Clusterin from human clinical tear samples: Positive correlation between tear concentration and Schirmer strip test results

Abstract

Results support the hypothesis that an optimal concentration of tear CLU is important for ocular surface health, and that this drops below the effective threshold in dry eye. Tear CLU measurement might identify patients that could benefit from supplementation. Information about concentration will aid development of therapeutic dosage parameters.

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“…A microcapillary glass tube (1-10 µl) placed in contact with the inferior lacrimal lake is the most commonly reported technique to collect tear fluid. This method directly samples tear fluid by capillary action and is extensively described in humans, 182,216,220,[226][227][228][229][230][231][232][233][234][235][236][237][238][239] dogs, 183,191,[240][241][242][243] rabbits, 188,237,238,241,244 mice, 245,246 and rats. 183,202,237,247 Other direct techniques (seldom reported) involve micropipettes, 248 polypropylene tubing, 183 or polytetrafluoroethylene tubing.…”

“…Another critical limitation of direct sampling is the low volume of tear fluid retrieved, generally ≤5 µl 182,183,220,226,227,230,[232][233][234]237,239,[244][245][246] -as such, the small sample collected may be grossly insufficient in some individuals, 182,242 may require excessive dilution that renders the target analyte undetectable, 243 and does not take into account possible losses (e.g., transfer and storage) or the need to repeat certain assays in duplicates.…”

“…41 cellulose filter paper and possess specific characteristics to promote tolerance (5-mm width × 35-mm length, 0.22-mm thick, 20-25 µm porosity, foldable extremity for ease of insertion). 249,257 In addition to their conventional use for aqueous tear assessment, Schirmer strips can retrieve tear fluid for bioanalytical purposes in humans, 182,216,219,220,228,231,258 dogs, 190,209,211,214,215,240,259 and small laboratory species. 244,260,261 For instance, Schirmer strips were used for indepth characterization of proteomics in human 173 and canine tears, 190 and can also successfully recover specific analytes such as cytokines, 200,258 clusterin, 182 and xenobiotics.…”

“…249,257 In addition to their conventional use for aqueous tear assessment, Schirmer strips can retrieve tear fluid for bioanalytical purposes in humans, 182,216,219,220,228,231,258 dogs, 190,209,211,214,215,240,259 and small laboratory species. 244,260,261 For instance, Schirmer strips were used for indepth characterization of proteomics in human 173 and canine tears, 190 and can also successfully recover specific analytes such as cytokines, 200,258 clusterin, 182 and xenobiotics. 211,[213][214][215]244,262 Absorbent sponges exist in different material types such as cellulose, 234,236,263,264 polyvinyl acetal, 209,214,228,236,244,264-266 polyester, 239,242,266 and polyrurethane.…”

“…Indirect tear collection is superior to direct capillary sampling in many aspects, namely: (i) Improved tolerance and acceptability by patients 182,231,266,267 ; (ii) Ease of use and operator safety, especially for Schirmer strips, allowing non-specialists to perform the procedure with minimal training 231,236,266 ; and (iii) Larger volume of tears collected in a shorter duration. 234,236,239,244 Absorbent materials collect tears but can also pick up cellular and extracellular "debris," an attribute considered beneficial by some as the sample obtained is more representative of the dynamic microenvironment at the ocular surface, 268 but also perceived as a limitation by others as the fluid retrieved is not "pure" tears.…”