Randomized, masked, in vitro comparison of three commercially available tear film osmometers

Characterizing the Robustness of Distinct Clinical Assessments in Identifying Dry Eye Condition of Animal Models

PURPOSE

The study aims to characterize the robustness of distinct clinical assessments in identifying the underlying conditions of dry eye disease (DED), with a specific emphasis on the involvement of conjunctival goblet cells.

METHODS

Seven rabbits receiving surgical removal of the lacrimal and Harderian glands were divided into two groups, one with ablation of conjunctival goblet cells by topical soaking of trichloroacetic acid (TCA) to the bulbar conjunctiva (n = 3) and one without (n = 4), and the conditions of DED were assessed weekly using Schirmer test, tear breakup time (TBUT), tear osmolarity, and National Eye Institute (NEI) fluorescein staining grading. After 8 weeks, the rabbits were sacrificed, and the eyes were enucleated for histopathological examination.

RESULTS

Histopathological analysis revealed corneal epithelial thinning in both groups. While TCA soaking significantly decreased the density of conjunctival goblet cells, DED rabbits without TCA also showed a partial reduction in goblet cell density, potentially attributable to dacryoadenectomy. Both groups showed significant decreases in Schirmer test and TBUT, as well as an increase in tear osmolarity. In DED rabbits with TCA soaking, tear osmolarity increased markedly, suggesting that tear osmolarity is highly sensitive to loss and/or dysfunction of conjunctival goblet cells. Fluorescein staining was gradually and similarly increased in both groups, suggesting that fluorescein staining may not reveal an early disruption of the tear film until the prolonged progression of DED.

CONCLUSION

The Schirmer test, TBUT, tear osmolarity, and NEI fluorescein grading are distinct, yet complementary, clinical assessments for the evaluation of DED. By performing these assessments in definitive DED rabbit models, both with and without ablation of conjunctival goblet cells, the role of these cells in the homeostasis of tear osmolarity is highlighted. Characterizing the robustness of these assessments in identifying the underlying conditions of DED will guide a more appropriate management for patients with DED.

Role of lymphotoxin alpha as a new molecular biomarker in revolutionizing tear diagnostic testing for dry eye disease

Dry eye disease (DED), primarily classified as multifactorial ocular surface disorder, afflicts tens of millions of individuals worldwide, adversely impacting their quality of life. Extensive research has been conducted on tear film analysis over the past decades, offering a range of tests to evaluate its volume, health, and integrity. Yet, early diagnosis and effective treatment for DED continue to pose significant challenges in clinical settings. Nevertheless, by recognizing key phenomena in DED such as ocular surface inflammation, hyperosmolarity, and tear film instability, this article provides a comprehensive overview of both traditional and recently developed methods for diagnosing and monitoring DED. The information serves as a valuable resource not only for clinical diagnosis but also for further research into DED.

Randomized comparison of in vivo performance of TearLab® and I-PEN® osmometry in normal dogs

OBJECTIVE

To compare tear film (TF) osmolarity measured using TearLab® and I-PEN® osmometers in the same dogs without any ocular surface disease.

ANIMAL STUDIED

Fifty-two dogs (98 eyes) of different breeds were evaluated.

PROCEDURES

Tear film (TF) osmolarity was evaluated at 2-min intervals. The test was randomly determined, and single measurements were performed using each osmometer. Subsequently, complete ophthalmologic examinations were performed based on Schirmer tear test-1 (STT-1) analysis, tear film breakup time (TFBUT), and slit-lamp biomicroscopy. For each osmometer, the mean ± standard deviation of the TF osmolarity was calculated, and a paired Student's t-test was used to compare the values obtained. Pearson correlation analysis was performed to assess the association between osmolarity and other values such as STT-1, TFBUT, and age.

RESULTS

Tear film osmolarity determined using TearLab® (340.42 ± 15.87 mOsm/L) and I-PEN® (321.58 ± 17.39 mOsm/L) were significantly different (p < .001). However, statistical significance could not be confirmed between osmolarity and other values, such as STT-1, TFBUT, and age.

