The Impact of Vision Impairment for Children (IVI_C): validation of a vision-specific pediatric quality-of-life questionnaire using Rasch analysis.

PURPOSE: To validate the Impact of Vision Impairment for Children (the IVI_C), a new vision-specific pediatric instrument designed to assess the affect of impaired vision on quality of life (QoL) in children.
METHODS: The IVI_C was administered to vision-impaired and normally sighted students, 8 to 18 years of age. Reliability and validity were tested, and the IVI_C was subjected to Rasch analysis to assess the scale unidimensionality, measurement characteristics, response options, and targeting.
RESULTS: The mean (SD) presenting bilateral distance visual acuity (VA) for the vision-impaired group (n = 122) was 1.10 (0.79) logMAR and 1.15 (0.80) logMAR for near VA. After the initial response categories were collapsed from five to three, content validity was further supported by good person and item fit parameters. The person separation index (PSI) was 0.85, which indicates that the IVI_C can assess QoL across children of several participation levels. The scale was shown to be unidimensional after principal components analysis (PCA) of the residuals (t-test; P = 0.48, P = 0.34). Significant differences in overall person measures between the vision-impaired and normally sighted groups substantiated the scale discriminant validity (ANOVA; F = 78.75; P < 0.0001). Guttman split-half correlations for temporal, mode (face-to-face and telephone), and interobserver administrations were 0.95, 0.90, and 0.86, respectively, supporting scale reliability.
CONCLUSIONS: The modified IVI_C is a unidimensional, reliable, and valid scale for assessing QoL of children with vision impairment. It provides a valid means of assessing the outcomes of interventions and needs in children with vision impairment.