Human tear fluid analysis for clinical applications: progress and prospects

ABSTRACT

Introduction: Human blood and saliva are increasingly under investigation for the detection of biomarkers for early diagnosis of non-communicable (e.g.cancers) and communicable diseases like 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.

Areas covered: This review deals with a comprehensive account of applications of tear analysis using different techniques, their comparison and overall progress achieved till now. The techniques used for tear fluid analysis are HPLC/UPLC/SDS-PAGE, CE, etc., together with ELISA, Mass Spectrometry, etc. But, with advances in instrumentation and data processing methods, it has become easy to couple the various separation methods with highly sensitive optical techniques for the analysis of body fluids.

Expert opinion: Tear analysis can provide valuable information about the health condition of the eyes since it contains several molecular constituents, and their relative concentrations may alter under abnormal conditions. Tear analysis has the advantage that it is totally non-invasive. This study recommends tear fluid as a reliable clinical sample to be probed by highly sensitive optical techniques to diagnose different health conditions, with special emphasis on eye diseases.

KEYWORDS:

• Biomarkers
• tears
• hyphenated techniques
• HPLC-LIF
• COVID-19

Article highlights

• Tears can be collected anywhere, any time; they provide a ready source for point of care (POC)/ bedside diagnostic tests for pathological conditions of ocular system including the body as a whole.

• The biomarkers in tears can be used as a successful alternative/complimentary technique to current methods, for diagnosis and early detection through the development of fast and inexpensive tear fluid assays.

• Optical spectroscopy (absorption, fluorescence, scattering), separation methods (HPLC/UPLC/SDS-PAGE) and mass spectroscopy, followed by hyphenated methods are the preferred methods for tear fluid analysis.

• Ultra-sensitive high-performance liquid chromatography coupled with laser induced fluorescence (HPLC-LIF) setup can be utilized for the detection of protein markers of the order of sub-femto-moles using small (microgram) quantities of tear fluids.

Acknowledgments

Authors are thankful to VGST (GRD No. 459), Govt. of Karnataka, for the sanction of a grant to establish an HPLC facility under the scheme Centre of Excellence in Science, Engineering and Medicine (CESEM) and DST-FIST for supporting the department to setup a nano bioimaging facility. Ms. Sphurti Adigal is thankful to Manipal Academy of Higher Education for the Dr. TMA Pai Ph.D. Scholarship.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This paper was not funded.