BackgroundPrevious lipidomic analyses of the human meibum had largely focused on individuals from non-Asian populations, despite the higher prevalence of dysfunctional tear syndrome (DTS) observed across Asia. Information pertaining to the alterations in lipid profiles in relation to DTS onset and progression is also lacking and warrants comprehensive experimental analysis.Methodologies/Principal FindingsWe examined the meibum lipidome of 27 DTS patients and 10 control subjects for a total of 256 lipid species from 12 major lipid classes, including cholesteryl ester (CE), wax ester (WE), triacylglyceride (TAG), (O-acyl)-ω-hydroxy fatty acid (OAHFA), glycerophospholipids (phosphatidylcholine, PC; phosphatidylethanolamine, PE; phosphatidylinositol, PI; phosphatidylglycerol, PG) and sphingolipids (sphingomyelin, SM; ceramide, Cer; glucosylceramide, GluCer; dihexosylceramide, DihexCer). Neutral lipids were analysed using high-performance liquid-chromatography coupled with mass spectrometry (HPLC/MS) and tandem mass spectrometry (MS/MS) was used for the qualitative and quantitative analysis of polar lipid species. DTS patients were classified into three severity groups (i.e. mild, moderate and severe) based on the ocular surface disease index (OSDI). A significantly lower level of TAG (p<0.05) was observed in patients under the moderate category compared to the mild category. Notably, a number of OAHFA species displayed consistently decreasing levels that correlate with increasing disease severity. An attempt was also made to investigate the changes in meibum lipid profiles of DTS patients compared to normal individuals classified based on OSDI score. Several unsaturated TAG and PC species were found at significantly higher levels (p<0.05) in patients than controls.ConclusionThe current study presents, for the first time, a comprehensive lipidome of meibum from individuals of an Asian ethnicity, which can potentially offer new insights into the higher prevalence of DTS observed amongst Asian populations. This study also represents an attempt towards identification of lipid species in meibum which could serve as marker for DTS.

Dry eye syndrome (DES) represents one of the most frequently encountered ocular morbidities, which can affect up to approximately one-third of the population worldwide depending on the criteria and defi nition used in the various studies conducted across the continents ( 1 ). Recent studies in China and Japan have, however, revealed a much higher prevalence than the average value reported globally ( 2, 3 ), indicating that Asian populations might have a greater predisposition to the disease. Despite its prevalence, there is presently no universal consensus on the diagnostic guidelines for the disease ( 4 ). Current clinical tests lack reproducibility and are not suffi ciently predictive of symptomatology to facilitate effective disease diagnosis and prognosis ( 5 ).The importance of tear lipids in maintaining ocular surface homeostasis and visual acuity due to their critical roles in constituting the outermost layer of the tear fi lm has been extensively reported and discussed ( 5-8 ). In particular, with the recent development in mass spectrometric technology, lipidomics has been transformed into a principal tool in biomedical research to decipher fi ne changes in lipid metabolism in various diseases including the DES ( 9, 10 ). Elucidating single tear components that are specifi cally altered with disease therefore marks the future of dry eye research by revealing novel molecular targets for improving current diagnostic and therapeutic platforms. Compared with tears, meibum-derived lipid markers indicative of DES Abstract As current diagnostic markers for dry eye syndrome (DES) are lacking in both sensitivity and specifi city, a pressing concern exists to develop activity markers that closely align with the principal axes of disease progression. In this study, a comprehensive lipidomic platform designated for analysis of the human tear lipidome was employed to characterize changes in tear lipid compositions from a cohort of 93 subjects of different clinical subgroups classifi ed based on the presence of dry eye symptoms and signs. Positive correlations were observed between the tear levels of cholesteryl sulfates and glycosphingolipids with physiological secretion of tears, which indicated the possible lacrimal (instead of meibomian) origin of these lipids. Notably, we found wax esters of low molecular masses and those containing saturated fatty acyl moieties were specifi cally reduced with disease and signifi cantly correlated with various DES clinical parameters such as ocular surface disease index, tear breakup time, and Schirmer's I test (i.e., both symptoms and signs). These structure-specifi c changes in tear components with DES could potentially serve as unifying indicators of disease symptoms and signs. In addition, the structurally-specifi c aberrations in tear lipids reported here were found in patients with or without aqueous deficiency, suggesting a common pathology for both DES subtypes.

