The international workshop on meibomian gland dysfunction: report of the subcommittee on anatomy, physiology, and pathophysiology of the meibomian gland

Biophysical and morphological evaluation of human normal and dry eye meibum using hot stage polarized light microscopy

PURPOSE

To study melting characteristics and the morphology of human and mouse meibum.

METHODS

Hot stage cross-polarized light microscopy (HSPM) and immunohistochemical approaches were used.

RESULTS

Isolated human meibum, and meibum of mice (either isolated or within the meibomian ducts of mice), were found to be in liquid-crystal state at physiological temperatures. Melting of both types of meibum started at approximately 10°C and was completed at approximately 40°C. Melting curves of isolated meibum and meibum inside the meibomian ducts were multiphasic with at least two or three clearly defined phase transition temperatures, typically at approximately 12 ± 2°C (minor transition), 21 ± 3°C, and 32 ± 3°C, regardless the source of meibum. Melting was highly cooperative in nature. Samples of abnormal human meibum collected from dry eye patients with meibomian gland dysfunction often showed an increased presence of nonlipid, nonmelting, nonbirefringent, chloroform-insoluble inclusions of a protein nature. The inclusions were positively stained for cytokeratins. The presence of these inclusions was semiquantitatively characterized using a newly proposed 0 to 4 scale. In the presence of large amounts of these inclusions, melting characteristics of meibum and its structural integrity were altered.

CONCLUSIONS

HSPM is an effective tool that is suitable for biophysical and morphological evaluation of meibum. Morphological properties and melting characteristics of human meibum were found to be similar to those of mice. Abnormal meibum of many dry eye patients contained large quantities of nonlipid, protein-like inclusions, which were routinely absent in meibum of normal controls.

Effect of desiccating stress on mouse meibomian gland function

PURPOSE

Mice exposed to standardized desiccating environmental stress to induce dry eye-like symptoms have been used as a model to study the underlying mechanisms of evaporative dry eye. While studies have shown marked inflammatory and immune changes, the effect of such stress on meibomian gland function remains largely unknown. We sought to evaluate the effects of desiccating stress on meibocyte proliferation and meibum quality.

METHODS

Ten mice were treated with scopolamine and subjected to a drafty low humidity environment (30-35%). Five and ten days after treatment, eyelids were harvested and cryosections stained with Ki67 antibody to identify cycling cells. Sections were also imaged using stimulated Raman scattering (SRS) microscopy to characterize the gland compositional changes by detecting the vibrational signatures of methylene (lipid) and amide-I (protein).

RESULTS

Desiccating stress caused a 3-fold increase in basal acinar cell proliferation from 18.3 ± 11.1% in untreated mice to 64.4 ± 19.9% and 66.6 ± 13.4% after 5 and 10 days exposure, respectively (P < .001). In addition, SRS analysis showed a wider variation in the protein-to-lipid ratio throughout the gland, suggesting alterations in meibocyte differentiation and lipid synthesis.

CONCLUSIONS

These data are consistent with a model that a desiccating environment may have a direct effect on meibomian gland function, leading to a significant increase in basal acinar cell proliferation, abnormal meibocyte differentiation, and altered lipid production.

[Testosterone reduces the expression of keratinization-promoting genes in murine Meibomian glands]

BACKGROUND

Extensive keratinization appears to play a major role in the dysfunction of the Meibomian gland. This article presents the potential impact of androgens on limiting keratinization in this tissue, thus, contributing to normal Meibomian gland function and a healthy ocular surface.

MATERIALS AND METHODS

Orchidectomized mice were systemically treated with either testosterone or placebo for 2 weeks. The mRNA was then extracted from the Meibomian glands and differential gene expression was investigated by microarray hybridization and evaluation with GeneSifter software as well as gene ontology information from the Gene Ontology (GO) Consortium.

RESULTS

By z-score calculations, keratinization was the most significantly gene ontology term influenced by testosterone based on down-regulated genes in the mouse Meibomian gland. In particular, under the influence of testosterone the genes coding for small proline-rich protein (Sprr) 2a, Sprr 2b, Sprr 3, keratins 6a and 17 and periplakin were significantly down-regulated, while Sprr 1a and Sprr 2f were significantly up-regulated.

CONCLUSIONS

Testosterone down-regulates the expression of genes promoting keratinization in the Meibomian gland. This may help to prevent Meibomian gland dysfunction by limiting excessive keratinization of this tissue and the adjacent lid margins. The findings elucidate, at least in part, the beneficial impact of androgens on Meibomian gland function and thus on th e health of the ocular surface.

