Development and Validation of a Preference-Based Glaucoma Utility Instrument Using Discrete Choice Experiment

IMPORTANCE: A glaucoma-specific instrument for estimating utilities across the spectrum of glaucoma severity is currently lacking, hindering the assessment of the cost-effectiveness of glaucoma treatments. OBJECTIVE: To develop and validate the preference-based Glaucoma Utility Instrument (Glau-U) and to ascertain the association between Glau-U utilities and severity of glaucoma and vision impairment. DESIGN, SETTING, AND PARTICIPANTS: This cross-sectional study was conducted in 2 stages at the Singapore National Eye Centre glaucoma clinics. Stage 1 focused on the identification and pretesting of the Glau-U attributes and was carried out between June 2009 and May 2016. Stage 2 involved the development and administration of the discrete choice experiment (DCE) survey and tasks and was conducted between May 7, 2018, and December 11, 2019. Stage 2 participants were English- or Mandarin-speaking Singaporean citizens or permanent residents of Chinese, Malay, or Indian ethnicity who were 40 years or older and had a clinical diagnosis of glaucoma in at least 1 eye. EXPOSURES: Glau-U comprised 6 quality-of-life attributes: activities of daily living, lighting and glare, movement, eye discomfort, other effects of glaucoma, and social and emotional effects. The descriptions or response options for these attributes were no difficulty or never, some difficulty or sometimes, or severe difficulty or often. MAIN OUTCOMES AND MEASURES: Utility weights for Glau-U were developed using a DCE questionnaire, which was interviewer administered to participants. Mixed logit regression determined utility weights for each health state. Glau-U utility weights across better- or worse-eye glaucoma and vision impairment severity were calculated using 1-way analysis of variance. Correlations between Glau-U utilities and better- or worse-eye visual fields and EuroQol 5-Dimension utilities were ascertained to assess convergent and divergent validity. RESULTS: Of the 304 participants (mean [SD] age, 68.3 [8.7] years; 182 men [59.9%]), 281 (92.4%) had no vision impairment in the better eye, 13 (4.3%) had mild impairment, and 10 (3.3%) had moderate to severe vision impairment. Mean (SD) Glau-U utilities decreased as better-eye glaucoma severity increased (none: 0.73 [0.21]; mild: 0.66 [0.21]; moderate: 0.66 [0.20]; severe: 0.60 [0.28]; and advanced or end-stage: 0.22 [0.38]; P