Assessment of the Absorption Characteristics of Tear Production Tests Under Different Environmental Conditions

Abstract
Background: Aqueous deficiency dry eye is considered one of the main categories of dry eye syndrome. Many tech-niques have been developed to assess tear production and monitor tear film turnover. Methods such as Schirmer test, phenol red thread (PRT) test, and tear function index (TFI), have been widely used to diagnose aqueous deficient dry eye. All these tests are based on the principle of absorption of the tear from the lacrimal sac and then measuring the wetting length of the paper strip or cotton thread. The wetting length can be affected by environmental factors, particularly relative humidity, that could exert a strong effect on the absorption mechanism of the strips or threads used to measure tear production.
Aim of the Work: The aim of this study was to investigate the effect of changing room relative humidity on the absorption properties of phenol red thread (PRT) and Schirmer strips, and their accuracy of measuring tear film production.
Methods: Twenty healthy subjects (40 eyes) were recruited for this study. Tear film production was assessed using PRTs and Schirmer strips in two different environmental conditions. Two visits were required to conduct this study. One visit was used to measure tear production in a room without installing a humidifier. The other visit was used to measure tear film production after the room was humidified using portable air humidifiers.
Result: Mean tear production measurements in non-humidified room were 16.04-}4.09 and 16. 12±9. 10mm using PRTs and Schirmer strips respectively. At high humidity visit, mean measurements was 20-}8.03mm and 19.35-}8.35mm.
Conclusion: The physical properties of the examination strips and threads used for measuring tear quantity could be affected by environmental conditions. Eye care practitioners should be aware of the variation in tear production measure-ments that may result from external factors.