CONCLUSIONS

In dogs, the TF osmolarity values obtained using TearLab® tend to be higher than those obtained using I-PEN®, contrary to that observed in humans. These findings can serve as a reference for establishing normal values for each osmometer for clinical use in measuring TF osmolarity in dogs.

Evaluation of suitability and detection range of fluorescent dye-loaded nanoliposomes for sensitive and rapid sensing of wide ranging osmolarities

Measurement of osmolarity is critical for optimizing bioprocesses including antibody production and detecting pathologies. Thus, rapid, sensitive, and in situ sensing of osmolarity is desirable. This study aims to develop and assess the suitability of calcein- and sulforhodamine-loaded nanoliposomes for ratiometric sensing of osmolarity by fluorescence spectroscopy and evaluate the range of detection. The detection is based on concentration-dependent self-quenching of calcein fluorescence (sensor dye at 6-15 mM) and concentration-independent fluorescence of sulforhodamine (reference dye) due to osmotic shrinkage of the nanoliposomes when exposed to hyperosmotic solutions. Using mathematical modeling, 6 mM calcein loading was found to be optimal to sense osmolarity between 300 and 3000 mOsM. Calcein (6 mM)- and sulforhodamine (2 mM)-loaded nanoliposomes were produced by thin-film hydration and serial extrusion. The nanoliposomes were unilamellar, spherical (108 ± 9 nm), and uniform in size (polydispersity index [PDI] 0.12 ± 0.04). Their shrinkage induced by exposure to hyperosmotic solutions led to rapid self-quenching of calcein fluorescence (F_Green), but no effect on sulforhodamine fluorescence (F_Red) was observed. F_Green/F_Red decreased linearly with increasing osmolarity, obeying Boyle van't Hoff's relationship, thus proving that the nanoliposomes are osmosensitive. A calibration curve was generated to compute osmolarity based on F_Green/F_Red measurements. As a proof-of-concept, dynamic changes in osmolarity in a yeast-based fermentation process was demonstrated. Thus, the nanoliposomes have great potential as sensors to rapidly and sensitively measure wide-ranging osmolarities.

Assessment of Tear Osmolarity in Smokers Using TearLab and I-Pen Systems

Purpose. Smoking has a negative effect on health and ocular tear film. The purpose of the current study is to investigate the correlation between the TearLab and I-Pen osmolarity scores in smokers and compare them with those of non-smoking healthy males. Methods. Thirty male smokers (25.3 ± 2.2 years) participated in the study. An age-matched (22.9 ± 2.0 years) control group of non-smoking healthy males (N = 30) was also recruited for comparison purposes. The ocular surface disease index (OSDI) was completed first, followed by the TearLab and I-Pen osmolarity measurements. Results. The median TearLab osmolarity score was lower (P < 0.001) than that obtained using the I-Pen in both the study and the control groups. The OSDI scores and osmolality measurements were higher (P < 0.001) in smokers than in the control subjects. In the smoker group, there were moderate correlations between the OSDI scores and the measurements obtained using the TearLab (Spearman’s correlation coefficient, r = 0.463; P = 0.010) and I-Pen (r = 0.449; P = 0.013) systems. In addition, there was a strong correlation between the osmolarity scores obtained from the TearLab and I-Pen systems in smokers (r = 0.911; P < 0.001). Conclusion. The I-Pen scores in smokers were significantly higher than those obtained using TearLab. The TearLab scores showed small variations compared with those obtained using I-Pen. A strong correlation was found between the TearLab and I-Pen scores in smokers. The osmolarity TearLab and I-Pen scores were significantly higher in smokers compared with normal eye subjects.

