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To evaluate the evidence in the peer-reviewed literature regarding the use of tear osmolarity as a physiological marker to diagnose, grade severity, and track therapeutic response in dry eye disease (DED). In addition, to review the evidence for the role of tear osmolarity in the pathophysiology of DED and ocular surface disease. A literature review of all publications after the year 2000, which included the keywords \"tear osmolarity\", was conducted. Relevant articles were graded according to quality of evidence and research, using the University of Michigan Practice Guideline and the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) rating systems. Articles were further categorized by the nature of any reported financial support and by the overall impression they provided related to tear osmolarity. A total of 164 articles were identified as relevant to the search criteria, although some were editorials, and some were written in a foreign language. Of the total, it was possible to grade 159, and an overall impression was generated for 163. A positive impression of tear osmolarity in DED diagnosis was evident in 72% (117/163) of all articles, with a neutral impression in a further 21% (35/163); 7% had a negative impression. The percentage of positive impressions appeared independent of the quality of research; 73% (38/52) of articles graded high/moderate quality supported the use of tear film osmolarity measurement in DED diagnosis. Impressions were also independent of the source of financial support, with 72% (75/104) of independent studies positive. The literature broadly supports the use of tear film osmolarity as an objective numerical measure for diagnosing, grading severity, and managing treatment of DED.

Tear hyperosmolarity plays a crucial role in initiation of inflammatory response and damage to ocular surface epithelia. Accurate measurement of tear osmolarity is essential for dry eye. This prospective observational and experimental study was conducted in 182 eyes of 182 participants, including 115 subjects with dry eye (Sjögren syndrome aqueous-deficient dry eye [SS ADDE], non-SS ADDE, and evaporative DE [EDE]), 36 with conjunctivochalasis (CCh), and 31 normal controls (NC). The ocular surface disease index (OSDI), tear meniscus height (TMH), Schirmer I test, tear matrix metalloproteinase-9 (MMP-9), tear breakup time, and ocular staining score were assessed. Tear osmolarity was measured using the TearLab osmolarity system (Escondido, CA, USA) by applying 1.0 μl tears collected by micropipette to the TearLab test card or by direct contact between the test card and the temporal tear meniscus. For in vitro analyses, osmolarity of 271.25, 300, 347.5, and 395 mOsm/L solutions were measured at various volumes (0.2, 0.5, 1.0, 2.0, and 5.0 μl) with a TearLab osmometer. Tear osmolarity measured by direct contact was higher than that measured by micropipette (13.7 ± 10.5 mOsm/L, p  < 0.001). The difference of osmolarities was higher in the non-SS ADDE, SS ADDE, and CCh than in the NC and EDE ( p  < 0.001 for all). Osmolarity was negatively correlated with Schirmer score and TMH (r = − 0.346, p  < 0.001; r = − 0.447, p  < 0.001, respectively). The smaller the sample volume, the higher the measured osmolarity in the in vitro analysis at 300 and 347.5 mOsm/L (r = − 0.659, p  < 0.01; r = − 0.579, p  < 0.05, respectively). The TearLab osmometer tended to report higher tear osmolarity inversely proportional to sample volumes, possibly due to the evaporation effect. Therefore, care should be taken when interpreting tear osmolarity in patients with low tear volume or CCh.

To compare the in vivo precision of two commercially available point-of-care osmometers among normal subjects with no dry eye disease. Twenty healthy adults with healthy ocular surfaces were evaluated by licensed eye care practitioners. All subjects had low Ocular Surface Disease Index score (<5), normal tear breakup time (>10 seconds), and no evidence of corneal fluorescein staining. Five consecutive measurements of tear osmolarity were measured on each eye using each of the two osmometers: the TearLab Osmolarity System (TearLab) and the I-Med i-Pen (i-Pen), for a total of 200 measurements per device. Performance of the osmometers was determined by specificity, estimated by the percentage of osmolarity data at or below the clinical cutoff (308 mOsm/L) and precision, and represented by the standard deviation per subject. In addition, to assess analytical performance, on each day of patient testing, standardized osmolarity quality control solutions (338 mOsm/L) were tested on the TearLab per manufacturer instructions. i-Pen manufacturer instructions do not neither provide for, nor recommend quality control procedures. The mean age of the 20 subjects was 27±8 years (range: 19-48 years, 16 females, four males). Over 2 months of testing, the TearLab reported analytical performance on quality control solutions of 335.8±4.2 mOsm/L with a coefficient of variation of 1.3%. In the subject cohort, 90.9% of TearLab measurements were in the normal range ≤308 mOsm/L. The i-Pen reported 37.5% of all measurements in the normal range. The average intra-subject osmolarity of the TearLab was 295.4±8.6 mOsm/L, which was significantly lower and less variable than the i-Pen, which reported an average of 319.4±20.3 mOsm/L ( <0.001). When the measurements were grouped by subject, the TearLab accurately identified 100% of subjects as normal while the i-Pen accurately identified only 15% of subjects as normal. In this randomized comparative study of two point-of-care osmometers among normal, healthy non-dry eye subjects, the TearLab Osmolarity System demonstrated accuracy, precision, and agreement with clinical interpretation in line with the manufacturer claims. The i-Pen lacked sufficient performance to delineate subjects with and without dry eye disease.