A randomized, double-masked study to evaluate the effect of omega-3 fatty acids supplementation in meibomian gland dysfunction

BACKGROUND

Dysfunction of the meibomian gland (MG) is among the most frequent causes of ophthalmological symptoms. The inflammation seen in meibomian gland dysfunction (MGD) is part of its pathogenesis, and evidence of the antioxidant-inflammatory properties of omega-3 fatty acids suggests this to be an appropriate treatment for MGD.

OBJECTIVE

We aimed to assess the effectiveness of omega-3 fatty acids versus placebo, in improving the symptoms and signs of MGD.

METHODS

We conducted a randomized and double-mask trial of 3 months duration. We enrolled 61 patients who presented with symptomatic MGD and no tear instability (defined as tear breakup time [TBUT] <10 seconds). Participants were randomly assigned to two homogeneous subgroups. For patients in group A, the study treatment included cleaning the lid margins with neutral baby shampoo and use of artificial tears without preservatives, plus a placebo oral agent. For patients in group B, the study treatment included cleaning the lid margins with neutral baby shampoo and use of artificial tears without preservatives, plus oral supplementation with omega-3 fatty acids. We performed the following tests: (1) TBUT; (2) Schirmer I test; (3) Ocular Surface Disease Index© (OSDI©; Allergan, Inc., Irvine, CA, USA); (4) MG expression; (5) evaluation of lid margin inflammation; and (6) interpalpebral and corneal dye staining.

RESULTS

After 3 months of evaluation, the mean OSDI, TBUT, lid margin inflammation, and MG expression presented improvement from the baseline values, in group B (P < 0.01, P < 0.001, P < 0.0001, P < 0.0001, respectively). The Schirmer test results were also improved and statistically significant (P < 0.01).

CONCLUSION

Oral omega-3 fatty acids, 1.5 grams per day, may be beneficial in the treatment of MGD, mainly by improving tear stability.

Meibography: A review of techniques and technologies

Meibomian glands play a significant role in tear production by contributing lipids to the superficial tear film.(1) Dysfunction of the meibomian glands destabilizes tears resulting in evaporative dry eye.(2,3) Historically, the meibomian glands were assessed in an ex vivo fashion through histologic studies. However, innovations in ocular imaging have advanced significantly in recent decades to include meibography. Meibography is an imaging study developed 35 years ago exclusively for the purpose of observing the morphology of meibomian glands in vivo.(4,5) In this review of meibography, we briefly describe the etiology of meibomian gland dysfunction and then discuss various meibography techniques, technologies, and methods of image analysis. We close with a review of the literature, crediting various studies for the significant contributions made toward our current understanding of the meibomian glands.

Tear film mucins: front line defenders of the ocular surface; comparison with airway and gastrointestinal tract mucins

The ocular surface including the cornea and conjunctiva and its overlying tear film are the first tissues of the eye to interact with the external environment. The tear film is complex containing multiple layers secreted by different glands and tissues. Each layer contains specific molecules and proteins that not only maintain the health of the cells on the ocular surface by providing nourishment and removal of waste products but also protect these cells from environment. A major protective mechanism that the corneal and conjunctival cells have developed is secretion of the innermost layer of the tear film, the mucous layer. Both the cornea and conjunctiva express membrane spanning mucins, whereas the conjunctiva also produces soluble mucins. The mucins present in the tear film serve to maintain the hydration of the ocular surface and to provide lubrication and anti-adhesive properties between the cells of the ocular surface and conjunctiva during the blink. A third function is to contribute to the epithelial barrier to prevent pathogens from binding to the ocular surface. This review will focus on the different types of mucins produced by the corneal and conjunctival epithelia. Also included in this review will be a presentation of the structure of mucins, regulation of mucin production, role of mucins in ocular surface diseases, and the differences in mucin production by the ocular surface, airways and gastrointestinal tract.

Tear film breakup and structure studied by simultaneous video recording of fluorescence and tear film lipid layer images

PURPOSE

The thinning of the precorneal tear film between blinks and tear film breakup can be logically analyzed into contributions from three components: evaporation, flow into the cornea, and tangential flow along the corneal surface. Whereas divergent tangential flow contributes to certain types of breakup, it has been argued that evaporation is the main cause of tear thinning and breakup. Because evaporation is controlled by the tear film lipid layer (TFLL) it should therefore be expected that patterns of breakup should match patterns in the TFLL, and this hypothesis is tested in this study.