Diurnal variations of tear film osmolarity on the ocular surface

The measurement of tear film osmolarity has been suggested as a gold standard in the diagnosis of dry eye. Many tear film physiological variables oscillate during the day. This review summarises current clinical knowledge regarding diurnal osmolarity variation in the tear film. A critical analysis is presented in respect of of sample size and characteristics, differences in the diurnal osmolarity variation on healthy versus altered tear film conditions or environment, and time of day and number of measurements undertaken. A comparison of 21 studies was made for studies in which one of the main objectives was to analyse the variance of tear film osmolarity at different time-points in a day on human cohorts. Tear film osmolarity appeard to be somewhat influenced by the time of day in healthy subjects and patients with ocular surface disease, or altered by environmental conditions. Both healthy and non-physiological tear film cohorts showed variations in results depending on the study: no variations during the day or statistically different values at some point in the day. These differences could be in the middle of the day or between the beginning and the end of the day, with higher values in the morning than in the afternoon, or even the opposite situation. The possibility of diurnal variations in tear film osmolarity should be considered by the clinician since the time of day when the tear film measurements are made can be critical in making the right diagnosis. Future studies in the diurnal variation field may have to use a well-established range of measurement time-points and a larger group of healthy subjects and and subjects who have a tear film altered by pathological or environmental conditions.

The validity of point of care tear film osmometers in the diagnosis of dry eye

PURPOSE

To determine the repeatability of TearLab and I-PEN osmometers in vivo and their accuracy in vitro.

DESIGN

Prospective, single-visit study.

METHODS

The tear osmolarity of 28 participants was evaluated with TearLab and I-PEN on two occasions in random order, over a 2-h period. Both eyes were measured in a randomised order. Coefficients of repeatability (CoR) were determined for each device, together with the bias and limits of agreement between them. For the in vitro experiment, the osmolarity was measured by both osmometers in five solutions (290, 297, 342, 338 and 383 mOsm/L) at two different temperatures (22 and 37°C) with a total of four consecutive measures.

RESULTS

The CoRs for the TearLab and I-PEN in the right and left eyes were 26.2, 21.3, 33.6 and 28.3 mOsm/L, respectively. Across the first and second repeats, TearLab showed consistency of diagnosis for 50% of participants with 29% as dry eye positive, while I-PEN indicated 68% consistency of diagnosis with 57% dry eye positive. The instruments agreed on the diagnosis in 46.5% of cases. In vitro comparison showed that the average measurement errors for TearLab and I-PEN were -10 ± 13 and 31 ± 39 mOsm/L at 22°C, and 4 ± 13 and 20 ± 51 mOsm/L at 37°C.

CONCLUSIONS

In vitro, both instruments showed reasonable accuracy and repeatability at mid-range osmolarities, but repeatability generally declined at higher and lower levels. While TearLab accuracy remained consistent across the osmolarity range, measurement errors for I-PEN noticeably increased outside the mid-range. In vivo, both instruments displayed poor repeatability. This casts doubt on the value of utilising either instrument to establish osmolarity as a factor in the diagnosis of dry-eye, according to currently recommended diagnostic guidelines (TFOS DEWS II), if only a single measurement is taken from each eye.

Evaluation of tear osmolarity measured by I-Pen osmolarity system in patients with dry eye

This retrospective comparative study was to evaluate tear osmolarity measured by I-Pen osmolarity system (I-MED Pharma Inc, Dollard-des-Ormeaux, Quebec, Canada) in healthy subjects without dry eye disease (DED) and patients with DED, and its association with other ocular surface parameters. This study comprised 65 eyes of 65 patients. The ocular surface parameters including tear osmolarity with I-Pen osmometer of the patients who visited the refractive surgery center of Samsung Medical Center between January 1, 2020 and May 31, 2020 were retrospectively collected. The subjects were divided as asymptomatic normal group and symptomatic dry eye group. The distribution of tear osmolarity and its association with other ocular surface parameters were evaluated. Total thirty-two patients (32 eyes) were included in the control group, and 33 patients (33 eyes) were included in the DED group. Tear osmolarity was significantly higher in the DED group. Tear osmolarity was negatively correlated with tear break-up time, and the Schirmer test, and was positively correlated with Ocular Surface Disease Index symptom score. The cut-off value of 318 mOsm/L showed a sensitivity of 90.9% and specificity of 90.6% for diagnosing DED. The I-Pen osmometer can be considered suitable for use in the clinical setting, with good performance in DED diagnosis.

