Tear fluid collection methods: Review of current techniques

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.

How to measure retinal microperfusion in patients with arterial hypertension

PURPOSE

Assessment and monitoring of changes in microcirculatory perfusion, perfusion dynamic, vessel structure and oxygenation is crucial in management of arterial hypertension. Constant search for non-invasive methods has led the clinical focus towards the vasculature of the retina, which offers a large opportunity to detect the early phase of the functional and structural changes in the arterial hypertension and can reflect changes in brain vasculature. We review all the available methods of retinal microcirculation measurements including angiography, oximetry, retinal vasculature assessment software, Optical Coherence Tomography Angiography, Adaptive Optics and Scanning Laser Doppler Flowmetry and their application in clinical research.

MATERIALS AND METHODS

To further analyse the applicability of described methods in hypertension research we performed a systematic search of the PubMed electronic database (April 2020). In our analysis, we included 111 articles in which at least one of described methods was used for assessment of microcirculation of the retina in hypertensive individuals.

RESULTS

Up to this point, the methods most commonly published in studies of retinal microcirculation in arterial hypertension were Scanning Laser Doppler Flowmetry followed shortly by Optical Coherence Tomography Angiography and retinal vasculature assessment software.

CONCLUSIONS

While none of described methods enables the simultaneous measurement of all microcirculatory parameters, certain techniques are widely used in arterial hypertension research, while others gain popularity in screening.