METHODS

An optical system is described for simultaneous video imaging of fluorescein tear film breakup and the TFLL. Recordings were made from 85 subjects, including both with healthy and dry eyes. After instillation of 5 μL2% fluorescein, subjects were asked to blink 1 second after the start of the recording and try to maintain their eyes open for the recording length of 30 or 60 seconds.

RESULTS

Areas of tear film thinning and breakup usually matched corresponding features in the TFLL. Whereas thinning and breakup were often matched to thin lipid, surprisingly, the corresponding lipid region was not always thinner than the surrounding lipid. Occasionally, a thin lipid region caused a corresponding region of greater fluorescence (thicker aqueous layer), due to convergent tangential flow.

CONCLUSIONS

Areas of tear thinning and breakup can generally be matched to corresponding regions of the TFLL as would be expected if breakup is largely due to evaporation. Surprisingly, in some examples, the corresponding lipid area was not thinner and possibly thicker than the surrounding lipid. This indicates that the lipid was a poor barrier to evaporation, perhaps because of deficiency in composition and/or structure. For example, bacterial lipases may have broken down esters into component acids and alcohols, causing a defective TFLL structure with increased evaporation.

Four characteristics and a model of an effective tear film lipid layer (TFLL)

It is proposed that a normal, effective tear film lipid layer (TFLL) should have the following four characteristics: 1) high evaporation resistance to prevent water loss and consequent hyperosmolarity; 2) respreadability, so it will return to its original state after the compression-expansion cycle of the blink; 3) fluidity sufficient to avoid blocking secretion from meibomian glands; 4) gel-like and incompressible structure that can resist forces that may tend to disrupt it. These characteristics tend to be incompatible; for example, lipids that form good evaporation barriers tend to be disrupted by compression-expansion cycles. It is noted that clues about the function and organization of the TFLL can be obtained by comparison with other biological lipid layers, such as lung surfactant and the lipid evaporation barrier of the skin. In an attempt to satisfy the conflicting characteristics, a "multilamellar sandwich model" of the TFLL is proposed, having features in common with the skin evaporation barrier.

The influence of 13-cis retinoic acid on human meibomian gland epithelial cells

PURPOSE

Meibomian gland dysfunction (MGD) is a primary cause of dry eye disease. One of the risk factors for MGD is exposure to 13-cis retinoic acid (13-cis RA), a metabolite of vitamin A. However, the mechanism is not well understood. We hypothesize that 13-cis RA inhibits cell proliferation, promotes cell death, alters gene and protein expressions, and attenuates cell survival pathways in human meibomian gland epithelial cells.

METHODS

To test our hypotheses, immortalized human meibomian gland epithelial cells were cultured with or without 13-cis RA for varying doses and time. Cell proliferation, cell death, gene expression, and proteins involved in proliferation/survival and inflammation were evaluated.

RESULTS

We found that 13-cis RA inhibited cell proliferation, induced cell death, and significantly altered the expression of 6726 genes, including those involved in cell proliferation, cell death, differentiation, keratinization, and inflammation, in human meibomian gland epithelial cells. Further, 13-cis RA also reduced the phosphorylation of Akt and increased the generation of interleukin-1β and matrix metallopeptidase 9.

CONCLUSIONS

Exposure to 13-cis RA inhibits cell proliferation, increases cell death, alters gene expression, changes signaling pathways, and promotes inflammatory mediator and protease expression in meibomian gland epithelial cells. These effects may be responsible, at least in part, for the 13-cis RA-related induction of MGD.

In Vivo 3D Meibography of the Human Eyelid Using Real Time Imaging Fourier-Domain OCT

