18 However, phenol red thread allows similar collection of tear fluid with a significantly smaller contact area, allowing lower tear sampling volume and minimal irritation and reflex impact on the ocular surface for subsequent chemical analysis. 14, 16, 17 Common absorbent material for tear collection include Schirmer filter paper strip, phenol red thread, and other cellulose ophthalmic sponges, with the Schirmer strip being used most often for tear analysis. 22, 23 Alternatively, the sorbent approach allows the collection of low-volume samples via capillary action and has been used previously with patients with dry eye 24 and in unanesthetized animal models. 18, 20, 21 In addition, this approach requires extreme care and would likely require anesthesia with animal models, which has been reported to have significant impacts on the ocular surface. When tears are limited, a washout of the tear film can be used, which facilitates collection but introduces an unknown dilution factor and impacts tear chemical analysis. 18, 19 The relatively large sampling volume associated with the capillary approach makes it less suitable for collection from rodents and aqueous tear-deficient patients. To address this issue, we explored the impacts of phenol red thread fiber-based sample collection as well as processing on tear fluid chemical content using capillary electrophoresis with light-emitting diode-induced fluorescence detection.Ĭollection of tear fluid from humans and animal models for chemical analysis is typically performed either directly into a glass microcapillary tube or via an absorbent material. It is crucial to define the impacts of collection and processing methods on tear analysis to standardize results drawn from different studies.
6 – 17 Yet the impact of these analytical methods on the chemical composition of tear fluid is largely unexplored. 4, 5 The most commonly used methods for noninvasive tear analysis in both clinical and research settings from humans and animal models involve collection and processing via absorbent material, such as thread and filter paper. 3 This nature makes tear fluid analysis suitable for monitoring ocular surface health and disease. Tear film chemical composition, which includes electrolytes, proteins, lipids, and small molecule metabolites, is reflective of corneal biochemistry and physiology 1, 2 and can ultimately be indicative of both ocular as well as systemic pathology.
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