The Italian version of the Glaucoma Symptom Scale Questionnaire: translation, validation, and reliability.

Purpose: To validate the Italian version of the Glaucoma Symptom Scale (GSS) Questionnaire and its symptoms and function subscales. Methods: This transversal validation study enrolled nonhospitalized patients with glaucoma, and a reference sample of patients without eye diseases. Eligible participants had to be cognitively able to respond to a health status interview. The Italian self-administered versions of the 25-item National Eye Institute-Visual Function Questionnaire and the GSS Questionnaire were administered to all participants. Reliability and validity of the Italian translation of the GSS Questionnaire were tested using standard statistical methods for questionnaire validation. Results: Ninety-seven patients were enrolled. Cronbach alpha coefficient ranged from 0.72 to 0.92 across subscales and eyes. Test-retest stability was > 85% for each subscale and eye. The control group of participants had better scale scores across all dimensions of vision-targeted health-related quality of life captured by the GSS Questionnaire (P<0.05) and there were good correlations between responses GSS Questionnaire subscales and analogous domains of the 25-item National Eye Institute-Visual Function Questionnaire. Conclusions: The Italian version of the GSS Questionnaire has good validity, discriminatory power, internal consistence and reliability, showing psychometric properties comparable with those of the English version, and can therefore be used in clinical research as a specific measure of vision-related quality of life in Italian-speaking patients with ocular hypertension or glaucoma.