Psychometric evaluation of the Glaucoma Symptom Identifier.

OBJECTIVE: To evaluate the psychometric properties of the Glaucoma Symptom Identifier (GSI), a tool designed to assess multiple possible glaucoma symptoms and their impact on quality of life in clinical practice. We sought to address the need for better methods to assess visual function related to quality of life of glaucoma patients with a tool to show to both physicians and their patients that glaucoma is not an asymptomatic disease. The development process was to provide comprehensive assessment in 1 page of the impact of glaucoma on patients' quality of life by including an exhaustive list of unique and nonredundant items.
DESIGN: Cross-sectional online survey. PARTICIPANTS: Seven hundred and eighteen individuals with a self-reported diagnosis of glaucoma, who were at least 40 years of age.
METHODS: The impact of glaucoma was assessed by asking study participants the degree of difficulty they experience on a number of tasks. Item response theory was used to psychometrically evaluate the GSI. Scores on the GSI and the SF-12, a generic quality-of-life instrument, were compared. MAIN OUTCOME MEASURES: Items in the GSI were categorized in terms of their ability to capture glaucoma impact on quality of life across the population range of subjects from mild-to-severe glaucoma severity.
RESULTS: The GSI showed good reliability, and convergent and discriminant validity. Items in the GSI captured glaucoma impact on quality of life over an adequate range of disease severity. Potential improvements to the existing questionnaire were identified using item response theory modeling results and respondents' feedback on the survey.
CONCLUSIONS: Our findings suggest that the GSI is a psychometrically valid tool, adequate for glaucoma patients' self-administration within a clinician's routine practice to help both the patient and physician assess the patient's current and potential future symptoms of glaucoma.