Recently, we reported obtaining tomograms of meibomian glands from healthy volunteers using commercial anterior segment optical coherence tomography (AS-OCT), which is widely employed in clinics for examination of the anterior segment. However, we could not create 3D images of the meibomian glands, because the commercial OCT does not have a 3D reconstruction function. In this study we report the creation of 3D images of the meibomian glands by reconstructing the tomograms of these glands using high speed Fourier-Domain OCT (FD-OCT) developed in our laboratory. This research was jointly undertaken at the Department of Ophthalmology, Seoul St. Mary's Hospital (Seoul, Korea) and the Advanced Photonics Research Institute of Gwangju Institute of Science and Technology (Gwangju, Korea) with two healthy volunteers and seven patients with meibomian gland dysfunction. A real time imaging FD-OCT system based on a high-speed wavelength swept laser was developed that had a spectral bandwidth of 100 nm at the 1310 nm center wavelength. The axial resolution was 5 µm and the lateral resolution was 13 µm in air. Using this device, the meibomian glands of nine subjects were examined. A series of tomograms from the upper eyelid measuring 5 mm (from left to right, B-scan) × 2 mm (from upper part to lower part, C-scan) were collected. Three-D images of the meibomian glands were then reconstructed using 3D “data visualization, analysis, and modeling software”. Established infrared meibography was also performed for comparison. The 3D images of healthy subjects clearly showed the meibomian glands, which looked similar to bunches of grapes. These results were consistent with previous infrared meibography results. The meibomian glands were parallel to each other, and the saccular acini were clearly visible. Here we report the successful production of 3D images of human meibomian glands by reconstructing tomograms of these glands with high speed FD-OCT.

Meibomian gland morphology in Japanese infants, children, and adults observed using a mobile pen-shaped infrared meibography device

PURPOSE

To compare meibomian gland morphology between children and adults.

DESIGN

Cross-sectional, observational case series.

METHODS

In an institutional setting, healthy pediatric (n = 78, 30 boys, 48 girls; mean age ± standard deviation, 4.1 ± 3.4 years; range 1 month - 12 years) and adult (n = 25, 11 men, 14 women; 31.3 ± 4.8 years; range 24-39 years) volunteers participated in the study. A noninvasive mobile pen-shaped infrared meibography device was used to observe the meibomian glands. Lost meibomian gland area (meiboscore) was scored from grade 0 (no meibomian gland loss) through grade 3 (>two-thirds of the total area lost). The number of meibomian glands in each eyelid was counted by reviewing the video. Eyelid width was measured using a ruler. Meibomian gland density was calculated as the number of meibomian glands divided by the eyelid width.

RESULTS

The numbers of meibomian glands in the upper/lower eyelids were 26.9 ± 3.9 / 22.0 ± 2.2 in the pediatric group and 28.1 ± 2.7 / 24.4 ± 2.6 in the adult group (P = .22, P < .0001). Eyelid width was 24.4 ± 2.4 mm in the pediatric group and 27.9 ± 1.57 mm in the adult group (P < .0001). Meibomian gland densities in the upper/lower eyelids were 1.09 ± 0.17 / 0.91 ± 0.11 in the pediatric group and 1.01 ± 0.12 / 0.88 ± 0.10 in the adult group (P = .03, P = .45).

CONCLUSIONS

The mobile pen-shaped infrared meibography device is useful for obtaining information on the meibomian gland structure, not only in adults but also in children, including infants. The morphology of the meibomian glands in children was the same as that in adults, distributing across the whole tarsal plates in both the upper and lower eyelids.

Insulin-like factor 3 promotes wound healing at the ocular surface

Tear fluid is known to contain many different hormones with relevance for ocular surface homeostasis. We studied the presence and functional role of insulin-like factor 3 (INSL3) and its cognate receptor RXFP2 (relaxin/insulin-like family peptide receptor 2) at the ocular surface and in tears. Expression of human INSL3 and RXFP2 was determined in tissues of the ocular surface and lacrimal apparatus; in human corneal (HCE), conjunctival (HCjE), and sebaceous (SC) epithelial cell lines; and in human tears by RT-PCR and ELISA. We investigated effects of human recombinant INSL3 (hrINSL3) on cell proliferation and cell migration and the influence of hrINSL3 on the expression of MMP2, -9, and -13 and TIMP1 and -2 was quantified by real-time PCR and ELISA in HCE, HCjE, and SC cells. We used a C57BL/6 mouse corneal defect model to elucidate the effect of topical application of hrINSL3 on corneal wound healing. INSL3 and RXFP2 transcripts and INSL3 protein were detected in all tissues and cell lines investigated. Significantly higher concentrations of INSL3 were detected in tears from male vs. female volunteers. Stimulation of HCE, HCjE, and SC with hrINSL3 significantly increased cell proliferation in HCjE and SC and migration of HCjE. Treatment with hrINSL3 for 24 hours regulated MMP2, TIMP1, and TIMP2 expression. The local application of hrINSL3 onto denuded corneal surface resulted in significantly accelerated corneal wound healing in mice. These findings suggest a novel and gender-specific role for INSL3 and cognate receptor RXFP2 signaling in ocular surface homeostasis and determined a novel role for hrINSL3 in corneal wound healing.

