Validity of a visual impairment questionnaire in measuring cataract surgery outcomes

Abstract

Purpose: To test the validity of the Impact of Visual Impairment (IVI) questionnaire in a cataract population. Setting: Flinders Eye Centre, Flinders Medical Centre, Flinders University, Adelaide, South Australia. Methods: Cataract patients recruited from a hospital waiting list completed the IVI questionnaire. The scale was assessed for fit to the Rasch model. Unidimensionality, item and person fit to the model, response category performance, differential item functioning (whether different subgroups responded differently), and targeting of item difficulty to patient ability were assessed. Results: Overall, the IVI questionnaire performed well; there were ordered thresholds, person separati..