Tear instability importance, mechanisms, validity and reliability of assessment

One Soul and Several Faces of Evaporative Dry Eye Disease

The ocular surface system interacts with, reacts with, and adapts to the daily continuous insults, trauma, and stimuli caused by direct exposure to the atmosphere and environment. Several tissue and para-inflammatory mechanisms interact to guarantee such an ultimate function, hence maintaining its healthy homeostatic equilibrium. Evaporation seriously affects the homeostasis of the system, thereby becoming a critical trigger in the pathogenesis of the vicious cycle of dry eye disease (DED). Tear film lipid composition, distribution, spreading, and efficiency are crucial factors in controlling water evaporation, and are involved in the onset of the hyperosmolar and inflammatory cascades of DED. The structure of tear film lipids, and subsequently the tear film, have a considerable impact on tears' properties and main functions, leading to a peculiar clinical picture and specific management.

Agreement between invasive and noninvasive measurement of tear film breakup time

The agreement between fluorescein breakup time (FBUT) estimates and noninvasive breakup time (NIBUT) estimates automatically acquired using two videokeratoscopes was assessed. Small-cone (E300, Medmont) and large-bowl (K5M, OCULUS) Placido-ring-based videokeratoscopes were utilized for automated NIBUT estimation and fluorescein strip method was used for FBUT estimation. 33 subjects completed the study. Clear instructions were given regarding the blink before measurements. Bland-Altman analysis was used to test the agreement between tear film breakup time estimates and repeated measure analysis of variance was used to test the differences between measurement types. In comparison to FBUT, E300 NIBUT estimate was shorter (- 0.6 ± 2.6 s), whereas K5M NIBUT estimate was longer (3.3 ± 2.4 s). Limits of agreement for FBUT vs. E300 was 29.8 s, for FBUT vs. K5M 26.4 s, and 31.4 s for E300 vs. K5M. There were significant differences between tear film breakup times (F = 3.59, df = 2, P = 0.032). E300 and K5M NIBUT measurements have poor agreement with FBUT, even when blinking is precisely clarified. Agreement was better for shorted break up times than that for longer ones but in general NIBUT measurements are not interchangeable.

Lectin-Based Affinity Enrichment and Characterization of N-Glycoproteins from Human Tear Film by Mass Spectrometry

The glycosylation of proteins is one of the most common post-translational modifications (PTMs) and plays important regulatory functions in diverse biological processes such as protein stability or cell signaling. Accordingly, glycoproteins are also a consistent part of the human tear film proteome, maintaining the proper function of the ocular surface and forming the first defense barrier of the ocular immune system. Irregularities in the glycoproteomic composition of tear film might promote the development of chronic eye diseases, indicating glycoproteins as a valuable source for biomarker discovery or drug target identification. Therefore, the present study aimed to develop a lectin-based affinity method for the enrichment and concentration of tear glycoproteins/glycopeptides and to characterize their specific N-glycosylation sites by high-resolution mass spectrometry (MS). For method development and evaluation, we first accumulated native glycoproteins from human tear sample pools and assessed the enrichment efficiency of different lectin column systems by 1D gel electrophoresis and specific protein stainings (Coomassie and glycoproteins). The best-performing multi-lectin column system (comprising the four lectins ConA, JAC, WGA, and UEA I, termed 4L) was applied to glycopeptide enrichment from human tear sample digests, followed by MS-based detection and localization of their specific N-glycosylation sites. As the main result, our study identified a total of 26 N glycosylation sites of 11 N-glycoproteins in the tear sample pools of healthy individuals (n = 3 biological sample pools). Amongst others, we identified tear film proteins lactotransferrin (N497 and N642, LTF), Ig heavy chain constant α-1 (N144 and 340, IGHA1), prolactin-inducible protein (N105, PIP), and extracellular lacritin (N105, LACRT) as highly reliable and significant N glycoproteins, already associated with the pathogenesis of various chronic eye diseases such as dry eye syndrome (DES). In conclusion, the results of the present study will serve as an important tear film N-glycoprotein catalog for future studies focusing on human tear film and ocular surface-related inflammatory diseases.

