Human Tear Fluid Analysis for Clinical Applications: Progress and Prospects.

Human blood and saliva are increasingly under investigation for the detection of biomarkers for early diagnosis of non-communicable diseases like cancers, diabetes, cardiovascular diseases, etc. as well as communicable diseases like coronavirus disease-2019 (COVID-19). Exploring the potential application of human tears, an easily accessible body fluid, for the diagnosis of various diseases is the need of the hour. A thin layer of tears covers the ocular surface, which acts as a mechanical and antimicrobial obstacle and maintains the optical refractive property. Variations in the composition of tears and its quantities in eyes can be reflection of the health status of eyes. In this respect, tear analysis is getting extreme attention from the ophthalmology community. This review deals with a comprehensive account of applications of tear analysis using different techniques, their comparison and overall progress achieved till now.Areas covered:This report presents an assessment of the analysis of tears like that of other body fluids, for clinical applications both for ophthalmic and other conditions like different cancers, diabetes, coronary diseases etc. At present the techniques used for tear fluid analysis are separation methods like HPLC/UPLC/SDS-PAGE, CE etc., together with complex detection techniques like ELISA, MS etc. But, advances in instrumentation and data processing methods like PCA, ANN, it has become easy to couple the various separation methods with highly sensitive optical techniques for the analysis of complex systems like many body fluids: blood, Saliva, Tears etc.Expert opinion:Tear analysis can provide valuable information about the health condition of eyes since it contains several organic and inorganic constituents, and their relative concentrations may alter under abnormal conditions. Tear analysis has the advantage that it is totally non-invasive, easily accessible and is thus acceptable to all age groups and genders, who otherwise may be reluctant to undergo personally invasive diagnostic methods. Our report strongly recommends tear fluid as clinical sample probed by highly sensitive optical techniques to evaluate different health conditions, with special emphasis on diagnosis of eye diseases (e.g., dry eye syndrome).