Tear-based glucose monitoring: A non-invasive approach to diabetes control in resource-limited settings

Effective diabetes management may require continuous monitoring of blood glucose (BG) levels; however, conventional methods such as finger-prick testing and continuous glucose monitors (CGMs) remain invasive, costly, and often inaccessible, particularly in rural and remote Aboriginal and Torres Strait Islander (ATSI) communities. Recent advances in nanotechnology have enabled the development of nanosensor-embedded, near-field communication (NFC)-enabled smart contact lenses (SCLs) for non-invasive tear glucose (TG) monitoring. This systematic review, conducted in accordance with PRISMA guidelines, critically evaluated 12 peer-reviewed empirical studies encompassing clinical, cohort, and experimental designs involving both human and animal subjects. Study quality and risk of bias were assessed using NOS, ROBINS-I, and QUADAS-2 frameworks. Across the studies, TG levels demonstrated strong correlations with BG (R² = 0.87-0.998), mean absolute relative difference (MARD) values ranged between 12.5 % and 16.7 %, and over 95 % of readings fell within clinically acceptable error grid zones. A physiological lag of 5-10 min between TG and BG changes was consistently observed. Nanosensor-embedded SCLs showed stability, biocompatibility, and effective real-time wireless data transmission, with minimal impact on wearer comfort. Collectively, these findings support the feasibility of tear-based glucose monitoring as a non-invasive alternative to traditional approaches. However, validation in larger, more diverse populations and real-world conditions is required to establish clinical reliability. The potential application of these technologies in underserved ATSI communities underscores their promise for improving compliance, accessibility, and long-term health outcomes.