Rear 4-min Schirmer test, a modified indicator of Schirmer test in diagnosing dry eye

This study aims to investigate the reliability and efficacy of rear 4-min Schirmer test, as a supplement indicator, in assessing tear secretion and diagnosing dry eye. 180 participants were enrolled in this study. Schirmer test I without anaesthesia was performed once on both eyes to determine the value of normal Schirmer test. The values of tear secretion were recorded at each minute. Other examinations included the following: the ocular surface disease index (OSDI), the standard patient evaluation of eye dryness (SPEED), fluorescein stain, tear film break-up time (BUT), and Meibomian gland (MG) secretion grading. The participants were divided into dry eye (DE) group and non-dry eye (ND) group. The values of the 2-min Schirmer test, rear 3-min Schirmer test, rear 4-min Schirmer test, and 5-min Schirmer test were 5.36 ± 4.63, 5.57 ± 2.11, 7.21 ± 4.13, and 10.93 ± 6.30, respectively, in the DE group. These indicators were 8.25 ± 6.80, 2.73 ± 2.31, 7.36 ± 3.42, and 11.84 ± 6.16, respectively, in the ND group. The rear 4-min Schirmer test had a significant correlation with OSDI and SPEED in the DE group (r =  − 0.242/ − 0.183) and in the ND group (r =  − 0.316/ − 0.373). Meanwhile, the rear 4-min Schirmer test had a stronger connection with fBUT (r = 0.159) and MG secretion (r =  − 0.162) in the DE group and also had higher accuracy in diagnosing severe DE and borderline DE. In conclusion, the rear 4-min Schirmer test may be a supplement indicator in assessing tear secretion and diagnosing DE.

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.

Advances in Dry Eye Disease Examination Techniques

Dry eye-related ocular surface examination is very important in the diagnosis and treatment of dry eye disease. With the recent advances in science and technology, dry eye examination techniques have progressed rapidly, which has greatly improved dry eye diagnoses and treatment. However, clinically, confusion remains about which examination to choose, how to ensure the repeatability of the examination, and how to accurately interpret the examination results. In this review, we systematically evaluate previous examinations of dry eye, analyze the latest views and research hotspots, and provide a reference for the diagnosis and management of dry eye.

Assessment of tear film osmolarity using the IPen® Vet osmometer in Pug and Shih-Tzu dogs with and without keratoconjunctivitis sicca

OBJECTIVE

To establish tear film osmolarity (TFO) values in Pugs and Shih-Tzus, with and without keratoconjunctivitis sicca (KCS).

ANIMALS STUDIED

A total of 82 adult dogs were evaluated.

PROCEDURE

The inclusion criteria for the healthy group was a Schirmer tear test (STT-1) ≥15 mm/min with no clinical signs of KCS, whereas those with KCS had clinical signs and a STT-1 ≤10 mm/min. All animals underwent complete ophthalmological evaluation prior to STT-1 and TFO. Student's t tests were used to compare STT-1 and TFO in KCS and healthy eyes as well as possible differences in TFO between breeds. In addition, a linear regression to model the relationship between the two variables (STT-1 and TFO) was performed. A P-value ≤ 0.05 was considered statistically significant.

RESULTS

STT-1 results were significantly lower (p = 0.0001) in the KCS group (4.46 ± 1.74) compared with the control group (18.80 ± 2.02). Mean TFO results were significantly higher in the KCS group (353.02 ± 16.58 mOsm/L) (p < 0.0001) compared with the control group (315.27 ± 6.15 mOsm/L). The formula Y = 365.059-2.625 * X significantly predicts (p < 0.001) the value of the variable Y (TFO mOsm/L) as a function of the variable X (STT-1 mm/min), with a coefficient of determination of 0.71.

CONCLUSIONS

The results revealed differences in TFO and STT-1 between KCS and healthy dogs. Additionally, STT-1 and TFO values were correlated with the aim to use STT-1 values to predict TFO values in brachycephalic breeds.

