9 in this case biological molecules associated with the disease in question. Scientists are exploring clinical applications for various diseases, from eye diseases like dry eye disease and allergic conjunctivitis, to neurological diseases like Alzheimer’s disease. For instance, in a subtype of dry eye disease caused by a deficiency in aqueous tear, inflammatory cytokines are synthesized and released to promote inflammation. Multiple studies reported that IL-6, IL-8, and IL-17 are three inflammatory cytokines that could potentially be the biomarkers for the diagnosis of aqueous-deficient dry eye disease [8]. Tear test, if successfully developed, could also help with the diagnosis of another eye disease, allergic conjunctivitis (AC). Type IV AC is associated with prolonged exposure to allergens, but it is often mistaken for seasonal type I AC in clinical practice. A quick test to quantify the amount of IgE in tear fluid could reliably differentiate the two conditions because low IgE levels are found to be indicative of type IV AC. The test will enable physicians to administer appropriate medication to the patients [9]. Non-invasive tear tests could also become an easy screening method for various neurological diseases because the elevated level of biomarkers in cerebrospinal fluid is also observed in tears in some cases. For example, TNF-alpha and alpha 1-antichymotrypsin are two such biomarkers for Parkinson’s disease and multiple sclerosis, respectively [10]. Scientists are also making efforts to identify reliable biomarkers for Alzheimer’s disease. If tearbased screening methods can be developed and commercialized eventually, we will be able to promote population screening in the community. Early diagnosis and treatment can improve the quality of life for both the patients and their caregivers [11]. As for tear-based biodevices, a recent study suggested the possibility for diabetic patients to continuously monitor their tear glucose level with a smart contact lens [12]. The previous challenge of using tear glucose level as an alternative indicator for blood glucose was that single measurement using conventional tear collection methods, such as filter paper strip and capillary tube, always undesirably induce the generation of reflex tears, which will interfere with the results. By embedding an antenna, a glucose sensor and an NFC chip in the soft contact lens, the research team could continuously monitor the glucose level in basal tears, with the ability to transfer real-time data to a mobile device. While tears may contain a wide array of biomarkers that can reveal our health status, there is still a long way to go before relevant technologies can reach the clinic. With extensive research efforts working on the identification of biomarkers and the development of smarter biodevices, tears can one day become a powerful indicator of our health. The Shape of Tears One way to artistically study tears is to observe them under a microscope – by observing the airdried salt crystals or the tear fluid compressed between a microscopic slide and a coverslip [13]. A photographer, Rose-Lynn Fisher, created a project called “The Topography of Tears,” in which she captured the diverse morphology of tears shed by herself and her friends on various occasions. More about the project:
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