Translation, cross-cultural adaptation, and validation of the Norwegian version of the Keratoconus Outcomes Research Questionnaire.

Purpose: To translate and adapt the Keratoconus Outcomes Research questionnaire (KORQ) to Norwegian language, culture, and environment, and to validate the translated version in a Norwegian population with keratoconus.

Methods: KORQ was translated to Norwegian using a multi-step methodology. Persons with keratoconus submitted responses to KORQ-NO and NEI VFQ-25 through a digital platform, and a retest of KORQ-NO was performed over the telephone. Additional data from a clinical intervention study was included. The psychometric properties of KORQ-NO were assessed by Rasch analysis. Test-retest reliability, construct validity, and responsiveness were explored by Intraclass Correlation Coefficients, Spearman correlations and Wilcoxon Signed-rank test.

Results: KORQ-NO and NEI VFQ-25 were completed by 165 participants with keratoconus. With few adjustments, the "Activity limitations" (AL) and "Symptoms" (S) subscales of KORQ-NO exhibit acceptable psychometric properties with good model fit, high internal reliability, and well-targeted items to the population. Deletion of four items (AL3, AL3b, AL12, AL15) improved dimensionality of the "Activity limitations" subscale. Differential item functioning was present in two items (AL4 and AL6). Participants and optometrists confirmed content validity, and KORQ-NO exhibited good test-retest reliability (AL ICC = 0.90 and S ICC = 0.81), construct validity, and responsiveness.

Conclusions: Successful translation and adaptation of KORQ to Norwegian language, culture and environment was confirmed by acceptable psychometric properties, with good validity, reliability, and responsiveness. The authors support the use of KORQ-NO in research, clinical practice, and as documentation for national insurance benefit applications.