Diverse mediators modulate the chloride ion fluxes that drive lacrimal fluid production

PURPOSE

To learn whether locally expressed and systemic mediators might modulate the cholinergically induced transepithelial Cl(-) fluxes that underlie lacrimal fluid production.

METHODS

Reconstituted epithelial monolayers were exposed to a submaximal dose of the muscarinic agonist, carbachol (CCh), or to one of several paracrine mediators for 18 hours, then acutely stimulated with an optimal dose of CCh. Secretory Cl(-) fluxes were assessed as negative short-circuit currents (ISC).

RESULTS

Exposure to IL-6 at concentrations of 1 and 10 ng/mL and IL-1β at 10 ng/mL significantly decreased CCh-induced Cl(-) secretion. Prolactin decreased CCh-induced Cl(-) secretion, but the extent of the decrease diminished as the prolactin concentration increased from 20 to 200 ng/mL. CCh, 10 μM, prevented CCh, 100 μM, from eliciting Cl(-) secretion. Exposure to histamine, 10 mM, prevented formation of confluent monolayers. Exposure to histamine, 1 mM, decreased CCh-induced Cl(-) secretion, whereas exposure to 5-HT, 1 mM, potentiated CCh-induced Cl(-) secretion.

CONCLUSIONS

Chronic exposure to inflammatory cytokines may significantly impair cholinergically induced lacrimal fluid production. Concentrations of prolactin within the high range of normal values also may impair fluid production, but this effect is reversed at levels associated with pregnancy. Autonomic neurotransmitters and paracrine mediators that signal through different G protein-coupled receptors appear to exert varying influences, which range from complete suppression to potentiation of cholinergically induced fluid production. Thus, some hormones and paracrine mediators may impair secretion in apparently homeostatic glands as well as diseased glands, whereas mediators produced by certain immune cell infiltrates may actually enhance fluid formation.

Evaluation of the ocular tolerance of a novel eyelid-warming device used for meibomian gland dysfunction

PURPOSE

Obstructive meibomian gland dysfunction (MGD) frequently induces a chronic complaint with various symptoms related to dry eye and discomfort. Previous research indicates a pivotal role for heat therapy for melting the meibum as part of any successful management plan, but delivery of constant temperature during treatment is vital. This study evaluated the performance of a novel device designed to deliver controlled, latent, moist heat to the eyelids and surrounding area.

METHODS

The signs, symptoms and ocular temperature of 25 normal subjects (M8, F17; age 29.2±5.7 years) were recorded before and after a 10min application of the Blephasteam(®) device. Ocular temperature (non-invasive ocular thermography; A40 Flir, UK), tear film stability (NIBUT), intra-ocular pressure (IOP), and ocular surface staining and hyperaemia were recorded. Results were checked for normality and compared using paired t-tests.

RESULTS

Temperatures in both eyelids were significantly greater after device application (upper +1.7±0.9°C; lower +2.1±0.7°C, p<0.0005). Bulbar conjunctival hyperaemia significantly decreased after treatment (p<0.005), but limbal and palpebral hyperaemia remained similar (p=0.33 and p=0.11, respectively). Ocular surface staining (p=0.74) and tear film stability (p=0.12) were unchanged in this normal cohort, and there was no significant change in IOP (13.8±2.0mmHg vs 12.9±2.2mmHg; p=0.092).

CONCLUSIONS

The Blephasteam(®) device provides effective levels of warming that would be sufficient to melt meibum, and no adverse ocular responses were recorded in this cohort, indicating that this is a safe device. Interestingly, even in this normal cohort, ocular surface redness appears less after treatment.

Effect of growth factors on the proliferation and gene expression of human meibomian gland epithelial cells

PURPOSE

We hypothesize that growth factors, including epidermal growth factor (EGF) and bovine pituitary extract (BPE), induce proliferation, but not differentiation (e.g., lipid accumulation), of human meibomian gland epithelial cells. We also hypothesize that these actions involve a significant upregulation of genes linked to cell cycle processes, and a significant downregulation of genes associated with differentiation. Our objective was to test these hypotheses.

METHODS

Immortalized human meibomian gland and conjunctival epithelial cells were cultured for varying time periods in the presence or absence of EGF, BPE, EGF + BPE, or serum, followed by cell counting, neutral lipid staining, or RNA isolation for molecular biological procedures.

