Piloting Rasch model scoring of the National Eye Institute Visual Function Questionnaire in uveitis.

INTRODUCTION: The National Eye Institute Visual Function Questionnaire (NEI VFQ) is a common patient-reported outcome measure (PROM) in uveitis trials. Its psychometric properties using state-of-the-art scoring based on Rasch models, a latent trait model that improves accuracy of PROMs assessment, has not yet been investigated.

METHODS: The study participants were recruited online from uveitis patient organizations, where individuals self-reported their uveitis diagnosis and visual acuity level. These participants then completed the NEI VFQ-25. The visual function (VF) and socioemotional (SE) subscales were psychometrically analysed in terms of item fit, targeting, internal consistency, dimensionality, and differential item functioning (DIF), using Rasch models. Criterion validity was examined based on associations between NEI VFQ person measures and recent visual acuity (VA) levels.

RESULTS: Ninety-nine participants recruited online from uveitis patient organizations (68 women, 31 men; mean age 50 ± 15 years; 46.5% self-reported receiving systematic therapy for uveitis, 0.6% NEI VFQ-25 missing data) were included. The mean difficulty of items was lower than the average person ability. None of the items demonstrated misfit to an extent that would induce noise into the measurement. The consistency metrics person reliability and person separation index of the subscales were 0.85 and 2.34 (NEI VFQ-VF), 0.86 and 2.52 (NEI VFQ-SE), respectively. There was no evidence of multidimensionality and none of the items showed DIF by gender. The differences between item and person measures were 1.44 (NEI VFQ-VF) and 1.03 (NEI VFQ-SE). NEI VFQ-25 person measures were significantly lower in participants with visual impairment (all p values ≤ 0.007).

CONCLUSION: Rasch model-based scoring of the re-engineered NEI VFQ-25 demonstrates acceptable internal consistency, item fit and construct validity for assessing two key domains of quality of life in individuals self-reporting uveitis. The PROM was targeted at a higher level of difficulty than present in our heterogeneous sample.