Evaluation of the German Version of the Keratoconus Outcomes Research Questionnaire

Purpose: To translate, validate, and evaluate the psychometric properties of the German version of Keratoconus Outcomes Research Questionnaire (KORQ). Methods: This prospective study included 3 phases. In phase 1, the KORQ was translated in a standardized way; in phase 2, Rasch validation was performed; in phase 3, the validated questionnaire was evaluated in a separate patient cohort. All patients answered the German KORQ. Scheimpflug imaging (Pentacam) and optical coherence tomography scans (MS-39) were conducted. Corneal imaging measurements were correlated with patient-reported outcome measures. Results: After standardized translation, 100 patients self-administered the German KORQ. Rasch analysis was conducted for psychometric testing of the KORQ. Based on the results of the Rasch analysis, the original German version of the KORQ was modified and any items showing a misfit were excluded. This resulted in a new shortened version of the KORQ, which was evaluated in 30 patients. The revised German KORQ met the criteria of Rasch analysis and showed excellent internal consistency reliability and convergent validity. The correlation between the KORQ score and various clinical measurements was examined using Spearman correlation. A significant moderate correlation was observed between the D (r = 0.237; P = 0.006) and K max (r = 0.162; P = 0.065) values of Pentacam. Inverse correlations were observed for thinnest pachymetry measured with MS-39 (r = −0.167; P = 0.058) and best corrected visual acuity (r = −0.210; P = 0.016). Conclusions: The shortened German KORQ met the assumptions of the Rasch model and displayed satisfactory psychometric properties. The German KORQ could be adopted as a powerful patient-reported outcome measures tool for German-speaking patients with keratoconus in the future.