Utility of Tear Osmolarity Measurement in Diagnosis of Dry Eye Disease.

The prevalence of dry eye disease is high worldwide and poses a great burden on patients' daily lives. Accurate diagnosis of the disease is important, and it requires application of various methods. Hyperosmolarity is believed to be the disease marker and thus measuring it provides useful information. In this study we investigated utility of tear osmolarity measured with TearLab osmometer, along with other diagnostic tests (Ocular Surface Disease Index questionnaire, Tear film break-up time, Ocular Protection Index, Ocular Surface Staining, Schirmer I test, Meibomian gland functionality in 757 patients (1514 eyes) with dry eye disease and 29 healthy controls (58 eyes). Statistical differences between the patient group and the control group were observed for all the tests apart from tear osmolarity, regardless of cut-off value (>308 mOsm/L, >316 mOsm/L, and inter-eye difference >8 mOsm/L). Moreover, in the receiver operating characteristics curve analyses tear osmolarity measurement could not discriminate dry eye disease pathological scores. Therefore, our study suggests that tear osmolarity measured with TearLab osmometer cannot be used as a key indicator of DED.

Calculated Versus Measured Urine Osmolarity: Accuracy of Estimated Urine Density.

BACKGROUND: Urine osmolarity (OsmU) is the gold standard for the evaluation of the kidney's urine concentration capacity; nevertheless, urinary density (UD) is often used as a surrogate for its estimation. OBJECTIVE: The objective of this study was to analyze the accuracy of UD in estimating OsmU. MATERIALS AND METHODS: A transversal study including patients with simultaneous determination of UD measured with refractometry and OsmU measured by osmometer (OsmUm). We multiplied the last two digits of the UD by 35, 30, 32, 33.5, and 40 to estimate OsmU; the estimates were considered precise if the value was ± 30 mOsm/kg from the OsmUm. A Bland-Altman analysis was conducted. RESULTS: Among 205 patients, there was no difference between OsmUm and the estimated form when using a factor of 33.5 (p = 0.578). When analyzing by the absence or presence of proteinuria and/or glycosuria, there were no differences when using the factors 35 (p = 0.844) and 32 with adjusted UD (p = 0.898). In the linear correlation analysis, values for Pearson's r = 0.788 and r2 = 0.621 were obtained (p < 0.001). The areas under the curve obtained by the receiver operating characteristics curves to estimate urine osmolarity values < 100 and > 600 mOsm/kg were > 0.90. CONCLUSION: The estimation of the OsmU from UD showed adequate performance. If an osmometer is unavailable, we recommend using the factor 35 for clean samples and 32 with adjusted UD for samples with proteinuria and/or glycosuria.

[New approaches to the treatment of keratoconjunctivitis sicca]. / Novye podkhody k lecheniiu sukhogo keratokon''iunktivita.

A new method has been developed for the treatment of severe forms of keratoconjunctivitis sicca (KCS) that involves the use of an original cyclosporine A (CyA) saturated soft contact lens (SCL) together with preservative-free artificial tears therapy. AIM: to evaluate the effectiveness of the newly developed treatment for KCS based on the use of medical SCL saturated with 0.05% CyA. MATERIAL AND METHODS: The patients (43 men, 60 eyes) with severe KCS were divided into 2 groups. Group 1 included 21 patients (30 eyes), who received artificial tears and wore 0.05% CyA-saturated silicone-hydrogel SCLs. Group 2 included 22 patients (30 eyes), who wore unsaturated original SCLs and received CyA instillations 2 times daily and, also, artificial tears. Apart from a standard ophthalmic examination, the assessment included Schirmer's test, Norn's test, vital eye stain tests, tear osmometry, laser confocal tomography of the cornea, optical coherence tomography of the anterior segment with meniscometry, impression cytology of the conjunctiva, tear pH measurement, plating of the content of the conjunctival cavity, measurement of the width of the palpebral fissure, and calculation of the ocular surface disease index. Treatment results were followed up at 1, 3, 6, and 12 months. RESULTS: The use of 0.05% CyA-saturated SCLs allows to halve treatment time for patients with severe KSC (down to 1 week - 1 month) as compared to unsaturated original SCLs in combination with 0.05% CyA instillations and to reduce it 5 times as compared to 0.05% CyA instillations only. CONCLUSION: The new method of KSC treatment that involves the use of medical SCL of original design (ensures even distribution of 0.05% CyA across the ocular surface) and preservative-free artificial tears has demonstrated high therapeutic effectiveness as compared to existing methods.