Tear Film Surface Quality in Modern Daily Disposable Contact Lens Wear

OBJECTIVES

As reported previously, tear film surface quality (TFSQ) should be considered in contact lens (CL) fitting. This study followed noninvasive keratograph tear film break-up time (NIKBUT) in CL wearers for 12 months to validate its clinical utility in predicting CL performance.

METHODS

Fifty-five subjects (M/F=17/38) aged 26±4 years were prescribed silicone hydrogel or hydrogel CLs. The study included baseline measurements without CLs; 2 visits for CL fitting and control; follow-up after 3, 6, and 12 months of CL wear; and postwear visit without CLs. Ocular Surface Disease Index (OSDI), 8-Item Contact Lens Dry Eye Questionnaire (CLDEQ-8), first and mean NIKBUT (F/M-NIKBUT), fluorescein tear film break-up time (FBUT), and ocular surface staining were evaluated.

RESULTS

Post hoc analysis of each pair of visits showed differences between baseline and all CL visits for F-NIKBUT, M-NIKBUT, FBUT, and corneal staining. No difference was reported in symptoms. In addition, differences between baseline and postwear visits were noted in OSDI, M-NIKBUT, FBUT, and corneal staining, with three of the latter parameters showing a downward trend.

CONCLUSIONS

No changes in TFSQ and symptoms were reported over 12 months. Introducing NIKBUT as part of routine CL fitting is advised to improve CL fit and predict success.

Clinical comparison of tear film breakup time measurements in normal dogs using three different methods of fluorescein solution administration

OBJECTIVE

To evaluate whether the method of fluorescein administration affects the results of tear film breakup time (TFBUT) measurement in normal dogs.

ANIMALS STUDIED

Thirty-seven client and hospital staff owned dogs over 1 year of age with no known comorbidities or administration of systemic or topical ophthalmic medications.

PROCEDURES

A prospective randomized three-way crossover study was conducted. All dogs received an abbreviated ophthalmic examination to rule out ocular surface disease. Using a 30-min washout interval period, each dog's right eye was received: (a) direct application of fluorescein stain strip with one drop of sterile eyewash, (b) direct application of fluorescein stain strip with two drops of sterile eyewash, or (c) application of one drop from a premade fluorescein solution (dilution of one strip in 0.3 mL sterile eyewash). Eyes were assessed using the cobalt blue filter of a slit lamp biomicroscope. TFBUT measurements were summarized as means ± standard deviation. The methods were compared using mixed model analysis of variance. All analyses were performed using sas version 9.4.

RESULTS

Thirty-seven dogs met the inclusion criteria. Mean TFBUT ± standard deviation (SD) for the three described methods were: (a) 16.58s ± 6.9, (b) 15.98s ± 7.1, and (c) 16.43s ± 8.1. No differences between fluorescein stain application techniques were observed (p = .92).

CONCLUSION

The technique of fluorescein solution administration did not affect TFBUT measurement in this population of healthy dogs.

Reliability and efficacy of maximum fluorescein tear break-up time in diagnosing dry eye disease

This study aims to investigate the reliability and efficacy of maximum fluorescein tear break-up time (FTBUTmax) in diagnosing dry eye disease (DED). 147 participants were enrolled in this study. Ocular symptoms were assessed by Ocular Surface Disease Index (OSDI). The fluorescein tear break-up time (FTBUT) examination, corneal fluorescein staining (CFS), and Schirmer I test were performed on both eyes. Each participant underwent 3 consecutive FTBUT tests, and five types of FTBUT values including FTBUTmax, the minimum FTBUT (FTBUTmin), the first FTBUT (FTBUT1), the average of three FTBUTs (FTBUT123) and the average of the first and second FTBUT (FTBUT12) were recorded. FTBUTmax was larger than the other FTBUT values, but no differences were found among the values of FTBUT1, FTBUT123, FTBUT12 and FTBUTmin. In the ROC analysis, FTBUTmax had the largest or the second largest area under the ROC (AUROC) in all three DED diagnostic criteria, while FTBUTmin had the least AUROC of them. ROC efficacy of FTBUTmax was significantly higher than that of FTBUT123, FTBUT12, FTBUT1 and FTBUTmin in the OSDI criteria and higher than that of FTBUT1 and FTBUTmin in Schirmer I test and CFS tests. FTBUTmax has a close correlation with OSDI, Schirmer I test and CFS, and is an effective tool for the DED diagnosis.

