Psychometric properties of the National Eye Institute Visual Function Questionnaire (NEI-VFQ 25) in a Norwegian population of patients with neovascular age-related macular degeneration compared to a control population

BACKGROUND: Although visual acuity and optical coherence tomography (OCT) are most widely used as outcomes in treatment of neovascular age-related Macular Degeneration (nAMD), patient reported outcome measures are increasingly recognized. National Eye Institute Visual Function Questionnaire (NEI-VFQ 25) was developed to capture the perceived visual function. Yet, evidence of psychometric performance in the target population is required. The aim of this study was to examine the psychometric properties of NEI-VFQ 25 in a Norwegian cohort of newly diagnosed nAMD patients followed with a Treat and Extend (T/E) protocol. METHODS: Patients receiving intravitreal anti–vascular endothelial growth factor (anti-VEGF) injection treatment according to a T/E protocol completed a Norwegian translation of NEI-VFQ 25, EuroQoL Health Questionnaire (EQ-5D), and Patient acceptable symptom state (PASS 5) at baseline, 3, 6 and 12 months. In addition, a control population completed the same questionnaires. Visual acuity was assessed with LogMar for best/treated eye. Validity testing comprised face validity by a 0–10 numeric rating scale about relevance of NEI-VFQ 25 as well as regression analyses and correlations between NEI-VFQ 25 and other relevant variables. Reliability was examined with Intraclass Correlation Coefficient (ICC) and Cronbach’s alpha for internal consistency were performed. Responsiveness, discriminatory power and predictive value were also explored. RESULTS: Number of respondents at baseline, after 3, 6 and 12 months was 197, 186, 176 and 168, respectively. The control population comprised 26 individuals. Face validity of NEI-VFQ 25 had a mean (SD) of 7.8 (1.7) (n = 84). NEI-VFQ was significantly correlated to visual acuity and PASS 5 as well as EQ-5D at baseline. Reliability (ICC) of the overall and sub scores for the patients/controls ranged from 0.49–0.97/0.59–0.97. Cronbach’s alpha was 0.61–0.85. Discriminatory power was confirmed by significant differences of the overall score between controls and patients (P < 0.001). NEI-VFQ 25 indicates responsiveness showing overall score improved significantly (P ≤ 0.001) from baseline to 3 months. NEI-VFQ 25, general health and visual acuity at baseline were the strongest predictors for how patients reported vision after 6 months follow-up. CONCLUSION: NEI-VFQ 25 showed acceptable psychometric performance, which supports that the Norwegian version can be used to monitor patients treated for nAMD.