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      Tear Osmolarity in the Diagnosis of Systemic Dehydration and Dry Eye Disease

      review-article
      1 , * , 2
      Diagnostics
      MDPI
      basal tear osmolarity, dehydration, dry eye, plasma osmolality, tonicity, hyperosmolar

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          Abstract

          Systemic dehydration due to inadequate water intake or excessive water loss, is common in the elderly and results in a high morbidity and significant mortality. Diagnosis is often overlooked and there is a need for a simple, bedside diagnostic test in at-risk populations. Body hydration is highly regulated with plasma osmolality (pOsm) being tightly controlled over a wide range of physiological conditions. By contrast, normal tear osmolarity (tOsm) is more variable since the tear film is exposed to evaporation from the open eye. While plasma hyperosmolality is a diagnostic feature of systemic dehydration, tear hyperosmolality, with other clinical features, is diagnostic of dry eye. Studies in young adults subjected to exercise and water-deprivation, have shown that tOsm may provide an index of pOsm, with the inference that it may provide a simple measure to diagnose systemic dehydration. However, since the prevalence of both dry eye and systemic dehydration increases with age, the finding of a raised tOsm in the elderly could imply the presence of either condition. This diagnostic difficulty can be overcome by measuring tear osmolality after a period of evaporative suppression (e.g., a 45 min period of lid closure) which drives tOsm osmolality down to a basal level, close to that of the pOsm. The arguments supporting the use of this basal tear osmolarity (BTO) in the diagnosis of systemic dehydration are reviewed here. Further studies are needed to confirm that the BTO can act as a surrogate for pOsm in both normally hydrated subjects and in patients with systemic dehydration and to determine the minimum period of lid closure required for a simple, “point-of-care” test.

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          TFOS DEWS II Epidemiology Report

          The subcommittee reviewed the prevalence, incidence, risk factors, natural history, morbidity and questionnaires reported in epidemiological studies of dry eye disease (DED). A meta-analysis of published prevalence data estimated the impact of age and sex. Global mapping of prevalence was undertaken. The prevalence of DED ranged from 5 to 50%. The prevalence of signs was higher and more variable than symptoms. There were limited prevalence studies in youth and in populations south of the equator. The meta-analysis confirmed that prevalence increases with age, however signs showed a greater increase per decade than symptoms. Women have a higher prevalence of DED than men, although differences become significant only with age. Risk factors were categorized as modifiable/non-modifiable, and as consistent, probable or inconclusive. Asian ethnicity was a mostly consistent risk factor. The economic burden and impact of DED on vision, quality of life, work productivity, psychological and physical impact of pain, are considerable, particularly costs due to reduced work productivity. Questionnaires used to evaluate DED vary in their utility. Future research should establish the prevalence of disease of varying severity, the incidence in different populations and potential risk factors such as youth and digital device usage. Geospatial mapping might elucidate the impact of climate, environment and socioeconomic factors. Given the limited study of the natural history of treated and untreated DED, this remains an important area for future research.
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            WHO estimates of the causes of death in children.

            Child survival efforts can be effective only if they are based on accurate information about causes of deaths. Here, we report on a 4-year effort by WHO to improve the accuracy of this information. WHO established the external Child Health Epidemiology Reference Group (CHERG) in 2001 to develop estimates of the proportion of deaths in children younger than age 5 years attributable to pneumonia, diarrhoea, malaria, measles, and the major causes of death in the first 28 days of life. Various methods, including single-cause and multi-cause proportionate mortality models, were used. The role of undernutrition as an underlying cause of death was estimated in collaboration with CHERG. In 2000-03, six causes accounted for 73% of the 10.6 million yearly deaths in children younger than age 5 years: pneumonia (19%), diarrhoea (18%), malaria (8%), neonatal pneumonia or sepsis (10%), preterm delivery (10%), and asphyxia at birth (8%). The four communicable disease categories account for more than half (54%) of all child deaths. The greatest communicable disease killers are similar in all WHO regions with the exception of malaria; 94% of global deaths attributable to this disease occur in the Africa region. Undernutrition is an underlying cause of 53% of all deaths in children younger than age 5 years. Achievement of the millennium development goal of reducing child mortality by two-thirds from the 1990 rate will depend on renewed efforts to prevent and control pneumonia, diarrhoea, and undernutrition in all WHO regions, and malaria in the Africa region. In all regions, deaths in the neonatal period, primarily due to preterm delivery, sepsis or pneumonia, and birth asphyxia should also be addressed. These estimates of the causes of child deaths should be used to guide public-health policies and programmes.
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              TFOS DEWS II Diagnostic Methodology report

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                Author and article information

                Contributors
                Role: Academic Editor
                Journal
                Diagnostics (Basel)
                Diagnostics (Basel)
                diagnostics
                Diagnostics
                MDPI
                2075-4418
                25 February 2021
                March 2021
                : 11
                : 3
                : 387
                Affiliations
                [1 ]Nuffield Department of Clinical Neurosciences and Nuffield Laboratory of Ophthalmology, University of Oxford, Oxford OX2 6HZ, UK
                [2 ]Ophthalmology Research, Hinchingbrooke Hospital, North West Anglia Trust, Huntingdon PE29 6NT, UK; catherine.willshire@ 123456nhs.net
                Author notes
                Author information
                https://orcid.org/0000-0003-0349-7465
                Article
                diagnostics-11-00387
                10.3390/diagnostics11030387
                7996182
                33668748
                4a8164f3-5e8d-43ac-8dc2-102678413dbe
                © 2021 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 10 January 2021
                : 18 February 2021
                Categories
                Review

                basal tear osmolarity,dehydration,dry eye,plasma osmolality,tonicity,hyperosmolar

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