title: Evaluation of commonly used tear sampling methods and their relevance in subsequent biochemical analysis.
abstract: The human precorneal tear film is a special body fluid, since it is a complex mixture of proteins, lipids, small bioactive molecules, and their concentrations and relative distribution represent not only the metabolic state of the ocular surface but also the systemic and local homeostasis of the outer eye and the human body. This suggests that biochemical analysis of the precorneal tear film composition may provide a non-invasive tool for diagnosis and monitoring of disease progression or treatment efficacy in human medicine. However, collecting tears is demanding, and obtaining reproducible and unaltered samples is challenging because of the small sample volumes of tears. Several methods are available for tear collection as a preparatory step of precorneal tear film analysis, and the collection method used has to be assessed since it has a critical impact on the effectiveness of the assays and on the quality of the results. Each sampling method has advantages and disadvantages; therefore, it is not easy to choose the appropriate collecting method for tear collection. To overcome these limitations various methods have been recommended by different authors for special aspects of specific tests. The aim of our review was to evaluate tear sampling methods with regard to our ongoing biochemical analysis.
  
  *Contributed equally.
authors.affiliation: Department of Ophthalmology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
authors.forename: Aniko
authors.initials: A
authors.lastname: Rentka
authors.affiliation: Department of Biochemistry and Molecular Biology, Signaling and Apoptosis Research Group, Hungarian Academy of Sciences, Research Center of Molecular Medicine, University of Debrecen, Debrecen, Hungary.
authors.forename: Krisztina
authors.initials: K
authors.lastname: Koroskenyi
authors.affiliation: Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary.
authors.forename: Jolan
authors.initials: J
authors.lastname: Harsfalvi
authors.affiliation: Department of Rheumatology, Institute of Medicine, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Szekanecz
authors.affiliation: Department of Rheumatology, Institute of Medicine, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
authors.forename: Gabriella
authors.initials: G
authors.lastname: Szucs
authors.affiliation: Institute of Immunology, Rikshospitalet, Oslo University Hospital, Oslo, Norway.
authors.forename: Peter
authors.initials: P
authors.lastname: Szodoray
authors.affiliation: Department of Ophthalmology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
authors.forename: Adam
authors.initials: A
authors.lastname: Kemeny-Beke
mesh_terms: D019411:Clinical Laboratory Techniques / Q000379:methods*; D003933:Diagnosis; D006801:Humans; D013666:Tears / Q000378:metabolism*
keywords: Precorneal tear film; bioactive components; tear collection; tear diagnostics; tear sampling