Evaluation of Meibomian Glands in Obstructive Sleep Apnea-Hypopnea Syndrome

PURPOSE

To evaluate the effect of obstructive sleep apnea-hypopnea syndrome (OSAHS) on the meibomian glands, ocular surface, and tear parameters.

METHODS

The study included 59 individuals (32 subjects with OSAHS, 27 control subjects) who underwent polysomnography in the Chest Diseases Clinic. The right eyes of all individuals were evaluated in the Ophthalmology Clinic. The first noninvasive tear break-up time (f-NTBUT) and the average noninvasive tear break-up time were measured, and Schirmer test was applied. Meibography was taken (Sirius; CSO, Florence, Italy), and meiboscore was used for indexing meibography. Finally, a sample was taken for conjunctival impression cytology.

RESULTS

In the study and control groups, the median of f-NTBUT was 2.1 seconds [interquartile range (IQR); 1.5-5.0] and 5.7 seconds (IQR; 2.9-8.8) and the median of average noninvasive tear break-up time was 5.6 seconds (IQR; 3.6-9.5) and 7.2 seconds (IQR; 4.2-10.7), respectively (P = 0.007 and P = 0.487, respectively). The mean Schirmer value was 16.3 ± 5.9 mm (range; 5-25) and 17.3 ± 6.6 mm (range; 5-30) in the study and control groups (P = 0.604). In upper eyelid meibography, the median of loss in the meibomian glands was 20.10% (IQR; 11.60%-40.80%) in the study group and 14.70% (IQR; 10.40%-21.30%) in the control group (P = 0.043). In lower eyelid meibography, the median of loss in the meibomian glands was 19.00% (IQR; 13.60%-35.30%) in the study group and 12.40% (IQR; 9.10%-16.40%) in the control group (P = 0.002). The median of the Nelson grade in conjunctival impression cytology was 1 (IQR; 0-1) in the study group and 1 (IQR; 0-1) in the control group (P = 0.445).

CONCLUSIONS

The loss in the meibomian glands together with the shortened f-NTBUT shows that there could be a predisposition in OSAHS for evaporative dry eye originating from meibomian gland damage.

Subjective and Objective Evaluation of the Effect of Blink Type on Tear-film Breakup Time and Its Estimation

SIGNIFICANCE

While evaluating the tear-film breakup time, a careful set of precise instructions should be given to the subjects regarding the blink type because it substantially impacts the assessment of tear-film surface quality.

PURPOSE

The purpose of this study was to determine to what extent the type of blink affects the tear-film breakup time and its assessment using two types of videokeratoscopes and the fluorescein test.

METHODS

Thirty-three volunteers were assessed considering two different types of blinks: natural (short) and forced (unnaturally prolonged). Objective noninvasive breakup time estimation was performed using Oculus Keratograph 5M and Medmont E300, both equipped with tear-film analysis modules, followed by the fluorescein test. In addition, while overviewing videokeratoscopy recordings, noninvasive breakup time was assessed subjectively by one experienced observer marking the first noticeable distortion in the Placido-disk pattern. Statistical analyses included two-way ANOVA and paired-sample t test. The agreement between blinking and measuring modalities was assessed using Bland-Altman plots.

RESULTS

Forced blink significantly shortened the tear-film breakup time in all measuring modalities (two-way ANOVA, P = .003). The mean difference between breakup time after natural and forced blink was 3.2 (P = .002), 2.4 (P = .005), and 2.1 seconds (P = .002), for Keratograph 5M, E300, and fluorescein test, respectively. The group median of differences between objective and subjective noninvasive breakup time was less than 1 second with both videokeratoscopes. The objective noninvasive breakup time measured with Keratograph 5M was significantly longer than those with E300 and fluorescein test (both P < .001). No statistically significant difference was found between E300 objective assessment and fluorescein test (P = .19).

CONCLUSIONS

Forced blinks affect the assessment of tear-film stability. Hence, attention should be given in instructing the subjects before tear-film breakup time evaluation irrespectively to the method of measurement.