Calculating osmotic pressure of glucose solutions according to ASOG model and measuring it with air humidity osmometry.

The osmotic pressure of glucose solution at a wide concentration range was calculated using ASOG model and experimentally determined by our newly reported air humidity osmometry. The measurements from air humidity osmometry were compared with the well-established freezing point osmometry and ASOG model calculations at low concentrations and with only ASOG model calculations at high concentrations where no standard experimental method could serve as a reference for comparison. Results indicate that air humidity osmometry measurements are comparable to ASOG model calculations at a wide concentration range, while at low concentrations freezing point osmometry measurements provide better comparability with ASOG model calculations.

Apoplastic water fraction and rehydration techniques introduce significant errors in measurements of relative water content and osmotic potential in plant leaves.

Relative water content (RWC) and the osmotic potential (π) of plant leaves are important plant traits that can be used to assess drought tolerance or adaptation of plants. We estimated the magnitude of errors that are introduced by dilution of π from apoplastic water in osmometry methods and the errors that occur during rehydration of leaves for RWC and π in 14 different plant species from trees, grasses and herbs. Our data indicate that rehydration technique and length of rehydration can introduce significant errors in both RWC and π. Leaves from all species were fully turgid after 1-3 h of rehydration and increasing the rehydration time resulted in a significant underprediction of RWC. Standing rehydration via the petiole introduced the least errors while rehydration via floating disks and submerging leaves for rehydration led to a greater underprediction of RWC. The same effect was also observed for π. The π values following standing rehydration could be corrected by applying a dilution factor from apoplastic water dilution using an osmometric method but not by using apoplastic water fraction (AWF) from pressure volume (PV) curves. The apoplastic water dilution error was between 5 and 18%, while the two other rehydration methods introduced much greater errors. We recommend the use of the standing rehydration method because (1) the correct rehydration time can be evaluated by measuring water potential, (2) overhydration effects were smallest, and (3) π can be accurately corrected by using osmometric methods to estimate apoplastic water dilution.

Cross-validation of the osmotic pressure based on Pitzer model with air humidity osmometry at high concentration of ammonium sulfate solutions.

The osmotic pressure of ammonium sulfate solutions has been measured by the well-established freezing point osmometry in dilute solutions and we recently reported air humidity osmometry in a much wider range of concentration. Air humidity osmometry cross-validated the theoretical calculations of osmotic pressure based on the Pitzer model at high concentrations by two one-sided test (TOST) of equivalence with multiple testing corrections, where no other experimental method could serve as a reference for comparison. Although more strict equivalence criteria were established between the measurements of freezing point osmometry and the calculations based on the Pitzer model at low concentration, air humidity osmometry is the only currently available osmometry applicable to high concentration, serves as an economic addition to standard osmometry.

Determining osmotic pressure of drug solutions by air humidity in equilibrium method.

OBJECTIVE: To establish a new osmotic pressure measuring method with a wide measuring range. METHOD: The osmotic pressure of drug solutions is determined by measuring the relative air humidity in equilibrium with the solution. The freezing point osmometry is used as a control. RESULTS: The data obtained by the proposed method are comparable to those by the control method, and the measuring range of the proposed method is significantly wider than that of the control method. CONCLUSION: The proposed method is performed in an isothermal and equilibrium state, so it overcomes the defects of the freezing point and dew point osmometries which result from the heterothermal process in the measurement, and therefore is not limited to diluted solutions.

Calculating osmotic pressure of xylitol solutions from molality according to UNIFAC model and measuring it with air humidity osmometry.

