Traditional chinese medicine monomers in dry eye disease: Pharmacological mechanisms, tear film stability, and translational challenges

Introduction Dry eye disease (DED) is characterized by persistent disruption of tear film homeostasis, and durable restoration remains challenging. Traditional Chinese medicine (TCM) monomers are chemically defined bioactive compounds that may modulate multiple pathogenic processes. This review evaluates their pharmacological actions and translational limitations, using tear film stability as the central functional framework. Methods PubMed/MEDLINE, Web of Science Core Collection, and Scopus were searched from inception to July 28, 2026 for DED and tear-film phenotypes, TCM monomers, mechanisms, and functional outcomes. Direct evidence was restricted to single chemically characterized compounds. Extracts, polysaccharides, total saponin or flavonoid fractions, and multicomponent preparations were not considered direct monomer evidence. In vitro, animal, and clinical findings were distinguished; non-ocular evidence was used only to generate hypotheses. Results Preclinical studies suggest that selected TCM monomers may attenuate inflammation, oxidative stress and ferroptosis, preserve epithelial barrier integrity, and support mucin-related function. Models showed improvements in tear breakup time, tear secretion, corneal staining, and epithelial protection. However, direct evidence for regulation of meibomian gland lipid metabolism by individual monomers remains sparse and largely indirect, and human clinical evidence is limited. Safety evidence is mainly indirect; ocular pharmacokinetics and long-term topical safety remain insufficiently characterized. Discussion TCM monomers may provide a multi-pathway approach to preserving ocular surface wettability, epithelial integrity, and tear film continuity. Nevertheless, proposed effects on meibomian lipid metabolism and population-specific safety signals should be regarded as hypothesis-generating until they are confirmed in standardized monomer-level models and clinical studies. Translation will require standardized tear-film endpoints, pathway-specific validation, rigorous quality control, ocular pharmacokinetic characterization, long-term safety assessment, and biocompatible ophthalmic formulations.