RESULTS

Our studies show that growth factors stimulate a significant, time-dependent proliferation of human meibomian gland epithelial cells. These effects are associated with a significant upregulation of genes linked to cell cycle, DNA replication, ribosomes, and translation, and a significant decrease in those related to cell differentiation, tissue development, lipid metabolic processes, and peroxisome proliferator-activated receptor signaling. Serum-induced differentiation, but not growth factor-related proliferation, elicits a pronounced lipid accumulation in human meibomian gland epithelial cells. This lipogenic response is unique, and is not duplicated by human conjunctival epithelial cells.

CONCLUSIONS

Our results demonstrate that EGF and BPE stimulate human meibomian gland epithelial cells to proliferate. Further, our findings show that action is associated with an upregulation of cell cycle and translation ontologies, and a downregulation of genetic pathways linked to differentiation and lipid biosynthesis.

A randomized double-masked study of 0.05% cyclosporine ophthalmic emulsion in the treatment of meibomian gland dysfunction

PURPOSE

To compare the efficacy of topical cyclosporine [0.05% cyclosporine A (CsA)] and preservative-free artificial tears in the treatment of meibomian gland dysfunction (MGD).

METHODS

A 3-month prospective, randomized, double-masked, parallel-group controlled trial enrolled 70 patients with symptomatic MGD and unstable tear film [tear breakup time (TBUT) <8 seconds]. Patients were randomized to topical CsA (0.05%; group A) and 0.5% carboxymethylcellulose (control; group B) instilled twice daily for 3 months. Ocular Surface Disease Index (OSDI), lid margin inflammation, meibomian gland expression, conjunctival injection, corneal and interpalpebral dye staining, noninvasive tear breakup time (NIBUT) using the Tearscope Plus and invasive fluorescein tear breakup time (FBUT), and Schirmer I test were performed.

RESULTS

At the 3-month evaluation, mean OSDI, NIBUT and FBUT, lid margin inflammation, meibomian gland expressibility, and tarsal injection showed significant improvement from baseline in group A (P<0.01, P<0.01, P<0.001, P<0.05, and P<0.001, respectively). In group B, only the OSDI improved significantly from baseline at 3 months (P=0.003). TBUTs (NIBUT and FBUT) were significantly longer in group A at all visits, and the mean change of TBUTs from baseline was also significantly greater in group A at 3 months (P<0.001).

CONCLUSIONS

Topical CsA 0.05% twice daily may be helpful in the treatment of MGD mainly by improving tear film stability.

Influence of aromatase absence on the gene expression and histology of the mouse meibomian gland

PURPOSE

We hypothesize that aromatase, an enzyme that controls estrogen biosynthesis, plays a major role in the sex-related differences of the meibomian gland. To begin to test this hypothesis, we examined the influence of aromatase absence, which completely eliminates estrogen production, on glandular gene expression and histology in male and female mice.

METHODS

Meibomian glands were obtained from adult, age-matched wild-type (WT) and aromatase knockout (ArKO) mice. Tissues were processed for histology or the isolation of total RNA, which was analyzed for differentially expressed mRNAs by using microarrays.

RESULTS

Our results show that aromatase significantly influences the expression of more than a thousand genes in the meibomian gland. The nature of this effect is primarily sex-dependent. In addition, the influence of aromatase on sex-related differences in gene expression is predominantly genotype-specific. However, many of the sex-related variations in biological process, molecular function, and cellular component ontologies, as well as in KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways, are remarkably similar between WT and ArKO mice. The loss of aromatase activity has no obvious effect on the histology of meibomian glands in male or female mice.

CONCLUSIONS

Our findings demonstrate that aromatase has a significant impact on gene expression in the meibomian gland. The nature of this influence is sex-dependent and genotype-specific; however, many of the sex-related variations in gene ontologies and KEGG pathways are similar between WT and ArKO mice. Consequently, it appears that aromatase, and by extension estrogen, do not play a major role in the sex-related differences of the mouse meibomian gland.

Increasing prevalence and severity of conjunctivochalasis with aging detected by anterior segment optical coherence tomography

PURPOSE

To evaluate the impact of aging on conjunctivochalasis in an objective manner using anterior segment optical coherence tomography.

DESIGN

Prospective clinical trial.

METHODS

Sixty eyes of 30 healthy volunteers (15 men, 15 women; age range, 24-75 years) without any ophthalmic diseases were recruited for the study. Subjects were organized into 3 sex-matched groups, each including 10 subjects according to their ages: 20-39 years (Group 1), 40-59 years (Group 2), 60-75 years (Group 3). Cross-sectional area of conjunctivochalasis was measured at 3 locations (temporal, central, and nasal) using Fourier-domain optical coherence tomography. Tear meniscus height was also measured in all images where a typical triangular-shaped tear meniscus was obtained.