The osmotic pressure of xylitol solution at a wide concentration range was calculated according to the UNIFAC model and experimentally determined by our newly reported air humidity osmometry. The measurements from air humidity osmometry were compared with UNIFAC model calculations from dilute to saturated solution. Results indicate that air humidity osmometry measurements are comparable to UNIFAC model calculations at a wide concentration range by two one-sided test and multiple testing corrections. The air humidity osmometry is applicable to measure the osmotic pressure and the osmotic pressure can be calculated from the concentration.

In situ osmometry: validation and effect of sample collection technique.

PURPOSE: To compare tear film osmolarity measurements between in situ and vapor pressure osmometers. Repeatability of in situ measurements and the effect of sample collection techniques on tear film osmolarity were also evaluated. METHODS: Osmolarity was measured in one randomly determined eye of 52 healthy participants using the in situ (TearLab Corporation, San Diego, CA) and the vapor pressure (Vapro 5520; Wescor, Inc., Logan, UT) osmometers. In a subset of 20 participants, tear osmolarity was measured twice on-eye with the in situ osmometer and was additionally determined on a sample of nonstimulated collected tears (3 µL) with both instruments. RESULTS: Mean (SD) tear film osmolarity with the in situ osmometer was 299.2 (10.3) mOsmol/L compared with 298.4 (10) mmol/kg with the vapor pressure osmometer, which correlated moderately (r = 0.5, P < 0.05). Limits of agreement between the two instruments were -19.7 to +20.5 mOsmol/L. Using collected tears, measurements with the vapor pressure osmometer were marginally higher (mean [SD], 303.0 [11.0] vs 299.3 [8.0] mOsmol/L; P > 0.05) but correlated well with those using the in situ osmometer (r = 0.9, P < 0.05). The mean (SD) osmolarity of on-eye tears was 5.0 (6.6) mOsmol/L higher than that of collected tears, when both measurements were conducted with the in situ osmometer. This was a consistent effect because the measurements correlated well (r = 0.65, P < 0.05).The in situ osmometer showed good repeatability with a coefficient of repeatability of 9.4 mOsmol/L (r = 0.8, P < 0.05). CONCLUSIONS: Correlation between the two instruments was better when compared on collected tear samples. Tear film osmolarity measurement is influenced by the sample collection technique with the osmolarity of on-eye tears being higher than that of collected tears. This highlights the importance of measuring tear film osmolarity directly on-eye. The in situ osmometer has good repeatability for conducting this measurement.

A needle micro-osmometer for determination of glycosaminoglycan concentration in excised nucleus pulposus tissue.

PURPOSE: Aggrecan is one of the major macromolecular components of the intervertebral disc (IVD) and its loss is an early sign of degeneration. Restoration of aggrecan, and hence of biomechanical properties, is a major objective of biological therapies. At present, assessment of aggrecan concentration via its glycosaminoglycan (GAG) content is accomplished using biochemical and histological methods which require sacrifice of tissue. A minimally invasive method for assessing GAG, and hence aggrecan, which can avoid destruction of tissue, would be of benefit. METHODS: We have developed a needle micro-osmometer that is capable of measuring flux of saline into excised human nucleus pulposus (NP) tissue. Using the isotropic osmotic stress technique to assess the swelling pressure of the excised NP tissue and assuming negligible collagen tensile stress, we were able to relate the flux to the tissue fixed charge density (FCD). GAG concentration is evaluated from its FCD via the radioactive tracer technique. Samples representing different ages (28-59 years) and degeneration grades (1-4) were analyzed. RESULTS: The flux is controlled by both the osmotic pressure difference across the probe's semi-permeable membrane and by the tissue permeability. A linear correlation was found between flux and the tissue FCD. The equation describing the linear fit is FCD/(total tissue hydration) = 1.97 × 10(-4) + 8283 × flux (R = 0.836, p < 10(-4)). Thus, by measuring saline flux, the concentration of GAG can be determined. CONCLUSIONS: Micro-osmometry provides a reliable and minimally invasive tool for assessing GAG content in excised NP tissue. This method may be usefully applied in tissue engineering applications. It may also be useful for in vivo measurements if the question of the degenerative effect of needle puncture can be overcome.