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

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.

Investigation of the repeatability of tear osmolarity using an I-PEN osmolarity device

PURPOSE:

To investigate the repeatability of tear osmolarity in healthy Saudi subjects using an I-PEN osmolarity device.

MATERIALS AND METHODS:

Thirty typical male subjects with healthy eyes (27.4 ± 4.9 years) participated in the study. Eye abnormalities were tested with a slit lamp, and eye comfort was determined with the surface disease index. Measurements of the tear break-up time and phenol red thread tests were used for as exclusion criteria. The tear osmolarity test, using an I-PEN osmolarity system, was performed three times in the right eye of each subject with a 5 min' gap between tests.

RESULTS:

The average osmolarity test score was 303.8 ± 4.8 mOsm/L. Tear osmolarity measurements showed tear osmolarity of 280–299 mOsm/L, 300–309 mOsm/L, and 310–329 mOsm/L in 14 (46.7%), three (10%), and 13 (43.3%) subjects, respectively. Correlations among the three I-PEN measurements were significant (Spearman's correlation coefficient; r = 0.036, 0.501, and 0.603; P = 0.050, 0.006, and 0.001, respectively). The mean coefficient of variance among the three measurements was 4.4%.

CONCLUSION:

The mean measurement of an I-PEN tear osmolarity was 303.8 ± 4.8 mOsm/L which is in agreement with the range of those reported for healthy subjects. The I-PEN is reliable and has the advantage of portability (hand-held) compared to the other osmolarity systems.

Tear Film Osmolarity Measurement in Japanese Dry Eye Patients Using a Handheld Osmolarity System

We studied the efficacy and safety of a handheld osmolarity measurement system (I-PEN) in Japanese patients with dry eye disease (DED) and non-DED subjects. In this prospective, multicenter study, tear osmolarity was examined using the I-PEN in a total of 122 eyes divided into DED (n = 71) and non-DED (n = 51) groups. Subjective symptoms were assessed using the Dry Eye-Related Quality-of-Life Score (DEQS) questionnaire. Ocular surface condition was evaluated in terms of fluorescein tear breakup time (FBUT) and tear breakup pattern (TBUP), and by fluorescein staining and Schirmer's test. The I-PEN measurements were performed safely in the majority of cases. There was no statistically significant difference in mean tear film osmolarity between the DED and non-DED groups (294.76 ± 16.39 vs. 297.76 ± 16.72 mOsms/L, respectively, p = 0.32). No significant correlations were observed between osmolarity values and DEQS score, FBUT, or the Schirmer score. Osmolarity did not differ among TBUP subgroups. This prospective clinical study found no correlations between the tear film osmolarity values obtained with the I-PEN system and any subjective or objective parameters of DED. Further studies are required to determine the utility of the I-PEN system in other settings.

Does Oxygen Uptake Before Physical Exercise Affect Tear Osmolarity?

Recently, it has been reported that tear osmolarity (Tosm) is correlated with plasma osmolarity and will increase during exertion. We aimed to assess whether inhaling oxygen-enriched air between exercises could significantly change the Tosm value. Thirty men aged 24.9 years were included in the study. A cycloergometer was used to perform the exercise protocol. We recorded the participants’ Tosm (mOsm/L), heart rate (HR, beats/minute), oxygen saturation, and blood pressure values. After the first exhaustive exercise (T1), participants inhaled oxygen in the experimental group and a placebo in the control group. After the second exercise (T2), another set of measurements was obtained. The Tosm value before exercise was 297.4 ± 1.21 and 296.53 ± 1.11 mOsm/L (p = 0.61718) and the HR was 72.6 ± 2.59 and 73 ± 2.59 beats/minute (p = 0.39949) in the study and the control group, respectively. At T1, Tosm was 303.67 ± 1.25 and 302.2 ± 1.25 mOsm/L (p = 0.41286) and the HR reached 178.04 ± 2.60 and 176.4 ± 2.60 beats/minute (p = 0.65832), respectively. At T2, Tosm in the study group reached 305.73 ± 0.86 mOsm/L (correlation with the use of oxygen: r = −0.3818), and in the control group, it was 308.4 ± 0.86 mOsm/L (p = 0.0373), while the HR reached 172.20 ± 2.53 beats/minute in the study group and 178.2 ± 2.53 beats/minute in the control group (p = 0.057). It was concluded that inhaling oxygen before and after exercise could increase the rate of recovery after exhaustive exercise.