ObjectivesTo estimate the cost and patterns of expenditure of dry eye treatment.MethodologyWe retrieved data on the type and cost of dry eye treatment in Singapore National Eye Centre from pharmacy and clinic inventory databases over a 2 year period (2008–2009) retrospectively. According to the type of treatment, data were sorted into 7 groups; meibomien gland disease (MGD) treatment, preservative free lubricant eye drops, preserved lubricant eye drops, lubricant ointments and gels, cyclosporine eye drops, oral supplements and non-pharmacological treatments/procedures. Each recorded entry was considered as one patient episode (PE). Comparisons in each group between two years were carried out using Pearson Chi-Square test. Significance level was set at alpha  = 0.05.ResultsCost data from 54,052 patients were available for analysis. Total number of recorded PEs was 132,758. Total annual expenditure on dry eye treatment for year 2008 and 2009 were US$1,509,372.20 and US$1,520,797.80 respectively. Total expenditure per PE in year 2008 and 2009 were US$22.11 and US$23.59 respectively. From 2008 to 2009, there was a 0.8% increase in total annual expenditure and 6.69% increase in expenditure per PE. Pharmacological treatment attributes to 99.2% of the total expenditure with lubricants accounting for 79.3% of the total pharmacological treatment expenditure. Total number of units purchased in preservative free lubricants, cyclosporine eye drops and MGD therapy have increased significantly (p<0.001) whereas number of units purchased in preserved lubricants and ointments/gels have reduced significantly (p<0.001) from 2008 to 2009.ConclusionDry Eye imposes a significant direct burden to health care expenditure even without considering indirect costs. Health care planners should be aware that these direct costs appear to increase over the time and more so for particular types of medications. Given the limitations of socio-economic data, true societal costs of Dry eye syndrome are likely to be much higher than estimated.

Migration of cells in the ocular surface underpins physiological wound healing as well as many human diseases. Transglutaminase (TG)-2 is a multifunctional cross-linking enzyme involved in the migration of skin fibroblasts and wound healing, however, its functional role in epithelial migration has not been evaluated. This study investigated the importance of TG-2 in a murine corneal wound healing model as well as the mechanistic role of TG-2 in the regulation of related biological processes such as cell adhesion and migration of cultured human corneal epithelial (HCE-T) cells. Corneal wound closure was delayed in homozygous TG-2 deleted mice compared to wild type mice. HCE-T cells that were knocked-down for TG-2 expression through stable expression of a short-hairpin (sh) RNA targeting TG-2, were delayed in closure of scratch wounds (48 compared to 12h in control cells expressing scrambled shRNA). TG-2 knockdown did not influence epithelial cell cycle progression or proliferation, rather, it led to reduced epithelial cell adhesion, spreading and velocity of migration. At the molecular level, TG-2 knockdown reduced phosphorylation of β-3 integrin at Tyr747, paxillin at Ser178, vinculin at Tyr822 and focal adhesion kinase at Tyr925 simultaneous with reduced activation of Rac and CDC42. Phosphorylation of paxillin at Ser178A has been shown to be indispensable for the migration of corneal epithelial cells (Kimura et al., 2008) [18]. TG-2 dependent β-3 integrin activation, serine-phosphorylation of paxillin, and Rac and CDC42 activation may thus play a key functional role in enhancing corneal epithelial cell adhesion and migration during wound healing.

Both lubricant eye drops, with or without HP-guar gelling agent, benefit patients in relieving dry eye symptoms. There was no difference in the efficacy of these drugs in terms of improving symptoms and altering objective signs of dry eye.