Translation and Testing Psychometric Properties of the Thai Version of Vision Bolt-On EQ-5D in Patients With Visual Impairment

This study aimed to translate, culturally adapt, and evaluate the psychometric properties of the Thai versions of the vision bolt-on EQ-5D-3L and EQ-5D-5L, comparing them with the standard EQ-5D-3L, EQ-5D-5L, and EQ-VAS in individuals with varying degrees of visual impairment. Following EuroQol Translation Guidelines, the vision bolt-on items were translated through forward-backward processes and underwent cognitive debriefing. A total of 301 participants were interviewed at baseline, with 275 completing a 2-week follow-up. Known-groups validity was assessed based on visual acuity classifications and comorbidity status; convergent validity was tested by using Spearman's correlations. Test-retest reliability was evaluated with intraclass correlation coefficients (ICCs) and weighted kappa. Responsiveness was analyzed using a standardized effect size in participants who reported better or worse vision. Both versions of the vision bolt-on had no missing data and demonstrated moderate to good test-retest reliability (ICC range 0.62-0.64). They effectively differentiated quality-of-life scores across varying degrees of vision impairment, showing reduced ceiling effects (5%-9%) compared with the standard EQ-5D. Correlations with EQ-VAS were moderate (rho 0.40-0.45). When participants reported improved vision, the vision bolt-on EQ-5D-5L exhibited the highest responsiveness, whereas all instruments were generally less responsive for worsening vision. The Thai versions of the vision bolt-on EQ-5D-3L and EQ-5D-5L demonstrated acceptable reliability, validity, and moderate responsiveness for capturing vision-related health changes, with the 5L version showing slightly greater sensitivity. These findings support the usefulness of adding a vision dimension to EQ-5D for Thai-speaking populations, facilitating more precise evaluations of interventions targeting visual health.