New approaches for diagnosis of dry eye disease

We reviewed the literature for different diagnostic approaches for dry eye disease (DED) including the most recent advances, contradictions and promising diagnostic tools and technique. We performed a broad literature search for articles discussing different methods for diagnosis of DED including assessment of tear osmolarity, tear film stability, ocular biomarkers and others. Articles indexed in PubMed and google scholar were included. With the growing cosmetic industry, environmental pollution, and booming of digital screens, DED is becoming more prevalent. Its multifactorial etiology renders the diagnosis challenging and invites the emergence of new diagnostic tools and tests. Diagnostic tools can be classified, based on the parameter they measure, into tear film osmolarity, functional visual acuity, tear volume, tear turnover, tear film stability, tear film composition, ocular biomarkers and others. Although numerous methods exist, the most accurate diagnosis can be reached through combining the results of more than one test. Many reported tests have shown potential as diagnostic/screening tools, however, require more research to prove their diagnostic power, alone or in combination. Future research should focus on identifying and measuring parameters that are the most specific to DED diagnosis.

Dry Eye Disease: Emerging Approaches to Disease Analysis and Therapy

Dry eye disease (DED) is among the most common ocular disorders affecting tens of millions of individuals worldwide; however, the condition remains incompletely understood and treated. Valuable insights have emerged from multidisciplinary approaches, including immunometabolic analyses, microbiome analyses, and bioengineering. Furthermore, we have seen new developments in clinical assessment approaches and treatment strategies in the recent past. Here, we review the emerging frontiers in the pathobiology and clinical management of DED.

Dry eye is matched by increased intrasubject variability in tear osmolarity as confirmed by machine learning approach

OBJECTIVE

Because of high variability, tear film osmolarity measures have been questioned in dry eye assessment. Understanding the origin of such variability would aid data interpretation. This study aims to evaluate osmolarity variability in a clinical setting.

MATERIAL AND METHODS

Twenty dry eyes and 20 control patients were evaluated. Three consecutive osmolarity measurements per eye at 5min intervals were obtained. Variability was represented by the difference between both extreme readings per eye. Machine learning techniques were used to quantify discrimination capacity of tear osmolarity for dry eye.

RESULTS

Mean osmolarities in the control and dry eye groups were 295.1±7.3mOsm/L and 300.6±11.2mOsm/L, respectively (P=.004). Osmolarity variabilities were 7.5±3.6mOsm/L and 16.7±11.9mOsm/L, for the control and dry eye groups, respectively (P<.001). Based on osmolarity, a logistic classifier showed an 85% classification accuracy.

CONCLUSIONS

In the clinical setting, both mean osmolarity and osmolarity variability in the dry eye group were significantly higher than in the control group. Machine learning techniques showed good classification accuracy. It is concluded that higher variability of tear osmolarity is a dry eye feature.

Validity and Reliability of a Novel Handheld Osmolarity System for Measurement of a National Institute of Standards Traceable Solution

PURPOSE

To evaluate the validity and reliability of a novel handheld osmolarity system (I-PEN Osmolarity System; I-MED Pharma Inc, Dollard-des-Ormeaux, Quebec, Canada) for measurement of the osmolarity of a National Institute of Standards and Technology (NIST) traceable solution at a variety of ambient temperatures.

