![]() There is no single conclusive representation for the exact structure of tear fluid. ![]() The primary functions of tear film include the following: (i) lubricate and lessen the friction between the eye surface and the eyelids during blinking, and to moisten the ocular surface between the palpebral and bulbar conjunctiva, (ii) provide oxygen and electrolytes to the cornea that are essential for corneal metabolism, (iii) increase the refractive power of the eye because a healthy tear film might enhance the optical quality, and (iv) protect the eye from environment debris and bacterial infection with a physical flush and antibacterial constituents such as lysozyme and secretory immunoglobin A (sIgA). Tear film serves as the first barrier between the external environment and the eye to play a crucial role to protect and maintain the health of the ocular surface. Normally, the amount of tear fluid is 5–10 ml with a secretion rate of ~ 1.2 μl per minute and a turnover rate of ~ 16% per minute. Generally, reflex tear secretion is triggered by activation of the corneal nerves due to an irritating stimulus. Under normal conditions, reflex tears as well as tear flow derive from the main lacrimal glands, whereas basal tears might be triggered from accessary lacrimal glands. In addition, an ultrafiltrate of blood contributes to the composition of tear fluid. The intricate secretion and structure of tear film derive from its various secretory units, including lacrimal glands, meibomian glands, accessory lacrimal glands, sebaceous glands of Zeis and Moll, and corneal and conjunctival cells. Tears serve as a crucial optical smooth surface to refract light from air onto the retina, and are an important and complex body fluid. Tears, also known as tear fluid or tear film, are the outermost thin liquid layer that covers the ocular surface epithelial cells to form an anterior meniscus component at the eyelid margins. In the context of 3P medicine, tear fluid analytical pathways are considered to predict disease development, to target preventive measures, and to create treatment algorithms tailored to individual patient profiles. Consequently, we proposed the overall strategies based on the tear fluid biomarkers application for 3P medicine practice. Corresponding analytical approaches such as sample pre-processing, differential proteomics, electrophoretic techniques, high-performance liquid chromatography (HPLC), enzyme-linked immuno-sorbent assay (ELISA), microarrays, and mass spectrometry (MS) methodology are detailed. In this review, protein profiles in tear fluid are highlighted and corresponding biomarkers are exemplified for several relevant pathologies, including dry eye disease, diabetic retinopathy, cancers, and neurological disorders. One prominent example is the Sicca syndrome linked to a cascade of severe complications that include dry eye, neurologic, and oncologic diseases. ![]() ![]() The well-justified principle of a “sick eye in a sick body” makes comprehensive tear fluid biomarker profiling highly relevant not only for diagnostics of eye pathologies but also for prediction, prognosis, and treatment monitoring of systemic diseases. These requirements are clearly fulfilled by tear fluid, which represents a precious source of biomarker panels. Furthermore, any diagnostic approach preferentially should be noninvasive to increase availability of the biomaterial, and to decrease risks of potential complications as well as concomitant costs. The source of biomarkers is crucial for specificity and reliability of diagnostic tests and treatment targets. To this end, specific biomarker panels are instrumental for a cost-effective predictive approach of individualized prevention and treatments tailored to the person. The paradigm change from reactive to predictive, preventive, and personalized medicine (3PM/PPPM) has been declared as an essential transformation of the overall healthcare approach to benefit the patient and society at large. Over the last two decades, a large number of non-communicable/chronic disorders reached an epidemic level on a global scale such as diabetes mellitus type 2, cardio-vascular disease, several types of malignancies, neurological and eye pathologies-all exerted system’s enormous socio-economic burden to primary, secondary, and tertiary healthcare. ![]()
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