Translation, Evaluation and Validation of the Adult Strabismus -20 (AS-20) Questionnaire in Swedish.

Purpose: To translate and validate the Adult Strabismus 20 (AS-20) questionnaire, a health-related quality of life questionnaire specifically devised for patients with strabismus.

Methods: The AS-20 was translated in accordance with the principles of good practice for the translation and cultural adaptation process for patient-related outcomes (PRO) according to the methodology recommended by the International Society for Pharmacoeconomics and Outcome Research (ISPOR). The translation, evaluation, and validation were performed in several steps. The study used both qualitative and quantitative methods and engaged 31 final-year orthoptic students in workshops, as well as 19 experts (experienced clinical orthoptists), 17 laymen (members of the public), and 17 patients from national eye clinics. The final translated questionnaire was tested for reliability and validity in 68 adults with strabismus by internal consistency using Cronbach´s alpha and content and construct validity using the Rasch analysis.

Results: The Swedish AS-20 showed a high level of internal consistency. Cronbach´s alpha was 0.95 for the psychosocial subscale and 0.92 for the functional subscale. However, the Rasch analysis indicated that both items and responses should be condensed to achieve content and construct validity.

Conclusion: The thorough translation and evaluation process resulted in a validated AS-20 questionnaire for use in the Swedish language, and shows reliability as an instrument to measure health-related quality of life (HRQoL) in adults with strabismus in a clinical setting.