Validation of the Croatian Visual Function Classification System and subtype-specific differences in cerebral palsy

The Visual Function Classification System (VFCS) provides a standardised framework for grading visual functioning in children with cerebral palsy (CP). This study evaluated the reliability and construct validity of the Croatian VFCS, and its ability to distinguish visual functioning across CP subtypes and functional classifications. Ninety-five children with CP (mean age: 11.8 years, range: 4-18) were assessed using VFCS, Gross Motor Function Classification System (GMFCS), Manual Ability Classification System (MACS), and Communication Function Classification System (CFCS). Reliability was tested using quadratic weighted kappa and intraclass correlation coefficients (ICCs); differences across CP types with the Kruskal-Wallis, and construct validity with Spearman correlations. The Croatian VFCS showed excellent interrater ( κ = 0.87) and intrarater reliability ( κ = 0.92), with ICCs greater than 0.90. VFCS levels differed significantly by CP subtype ( χ ² = 8.30, P = 0.016), with preliminary evidence suggesting that unilateral spastic CP may be associated with better visual function than bilateral spastic or dyskinetic CP. Moderate correlations with CFCS ( ρ = 0.557), MACS ( ρ = 0.392), and GMFCS ( ρ = 0.308) revealed clinically relevant divergences between visual and motor abilities. The Croatian VFCS is a reliable, valid, and clinically sensitive tool. This study provides preliminary evidence of its discriminative utility across CP subtypes and supports integrating VFCS into multidisciplinary assessment and individualised rehabilitation planning.