Tear-film evaporation flux and its relationship to tear properties in symptomatic and asymptomatic soft-contact-lens wearers.

PURPOSE: With soft-contact-lens wear, evaporation of the pre-lens tear film affects the osmolarity of the post-lens tear film and this can introduce a hyperosmotic environment at the corneal epithelium, leading to discomfort. The purposes of the study are to ascertain whether there are differences in evaporation flux (i.e., the evaporation rate per unit area) between symptomatic and asymptomatic soft-contact-lens wearers, to assess the repeatability of a flow evaporimeter, and to assess the relationship between evaporation fluxes, tear properties, and environmental conditions. METHODS: Closed-chamber evaporimeters commonly used in ocular-surface research do not control relative humidity and airflow, and, therefore, misestimate the actual tear-evaporation flux. A recently developed flow evaporimeter overcomes these limitations and was used to measure accurate in-vivo tear-evaporation fluxes with and without soft-contact-lens wear for symptomatic and asymptomatic habitual contact-lens wearers. Concomitantly, lipid-layer thickness, ocular-surface-temperature decline rate (i.e., °C/s), non-invasive tear break-up time, tear-meniscus height, Schirmer tear test, and environmental conditions were measured in a 5 visit study. RESULTS: Twenty-one symptomatic and 21 asymptomatic soft-contact-lens wearers completed the study. A thicker lipid layer was associated with slower evaporation flux (p < 0.001); higher evaporation flux was associated with faster tear breakup irrespective of lens wear (p = 0.006). Higher evaporation flux was also associated with faster ocular-surface-temperature decline rate (p < 0.001). Symptomatic lens wearers exhibited higher evaporation flux than did asymptomatic lens wearers, however, the results did not reach statistical significance (p = 0.053). Evaporation flux with lens wear was higher than without lens wear but was also not statistically significant (p = 0.110). CONCLUSIONS: The repeatability of the Berkeley flow evaporimeter, associations between tear characteristics and evaporation flux, sample-size estimates, and near statistical significance in tear-evaporation flux between symptomatic and asymptomatic lens wearers all suggest that with sufficient sample sizes, the flow evaporimeter is a viable research tool to understand soft-contact-lens wear comfort.

Measurements of Tear Evaporation Rate in Subjects with Refractive Errors Using a Portable Evaporimeter.

Dry eye symptoms are associated with refractive errors. We aimed to measure the tear evaporation rate (TER) in subjects with refractive errors (RE) using a portable evaporimeter. This nonrandomized, case-control, and observational study included 75 subjects, including 25 subjects aged 18-38 years (28.8 ± 6.8 years) with myopia (-0.75 to -3.75 D) and 25 subjects aged 18-39 years (27.7 ± 5.5 years) with hyperopia (+0.50 to +3.75 D). In addition, a control group of 25 subjects with emmetropic eyes aged 20-30 years (23.6 ± 2.6 years) was recruited. The ocular surface disease index (OSDI) was completed, followed by the TER measurements using a portable evaporimeter. The OSDI score and TER measurements showed dry eye symptoms in 36% and 48% of myopic subjects, respectively. For hyperopic participants, dry eye was observed in 24% and 56% of the subjects based on the OSDI and TER scores, respectively. Significant differences (Mann-Whitney U test; p < 0.001) were found among the OSDI and TER scores recorded within the study (myopic and hyperopic subjects) and control groups. Significant strong positive correlations were detected between the OSDI and TER scores in both myopic (p = 0.004; r = 0.559) and hyperopic (p = 0.001; r = 0.619) subjects. The TER scores were significantly higher in subjects with RE (myopic and hyperopic) as compared with individuals with normal eyes.

Reliability of methods to determine cutaneous evaporative water loss rate in furred and fleeced mammals.

