Tear fluid collection methods: Review of current techniques

Abstract

Tear fluid, composed of lipid, aqueous, and mucin layers, contains electrolytes, water, proteins, peptides, and glycoproteins. Its components may serve as diagnostic indicators of local and systemic diseases. The aim of the study was to conduct literature review in order to identify the current methods of tear collection. The most commonly used method which was relatively easy to perform and allowed to obtain sufficient tear volume for further chemical and physical analysis was selected through PubMed database search for the following keywords: tear sampling, human tears, chemical analysis of tears, physical tear analysis, animal tear sampling. Final criteria of articles selection were: human tears, tear sample collection, chemical and physical analysis of tears. Time of publication of the articles not older than 1995. The analysis of 70 articles revealed that the most common tear fluid collection methods are Schirmer tear strips and capillary tubes. Thus, we recommend the use of Schirmer strips and microcapillary tubes as the cheapest and easiest methods for sampling of tear fluid for further chemical analysis.

Evaluation of vascular endothelial growth factor (VEGF) level in the tears and serum of age-related macular degeneration patients

“…Schirmer strip was used for tear fluid collection. The Schirmer strip collection method is a simple procedure, cheap, well tolerated, and relatively painless, with minimal to no discomfort; hence, it is considered superior to the other tear fluid collection methods, including microcapillary tubes, surgical sponges, cellulose acetate filters, rods, spatulas, glass rods, and microsponges 31 – 35 . The major drawback of Schirmer strips is that the collected volume of tears is not readily available, and there is a need for post-processing procedure, which may alter the final protein concentration 33 , 35 .…”

“…It not only reflects the health status of the ocular surface, but it also enables monitoring and understanding of the clinical aspects of many intraocular diseases 13 , 21 , 28 – 30 . The tear film is readily accessible, and collection is easily performed using various methods, such as microcapillary tubes, Schirmer strip, or surgical sponges 31 . There are no prior studies evaluating VEGF levels in the tear fluid of AMD patients.…”

Antimicrobial Tear Lipids in the Ocular Surface Defense

“…The reliable techniques for identifying lipids have included mass spectrometry-based techniques such as high performance liquid chromatography-mass spectrometry (HPLC-MS), LC-MS with MS fragmentation, and electrospray ionization-mass spectrometry (ESI-MS) ( Butovich et al., 2007 ; Chen et al., 2010 ; Lam et al., 2014 ; Chen et al., 2019 ), while nuclear magnetic resonance is deemed useful for quantification of lipids ( Butovich, 2013 ; Willcox et al., 2017 ). Tear collection techniques also affect the lipid profiles and indicate that basal tears collection with capillary tubes is a preferred method ( Lam et al., 2014 ; Rentka et al., 2017 ; Pieczyński et al., 2021 ). The amounts of various lipid species in tears vary in different studies due to various analytical techniques and collection methods used, and are reviewed elsewhere ( Pucker and Nichols, 2012 ; Butovich, 2013 ; Pucker and Haworth, 2015 ; Willcox et al., 2017 ).…”

Proteomic Analysis of Tears and Conjunctival Cells Collected with Schirmer Strips Using timsTOF Pro: Preanalytical Considerations

“…Despite its small volume, TF offers several advantages for biochemical analysis, biomarker discovery, and development of new drugs [5][6][7][8][9]. TF can be collected with various instruments such as microcapillary tubes, absorbent cellulose acetate filters, polyester wicks, and Schirmer strips (ScS) [10,11], the latter of which is used by clinicians to perform the Schirmer's tear test (STT). The STT is a standard ophthalmologic test that measures tear production based on the wetted length of the strip.…”