The Vision Impact Survey for Keratoconus (VISYKO) for measuring the quality of life in patients with keratoconus

Purpose To assess the psychometric properties of the Vision Impact Survey for Keratoconus (VISYKO) as a patient- reported outcome (PRO) to measure the vision-related quality of life (QoL) in keratoconus patients. Setting University of Florence, University of Siena, Studio Italiano di Oftalmologia Methods 130 patients with keratoconus and 131 age- and refractive error-matched healthy subjects, completed the VISYKO. Rasch partial credit model (PCM) analysis was applied to validate VISYKO, and QoL scores were compared between patients and controls and across different disease severities classified using Amsler-Krumeich grading (1 to 4). Model fit and item fit were also assessed. Results Rasch PCM analysis supported VISYKO’s validity in assessing vision-related QoL scores in keratoconus patients, with composite scores significantly higher (P<0.001) in patients (32.8±18.7 a.u.) than controls (13.7±14.1 a.u.). VISYKO scores significantly discriminated between early and advanced disease stages, rising from 23.8±16.3 a.u. in grade 1 to 48.1±18.7 a.u. in grade 4 (P=0.01). The survey was also able to discriminate among patients who had (28.7±17.1 a.u.) or did not have (38.5±19.4 a.u.; P=0.003) corneal cross-linking (CXL) treatment. Confirmatory factor analysis showed excellent model fit, with indices of 0.98. Conclusions The VISYKO met the formal requirements for PRO measurement. It is a reliable, well-constructed, and keratoconus-specific tool with high psychometric validity. VISIKO differentiates QoL impacts across different severity stages and assesses the effect of CXL treatment. Conflict of interest: None declared