Abstract
PURPOSE: This study aims to develop an item-bank to measure vision-related quality of life (Vr-QoL) and subsequently calibrate this set of items. METHODS: Three Vr-QoL instruments were searched for suitable items to be added in the EyeQ. Patients who received antivascular endothelial growth factor treatment for various retinal diseases involving macular edema were included in the study and completed the 47-item EyeQ. Item response theory (IRT) was used to calibrate the EyeQ items, which was performed multiple times in subsets as a novel approach, containing 80% of the data. Differential item functioning (DIF) was evaluated for various variables. RESULTS: Responses of 704 patients were used in analysis. One item violated the local independence IRT-assumption and showed a high percentage of missing values, after which this item was deleted from the item-bank. The data of the five subsets fitted the graded response model adequately, and no DIF was detected for items between subsets, after which mean item parameters were calculated. Item fit statistics were found to be good. DIF was detected for gender, age, and administration mode by the patient (independently vs. with help), this involved three items, which all showed negligible impact on total scores. CONCLUSIONS: Because of separate calibrations of the EyeQ in multiple subsets, a high robustness of item parameters is expected. TRANSLATIONAL RELEVANCE: The calibrated EyeQ can now be used for the assessment of Vr-QoL in patients suffering from exudative retinal diseases and is promising for use as a computer adaptive test.