Efficacy and Safety of Phospholipid Nanoemulsion-Based Ocular Lubricant for the Management of Various Subtypes of Dry Eye Disease: A Phase IV, Multicenter Trial

Purpose

To evaluate the clinical efficacy and safety of propylene glycol/hydroxypropyl-guar (PG-HPG)-based nanoemulsion (Systane^® Complete) lubricant eye drops in participants with dry eye disease (DED).

Participants and Methods

In this phase IV, open-label, single-arm, interventional, multicenter study, adult participants with DED – subtyped into aqueous deficient, evaporative, and mixed dry eye – were instructed to instill one drop of PG-HPG in each eye twice a day for 28 days. Endpoints included change from baseline in tear film break-up time (TFBUT) (primary) and ocular discomfort visual analog scale (VAS) score at Day 14 and TFBUT at Day 28 (secondary). Safety was assessed throughout the study. Data were analyzed for overall patient cohort and by DED subtypes.

Results

A total of 134 participants received treatment (mean age: 56.6 years; female: 75.4%). At Day 14, the mean (standard deviation [SD]) TFBUT increased from 2.6 (1.00) seconds at baseline to 4.2 (2.92) seconds (mean change: 1.5 [2.80] seconds); median change was 0.8 seconds (95% CI: 0.52, 1.19) for the overall cohort; the change was maintained at Day 28 (mean change: 1.4 (2.80) seconds, median change: 0.8 seconds (95% CI: 0.49, 1.17). Subgroup analysis showed a mean change (SD) from baseline in TFBUT of 1.1 (2.41) seconds for aqueous deficient, 2.4 (3.17) seconds for evaporative, and 1.2 (2.63) seconds for mixed dry eye at Day 14, respectively. The ocular discomfort VAS score improved (decreased) from baseline at Day 14 (mean [SD] change: −17.3 [24.80]) for the overall cohort, −22.0 [21.73] for aqueous deficient, −17.6 [24.17] for evaporative and −13.1 [27.49] for mixed dry eye subgroups). Adverse events (AEs) were reported in 9 (6.7%) participants. No serious AEs were reported during the study.

Conclusion

Our study findings demonstrated that PG-HPG-based nanoemulsion lubricant eye drops were effective and well tolerated in participants with DED and all of its subtypes.

Effects of Oral Antihistamines on Tear Volume, Tear Stability, and Intraocular Pressure

The goal of this study was to investigate the effects of two commonly used oral antihistamines—diphenhydramine and loratadine—on tear volume, tear breakup time, and intraocular pressure. Placebo, diphenhydramine, and loratadine were administered for one week to 33 subjects experimentally blind to the treatment given. All the subjects received all three treatments over a period of six weeks. The outcome measures were the change in phenol red thread test (PRT), the tear breakup time (TBUT), and the intraocular pressure (IOP) of both eyes evaluated by experimentally masked observers. Neither of the mean changes in TBUT or IOP depended on the treatment given, but there was a significant monocular decrease in tear volume from diphenhydramine use. While we used an adequate treatment washout period of seven days, our investigation was limited by the short treatment times and inclusion of only young healthy patients. Overall, however, these results suggest that systemic diphenhydramine use should be limited to increase the effectiveness of conventional therapies. Clinicians should have fewer reservations about recommending the use of loratadine concurrent with dry eye treatments.

A Comparison of Efficacy and Safety of Two Lipid-Based Lubricant Eye Drops for the Management of Evaporative Dry Eye Disease

Purpose

The aim of this study was to compare the efficacy of two lipid-based lubricant eye drops in patients with lipid-deficient dry eye.

