item questionnaire comprises a psychosocial and visual function subscale. The aim of this prospective, multicenter, longitudinal study was to evaluate the responsiveness and determine the minimal important change (MIC) of the Dutch-AS-20 in patients undergoing strabismus surgery.

Adult patients scheduled for strabismus surgery were enrolled. The Dutch-AS-20, EQ-5D-5L, Amblyopia and Strabismus Questionnaire (A&SQ), Diplopia Questionnaire (DQ) and two global rating of change (GRC) questions were administered pre- and/or postoperatively. We used a construct approach to assess the responsiveness, testing eight pre-specified hypotheses. We determined the MIC using adjusted anchor-based predictive modelling.

A total of 136 patients completed the questionnaires at baseline. All pre-specified hypotheses were met, indicating sufficient responsiveness of both subscales of the Dutch-AS-20. We estimated a MIC of 3.1 T-score points for the psychosocial subscale. We could not estimate the MIC for the visual function subscale due to a low correlation with the GRC question.

Both subscales of the Dutch-AS-20 are sufficiently responsive to change in strabismus-specific QoL following strabismus surgery. These findings are an important step towards the use of the Dutch AS-20 in both research and clinical practice. Future research is needed to determine a more precise MIC and individual-level statistics for both subscales, in order to improve the interpretability of change scores for both clinical and research purposes.