METHODS

A total of 65 measurements of an NIST solution with a verified osmolarity of 290 ± 2 mOsmol/L were taken using 3 separate handheld osmolarity systems, 65 unique single-use sensors (SUSs) from 3 different lots, and 2 adaptors. Mean values were calculated using the device, SUS, and adaptor. Measurements were taken using a handheld osmolarity system, an adaptor, and 56 individual SUSs at 6 different ambient temperatures ranging from 17.7 to 26.5°C.

RESULTS

Overall, the mean osmolarity measured was 294.06 mOsmol/L (SD ±2.29; percent coefficient of variation 0.78), ranging from 286.60 to 298.18 mOsmol/L. This fell within a prespecified acceptable variability of ±4 mOsmol/L (SD ±7). Mean values did not vary across devices, adaptors, or single-use sensors used. Mean osmolarity measurements increased with rising ambient temperatures, with an R = 0.88. The temperature correction factor was calculated to be 2.01 mOsmol/L per °C.

CONCLUSIONS

The osmolarity system reliably and accurately measured the osmolarity of an NIST solution in a laboratory setting, using an adaptor to correct for differences in resistance between a laboratory NIST solution measurement and direct measurements on the palpebral conjunctiva of the eyelid. The handheld osmolarity system represents a rapid and accurate instrument for measurement of tear osmolarity in a simulated testing setting.

Randomized comparison of in vivo performance of two point-of-care tear film osmometers

PURPOSE

To compare the in vivo precision of two commercially available point-of-care osmometers among normal subjects with no dry eye disease.

METHODS

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.

RESULTS

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 (P<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.

CONCLUSION

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.

The Growing Need for Validated Biomarkers and Endpoints for Dry Eye Clinical Research

Purpose

Biomarkers with minimally invasive and reproducible objective metrics provide the key to future paradigm shifts in understanding of the underlying causes of dry eye disease (DED) and approaches to treatment of DED. We review biomarkers and their validity in providing objective metrics for DED clinical research and patient care.

Methods

The English-language literature in PubMed primarily over the last decade was surveyed for studies related to identification of biomarkers of DED: (1) inflammation, (2) point-of-care, (3) ocular imaging, and (4) genetics. Relevant studies in each group were individually evaluated for (1) methodological and analytical details, (2) data and concordance with other similar studies, and (3) potential to serve as validated biomarkers with objective metrics.

Results

Significant work has been done to identify biomarkers for DED clinical trials and for patient care. Interstudy variation among studies dealing with the same biomarker type was high. This could be attributed to biologic variations and/or differences in processing, and data analysis. Correlation with other signs and symptoms of DED was not always clear or present.

Conclusions

Many of the biomarkers reviewed show the potential to serve as validated and objective metrics for clinical research and patient care in DED. Interstudy variation for a given biomarker emphasizes the need for detailed reporting of study methodology, including information on subject characteristics, quality control, processing, and analysis methods to optimize development of nonsubjective metrics. Biomarker development offers a rich opportunity to significantly move forward clinical research and patient care in DED.

Overview

DED is an unmet medical need - a chronic pain syndrome associated with variable vision that affects quality of life, is common with advancing age, interferes with the comfortable use of contact lenses, and can diminish results of eye surgeries, such as cataract extraction, LASIK, and glaucoma procedures. It is a worldwide medical challenge with a prevalence rate ranging from 8% to 50%. Many clinicians and researchers across the globe are searching for better answers to understand the mechanisms related to the development and chronicity of DED. Though there have been many clinical trials for DED, few new treatments have emerged over the last decade. Biomarkers may provide the needed breakthrough to propel our understanding of DED to the next level and the potential to realize our goal of truly personalized medicine based on scientific evidence. Clinical trials and research on DED have suffered from the lack of validated biomarkers and less than objective and reproducible endpoints. Current work on biomarkers has provided the groundwork to move forward. This review highlights primarily ocular biomarkers that have been investigated for use in DED, discusses the methodologic outcomes in providing objective metrics for clinical research, and suggests recommendations for further work.