Association of Comprehensive Geriatric Assessment with Knowledge- and Technique-Related Eye Drop Adherence Problems in Glaucoma Assessed Using the Shimane University Glaucoma Eye Drop Adherence Questionnaire

Background/Objectives: Glaucoma medication adherence is influenced by multiple factors, including treatment-related knowledge, eye drop instillation technique, cognitive function, and systemic health status. However, the relationships between comprehensive geriatric assessment (CGA) results and specific adherence-related problems remain poorly understood. This study investigated the associations between CGA results and glaucoma eye drop adherence-related problems using the newly developed Shimane University Glaucoma Eye Drop Adherence Questionnaire (SU-GAQ). Methods: This retrospective study included 187 consecutive glaucoma patients who underwent CGA and completed the SU-GAQ at Shimane University Hospital. The SU-GAQ consists of Knowledge (Q1–Q5) and Technique (Q6–Q15) domains. CGA included the Mini-Cog, G8, and Age-Adjusted Charlson Comorbidity Index (ACCI). Associations between questionnaire responses and CGA results were evaluated using Spearman’s rank correlation and generalized regression analyses. Exploratory factor analysis (EFA) based on tetrachoric correlations was performed to evaluate the questionnaire structure. Results: Lower Mini-Cog scores were significantly associated with higher Knowledge-domain scores (ρ = −0.27, p = 0.0002) and higher overall questionnaire scores (ρ = −0.23, p = 0.002). In multivariate analysis, Mini-Cog remained independently associated with the Knowledge domain (estimate = −0.31, p < 0.0001) and total score (estimate = −0.44, p = 0.002). Higher ACCI scores were associated with higher Technique-domain scores (ρ = 0.19, p = 0.009) and remained significant in multivariate analysis (estimate = 0.16, p = 0.02). G8 scores were not significantly associated with questionnaire outcomes. EFA identified a two-factor structure corresponding to the predefined Knowledge and Technique domains, accounting for 71.2% of the total variance. Conclusions: Lower cognitive function was primarily associated with knowledge-related barriers to glaucoma medication adherence, whereas greater comorbidity burden was associated with technical difficulties in eye drop instillation. The SU-GAQ demonstrated a clinically meaningful two-domain structure and may facilitate identification of specific adherence-related barriers in glaucoma patients.