RESULTS

In terms of the cross-sectional area of conjunctivochalasis, there were statistically significant differences among 3 groups at temporal and nasal locations (P < .001). At the central location, whereas there were no subjects in Groups 1 and 2, solely 3 eyes revealed conjunctivochalasis in Group 3. The severity of conjunctivochalasis affecting the temporal and nasal bulbar conjunctiva was strongly correlated with age (η(2) = 0.81, P < .001 and η(2) = 0.78, P < .001). Lower central tear meniscus height was compared among the groups and a significant increase with age was observed (P < .001).

CONCLUSION

Fourier-domain optical coherence tomography provides an objective and quantitative approach for assessing the stages of conjunctivochalasis. The current study objectively confirms that conjunctivochalasis can be observed even in younger, healthy eyes; its severity increases with age; and it may alter tear distribution along the lower lid.

Historical overview of imaging the meibomian glands

Growing knowledge of the role of the meibomian glands in dry eye disease and contact lens discomfort has resulted in a surge of interest in visualizing these glands within the eyelids. This manuscript provides an overview of the many different visualization methods that have evolved over the past 30–40 years. Some of the visualization methods covered in this review include lid transillumination, video and non-contact meibography, and imaging methods employing confocal microscopy, optical coherence tomography and ultrasound. This review has also highlighted all the studies to date that have employed meibography as part of their methods. An overview of the available meibography dropout grading systems will also be provided.

Eye

The Eye chapter of the 3rd edition of Haschek and Rousseaux’s Handbook of Toxicologic Pathology brings a comprehensive description of pathological processes affecting the ocular tissues in the most commonly used laboratory animals and their correlations with human diseases of interest in toxicology. Also presented are detailed descriptions of the structure and function of the different ocular tissues, the most advanced techniques applied in the toxicological evaluation of the eye, useful animal models of human disease, and known mechanisms of ocular toxicity. The introductory sections of the chapter also feature such essential topics as ocular embryology, an overview of clinical ophthalmic evaluation, and eye-specific techniques of tissue processing.

Minocycline controls clinical outcomes and inflammatory cytokines in moderate and severe meibomian gland dysfunction

PURPOSE

To assess clinical outcomes and tear cytokine levels in patients with moderate and severe meibomian gland dysfunction (MGD) after treatment with oral minocycline and artificial tears versus artificial tears only.

DESIGN

Prospective, randomized clinical trial.

METHODS

Sixty eyes of 60 patients with stage 3 or 4 meibomian gland dysfunction were enrolled. We evaluated the tear film break-up time, Schirmer test results, corneal and conjunctival fluorescein staining results, biomicroscopic examination results of lid margins and meibomian glands, and tear cytokine levels before and after 1 month and 2 months of oral minocycline and artificial tears (group 1) or artificial tears only (group 2). Tear samples were collected and analyzed using a BD Cytometric Bead Array (BD Bioscience, San Jose, California, USA) for detection of interleukin (IL)-1β, IL-6, IL-7, IL-8, IL-12p70, IL-17α, interferon-γ, tumor necrosis factor-α, and monocyte chemotactic protein-1. The Wilcoxon signed-rank test, Mann-Whitney U test, generalized linear model, and linear mixed model were performed.

RESULTS

Patients in group 1 showed statistically significant improvement in all clinical signs and symptoms after 1 month and 2 months of treatment. Patients of group 1 showed more significant improvement compared with those in group 2. Patients in group 1 also showed statistically significant reductions in IL-6, IL-1β, IL-17α, tumor necrosis factor-α, and IL-12p70 after 2 months of treatment.

CONCLUSIONS

Oral minocycline can provide clinical benefits in treating moderate and severe meibomian gland dysfunction by reducing inflammatory cytokine levels.