Purpose: This present prospective, cross-sectional study aims to comprehensively evaluate the ocular surface in asymptomatic patients with diffuse blebs after trabeculectomy versus chronic anti-glaucoma medication use and compare it with the age-matched normal population. Methods: Objective clinical evaluation was done by tear film break-up time (TBUT) and Schirmer's test (ST) in the three groups-trabeculectomy >6 months with a diffuse bleb (Wurzburg bleb classification score ≧10), chronic anti-glaucoma medication (AGM >6 months) group, and normal population. In all groups, tear film osmolarity was checked with the TearLab® device (TearLab Corp., CA, USA), and subjective evaluation was performed by administering Ocular Surface Disease Index (OSDI) questionnaire. Patients already on chronic lubricants or any other drug for the treatment of dry eyes (viz. steroids, cyclosporin) or having symptoms suggestive of an abnormal ocular surface, who had undergone refractive or intraocular surgery, and contact lens users were excluded. Results: In total, 104 subjects/eyes were recruited over 6 weeks. Thirty-six eyes recruited in the trab group were compared with 33 eyes studied in the AGM group, and both these groups were compared to 35 normal eyes. When compared to normals, TBUT and ST were significantly lower (P = 0.003 and 0.014) and osmolarity and OSDI were statistically significantly higher (P = 0.007 and 0.003) in the AGM group, whereas only TBUT was statistically significantly different (P = 0.009) when the trab group was compared to normals. Also, when the trab group was compared to the AGM group, ST was found to be higher (P = 0.003) and osmolarity was lower (P = 0.034). Conclusion: To conclude, ocular surface is affected even in asymptomatic patients on AGM but near normalcy is possible following trabeculectomy when blebs are diffuse.

The purpose of this study was to compare the precision and accuracy of commercially available tear film osmometers. Contrived tear solution target values representing the physiological range of tear osmolarity (normal eyes 297 mOsm/L, moderately dry eyes 342 mOsm/L, and severe dry eyes 383 mOsm/L) were constructed using a mix of mono- and divalent electrolytes, metabolites, serum albumin, and pH balanced to 7.4. Solution values were randomized and masked from the investigators during testing. Osmometers (Wescor 5520 Vapro Pressure Osmometer: device A, TearLab Osmolarity System: device B, and i-Med Pharma i-Pen: device C) were calibrated according to manufacturer instructions. Each level was tested 64× on each osmometer across two sites. Accuracy was reported as a correlation coefficient against expected linear dilutions, precision was calculated as percent coefficient of variation. Device A reported a correlation with known solutions of =0.98, with averages of 305.6±4.0, 352.2±5.5, and 389.8±4.0 mOsm/L, and coefficient of variations (CVs) of 1.3%, 1.6%, and 1.0%, respectively. Device B reported an =0.96, with averages of 300.6±3.7, 341.4±7.9, and 376.8±5.1 mOsm/L, and CVs of 1.2%, 2.3%, and 1.4%, respectively. Device C reported an =0.03, with averages of 336.4±21.5, 342.0±20.7, and 345.7±22.0 mOsm/L, and CVs of 6.4%, 6.1%, and 6.4%, respectively. In this randomized, masked, in vitro study, device A and device B had significantly better accuracy and precision in measuring osmolarity of contrived tear solutions of known target values compared to device C. Device C showed insufficient performance to accurately and precisely delineate osmolarity levels in the physiological range. Furthermore, in vivo studies would be required to compare performance in human subjects.

Background Some studies report that increased tear osmolarity is a reliable indicator of dry eye syndrome (DES). The OcuSense TearLab™ osmometer requires less than a 100-nl sample of tears and provides an instant quantitative result. Our aim was to clinically evaluate this instrument in terms of its reproducibility and repeatability. Methods Twenty-nine participants who ranged in age from 19 to 49 years (mean ± SD: 23.3 ± 5.5 years) were recruited. Osmolarity readings were collected by two operators, in two sessions separated by 1 or 2 weeks in order to assess test reproducibility and repeatability. Results The coefficient of reproducibility was 39 mOsms/l; the coefficient of repeatability was 33 mOsms/l. Conclusions Our mean coefficient of variation over four readings for 29 subjects is 2.9%, which compares well with that reported by the manufacturer. Our results inform practitioners about the level of change over time that can be considered clinically relevant for healthy subjects. This value is 33mOsms/l; any change smaller than this could be attributed to measurement noise.

Purpose: The aim of this study is to evaluate the difference between reflex and basal tear osmolarity among healthy normal subjects. Method: The right eyes of 20 healthy normal male subjects aged 20 to 40 years were recruited for this study. The inclusion criteria for the subjects were the Ocular Surface Disease Index questionnaire score of less than 12 and wetting length of the phenol red thread of more than 10 mm. Tear film osmolarity was assessed using TearLab osmometer. Basic tear osmolarity was measured normally without inducing any irritation to the eye. In order to stimulate reflex tear, subjects were asked to open their eye as long as they can till they feel ocular surface irritation (minimum 20 s). Results: The mean score on the Ocular Surface Disease Index questionnaire was 5.5 ± 3. The mean value obtained from the phenol red thread was 21 ± 4.5 mm. There were no statistically significant differences between the osmolarity readings of basal and reflex tear osmolarity (p > 0.05). The mean value was 308 ± 12 and 306 ± 9 mOsm/l for basic and reflex tear osmolarity, respectively. Conclusion: This study found that the osmolarity of the basal and reflex tears fell within the same range. The values found in this study are in agreement with published results for normal subjects.

It is well established that the diagnosis of dry eye is difficult. Tear osmolarity is considered by some to be the only metric of dry eye that is repeatable with some claiming that osmolarity is the best diagnostic metric for dry eye. A recently developed system, the Tearlab osmolarity system, is now available that can give a measure of tear osmolarity in less than 60 seconds. It is important that any new instrument be evaluated for its repeatability and reproducibility. The aim of this study was to investigate the repeatability and reproducibility of the Tearlab system by taking multiple, successive measurements of osmolarity of a manufacturer supplied calibration/test solution. The results of this investigation show that the Tearlab osmolarity system provides reasonably accurate, repeatable and reproducible measurements of tear osmolarity.  (S Afr Optom 2013 72(1) 19-24)