We used a high-precision weighing system and flow-through respirometry to quantify cutaneous evaporative water loss rates in woolly sheep (wool thickness, ca. 6.5 cm) and haired goats (coat thickness, ca. 2.5 cm), while simultaneously recording parallel data obtained from (1) a flow-through ventilated capsule, (2) a closed hand-held electronic evaporimeter chamber, and (3) a closed colorimetric paper disc chamber. In comparison to the weighing system and respirometry, used here as a "gold standard" measure of cutaneous evaporative water loss rate, we found relatively good agreement with data obtained from the flow-through ventilated capsules. However, we found poor agreement with data obtained from the closed electronic evaporimeter chambers (underestimated by 60%, on average) and the closed colorimetric paper disc chambers (overestimated by 52%, on average). This deviation was likely associated with a requirement for shaved skin in the closed chamber methods. Our results therefore cast doubt on the validity of the closed chamber methods for measurement of cutaneous evaporative water loss rates in furred and fleeced mammals, and instead show that more accurate values can be obtained using flow-through ventilated capsules.

Unbearable transepidermal water loss (TEWL) experimental variability: why?

Despite the wide breadth of research, much disparity exists in transepidermal water loss (TEWL) research data-possibly due to uncontrolled experimental variables. We determined whether such experimental variables significantly impact TEWL studies and cause this disparity. An initial literature search regarding TEWL was performed to determine potential confounding variables. A subsequent search procured relevant and representative studies investigating the impact of these variables on TEWL. Variables, such as age, anatomic site, and temperature, impact TEWL and should be controlled for in TEWL studies. Other variables, such as smoking and menstrual cycle, have inconclusive results or do not provide sufficient data breadth to make a conclusion regarding its effect, if such an effect exists, on TEWL metrics. Therefore, these variables require further research to determine their potential impact on TEWL. Matching for as many experimental variables as possible may reduce the disparity in TEWL data/conclusions.

Performance of a double-slope solar still for the concentration of lithium rich brines with concomitant fresh water recovery.

Lithium recovery from brines has become a hot topic. The current evaporitic technology is slow, and serious environmental concern has been raised regarding the large volumes of water used, relating both to brine concentration through evaporation, and intensive pumping of fresh water needed in the fine chemical processing to produce high purity lithium carbonate. In this work, an experimental and theoretical analysis of brine desalination using a double-slope Solar Still was carried out. The Solar Still was installed right next to an existing lithium mining facility in northwest Argentina, and was tested with native high salinity lithium rich brine for a continuous year under the typical weather conditions of lithium deposits: high altitude, large thermal amplitude between day and night, strong winds, and high solar radiation. The performance of the solar still as an evaporator was compared with that of a PAN evaporimeter class A, and correlated to experimentally determined weather parameters. While the performance of the Solar Still for brine concentration was below that of open air evaporation, the Solar Still allowed for the production of an average of 2 L day-1 m-2 of distilled water, in marked contrast with current practice. Numerical simulations allowed us to quantify heat exchanges in both the Solar Still and the open air system.

A refined method to evaluate diapers for effectiveness in reducing skin hydration using the adult forearm.

BACKGROUND/AIMS: Excessive skin hydration resulting from wet undergarments is a major cause of diaper rash in children and contributes to severe dermatitis in incontinent adults. Advancements in absorbent technology have led to diapers and incontinent garments that not only absorb urine, but also transfer it to different regions, and lock it away from the skin. The purpose of the present study was to develop a reliable method to assess the effectiveness of absorbent articles in mitigating skin hydration. METHODS: Disposable diapers with different absorbent structures were wrapped around the forearms of adult volunteers, loaded with urine substitute, and held in place for 1 h. Hydration of the volar region was measured by evaporimetry and compared with that of skin in the diaper region of children who had worn control loaded diapers in the usual way. The amount of fluid retained in various diaper layers and in the superabsorbent polymer core was measured. CONCLUSIONS: Evaporative water loss measurement on adult forearms was shown to be a reliable test for comparing the effectiveness of absorbent articles in preventing excessive skin hydration provided that 1) the complete garment was used and 2) fluid was loaded in a manner that simulated normal urination. Skin on adult forearms and skin in the diaper region of children were concordant in their response to wet diapers. Skin wetness was directly related to the amount of liquid retained in absorbent layers close to the skin.