Abstract
BACKGROUND: Despite the availability of various methods for assessing medication adherence, limited guidance exists regarding the most appropriate tool, particularly for measuring glaucoma medication adherence. OBJECTIVE: To achieve expert consensus on the appropriate tool for measuring glaucoma medication adherence using the Delphi technique. METHODS: A two-round Delphi study was conducted with a panel of experts from diverse fields, assessing three validated adherence measurement tools. Consensus was determined using Kendall's Coefficient of Concordance. The extent of agreement and inter-rater reliability were evaluated using the scale-level content validity index (SCVI) and intraclass correlation coefficients (ICC), analysed in SPSS version 25. RESULTS: Sixteen experts (mean age 53.8 ± 7.1 years; mean professional experience: 21.9 ± 6.8 years) participated. Consensus levels of 81.0% and 89.0% were achieved in the first and second rounds, respectively. Agreement on non-adherence characteristics was high (SCVI and ICC values > 0.75). The most appropriate tool for measuring non-adherence to glaucoma medication was the Glaucoma Treatment Compliance Assessment Tool-Short form (GTCAT-S) with an SCVI of 0.91 and ICC of 0.94 (95% CI: 0.78-0.99; p = 0.001). CONCLUSIONS: The GTCAT-S was identified as the most suitable tool for measuring non-adherence to glaucoma medication. It demonstrated a high SCVI and excellent inter-rater reliability, indicating strong consensus among experts and robust measurement consistency.