Methods

This Phase IV, multicenter, prospective, double-masked study enrolled adults (aged ≥18 years) who had a tear film breakup time (TFBUT) of ≤15 seconds(s), and unanesthetized Schirmer I test of ≥3 mm to ≤12 mm in at least one eye, at both screening and baseline visits. Eligible patients (n=231) were randomized (1:1) and received either Systane^® Balance (SYSB; n=117) or Refresh^® Optive Advanced (RFO-Ad, n=114), four-times a day, for 35 days. The primary endpoint was non-inferiority for change from baseline in TFBUT at Day 35 (non-inferiority was established if the lower limit of the 95% confidence interval (CI) for the difference between the treatment groups was > –1.0 s); secondary endpoints (test of superiority) were change in TFBUT and global ocular discomfort visual analog scale (VAS) score at Day 35. Other endpoints included the impact of dry eye on everyday life (IDEEL) treatment satisfaction scores (inconvenience and effectiveness) and safety.

Results

At Day 35, the mean change from baseline in TFBUT was 0.998 s in the SYSB and 0.868 s in the RFO-Ad groups with a treatment difference: 0.130 s; (95% CI −0.34, 0.60; P<0.0001) demonstrating non-inferiority of SYSB to RFO-Ad. The global ocular discomfort VAS scores improved in both groups, with a mean change from baseline of –9.7 and –8.8 in SYSB and RFO-Ad groups (treatment difference –0.8; P=0.62), respectively. No meaningful difference was observed in IDEEL treatment effectiveness and treatment inconvenience scores between SYSB vs RFO-Ad (P>0.05 for treatment difference). Both treatments were well tolerated.

Conclusion

SYSB lubricant eye drops were non-inferior to RFO-Ad for improvement in TFBUT in patients with lipid-deficient dry eye. Both lubricant eye drops improved TFBUT and ocular discomfort scores in patients with lipid-deficient dry eye.

Dynamics of Fluorescent Imaging for Rapid Tear Thinning

A previous mathematical model has successfully simulated the rapid tear thinning caused by glob (thicker lipid) in the lipid layer. It captured a fast spreading of polar lipid and a corresponding strong tangential flow in the aqueous layer. With the simulated strong tangential flow, we now extend the model by adding equations for conservation of solutes, for osmolarity and fluorescein, in order to study their dynamics. We then compare our computed results for the resulting intensity distribution with fluorescence experiments on the tear film. We conclude that in rapid thinning, the fluorescent intensity can linearly approximate the tear film thickness well, when the initial fluorescein concentration is small. Thus, a dilute fluorescein is recommended for visualizing the rapid tear thinning during fluorescent imaging.

Clinical subtypes of dry eye in youthful clinical sample in Ghana

PURPOSE

To evaluate in a cohort of patients with dry eye disease (DED) the distribution of patients with asymptomatic and symptomatic dry eye involving aqueous deficient or the evaporative subtype of DED.

METHODS

This was a clinic-based cross-sectional study of consecutive patients visiting the University of Cape Coast eye clinic for a comprehensive eye examination. Eligible participants completed the Ocular Surface Disease Index (OSDI), ocular surface staining and tear break up time. Subjects with dry eye (symptomatic or asymptomatic) underwent clinical examination comprising lid margin assessments, meibomian gland expressibility and quality assessments, and Schirmer 1 test.

RESULTS

A total of 172 patients were included in the study. The mean age of the eligible participants was 22.7 (±3.7) years, with a range of 17-35 years. There were 83 males and 89 females in the sample. There was an association between the form of the dry eye whether symptomatic or asymptomatic and sex, (X² = 6.51 df = 1 p = 0.011). The frequency of symptomatic aqueous-deficient dry eye was 9(5.2%) whiles that of the symptomatic evaporative dry eye was 20(11.6%). The frequencies of the asymptomatic aqueous-deficient dry eye and asymptomatic evaporative dry eye were 9(5.2%) and 12(7.0%) respectively. The frequency of symptomatic mixed dry eye was 30(17.4%) and the asymptomatic mixed dry eye was 8(4.7%). The distribution of unclassifiable dry eye among the symptomatic dry eye group was 41(23.8%) and 43(25%) among the asymptomatic dry eye group.

CONCLUSION

The number of patients exhibiting signs of the evaporative dry eye resulting from meibomian gland dysfunction far outnumbers those of aqueous deficient dry eye but there remains a high unclassifiable group with an unknown etiology. Further, studies are needed to explore the other etiology or etiologies of dry eye apart from meibomian gland dysfunction and reduced aqueous production.