How to promote and preserve eyelid health

Disorders of the lacrimal functional unit are common in ophthalmological practice, with meibomian gland dysfunction, blepharitis, and dry eye forming a significant part of the general ophthalmologist’s practice. The eyelid and its associated structures form a complex organ designed to protect the fragile corneal surface and improve visual acuity. This organ is subject to a number of disorders, including meibomian gland dysfunction, dry eye syndrome, anterior blepharitis, allergic and dermatological conditions, and disorders associated with contact lens use. Although commonly described separately, disorders of the lacrimal function unit are better considered as a group of interacting pathologies that have inflammatory mediators as a central feature. Eyelid hygiene, in the sense of routine cleansing and massage of the eyelids, is well accepted in the management of many disorders of the eyelid. However, a broader concept of eyelid health may be appropriate, in which eyelid cleansing is but a part of a more complete program of care that includes screening and risk assessment, patient education, and coaching. The ophthalmologist has an important role to play in helping patients persist with routine eyelid care that may be long-term or lifelong. A number of preparations exist to make routine eyelid care both more effective and more pleasant, and might also improve compliance. Several such preparations have been devised, and are being assessed in clinical studies, and appear to be effective and preferred by patients over traditional soap and water or baby shampoo.

Characterization of ocular gland morphology and tear composition of pinnipeds

OBJECTIVE

The importance of tear film integrity to ocular health in terrestrial mammals is well established, however, in marine mammals, the role of the tear film in protection of the ocular surface is not known. In an effort to better understand the function of tears in maintaining health of the marine mammal eye surface, we examined ocular glands of the California sea lion and began to characterize the biochemical nature of the tear film of pinnipeds.

PROCEDURES

Glands dissected from California sea lion eyelids and adnexa were examined for gross morphology, sectioned for microscopic analysis, and stained with hematoxylin and eosin. The tear film was examined using interferometry. Tears were collected from humans and pinnipeds for the analysis of protein and carbohydrate content.

RESULTS

The sea lion has sebaceous glands in the lid, but these glands are different in size and orientation compared with typical meibomian glands of terrestrial mammals. Two other accessory ocular glands located dorsotemporally and medially appeared to be identical in morphology, with tubulo-acinar morphology. An outer lipid layer on the ocular surface of the sea lion was not detected using interferometry, consistent with the absence of typical meibomian glands. Similar to human tears, the tears of pinnipeds contain several proteins but the ratio of carbohydrate to protein was greater than that in human tears.

CONCLUSIONS

Our findings indicate that the ocular gland architecture and biochemical nature of the tear film of pinnipeds have evolved to adapt to the challenges of an aquatic environment.

The role of dyslipidemia on ocular surface, lacrimal and meibomian gland structure and function

PURPOSE

Dyslipidemia is characterized by high lipid blood levels that are risk factors for cardiovascular diseases, which are leading causes of death. However, it is unclear whether dyslipidemia is a cause of the dry eye syndrome (DES). Therefore we determined in transgenic mice models of dyslipidemia, whether there is an association with DES development.

METHODS

Dyslipidemic models included male and female adult mice overexpressing apolipoprotein CIII (Apo CIII), LDL receptor knockout (LDLR-KO) and ApoE knockout (ApoE-KO). They were compared with age- and gender-matched C57BL/6 mice. Ocular health was evaluated based on corneal slit lamp assessment, phenol red thread test (PRT) and impression cytology. Blood lipid profiles and histology of meibomian and lacrimal glands were also evaluated. Effects of high-fat diet and aging were observed in LDLR-KO and ApoCIII strains, respectively.

RESULTS

Body weight and lacrimal gland weight were significantly higher in male mice compared to females of the same strain (P < 0.05). Body weight was significantly lower in LDLRKO mice receiving high lipid diet compared to their controls (P = 0.0043). ApoE-KO were hypercholesterolemic and ApoCIII hypertriglyceridemic while LDLR-KO showed increases in both parameters. The PRT test was lower in male LDLR-KO mice with high-fat diet than control mice with standard diet (P = 0.0273). Aging did not affect lacrimal structural or functional parameters of ApoCIII strain.

CONCLUSIONS

DES development is not solely dependent on dyslipidemia in relevant mice models promoting this condition. On the other hand, lacrimal gland structure and function are differentially impacted by lipid profile changes in male and female mice. This dissociation suggests that other factors beside dyslipidemia impact on tear film dysfunction and DES development.

Aging and dry eye disease

Dry eye disease is a prevalent eye disorder that in particular affects the elderly population. One of the major causes of dry eye, meibomian gland dysfunction (MGD), shows increased prevalence with aging. MGD is caused by hyperkeratinization of the ductal epithelium of meibomian gland and reduced quantity and/or quality of meibum, the holocrine product that stabilizes and prevents the evaporation of the tear film. Of note, retinoids which are used in current anti-aging cosmetics may promote the development of MGD and dry eye disease. In this review, we will discuss the possible mechanisms of age-related MGD.

Androgen regulation of gene expression in human meibomian gland and conjunctival epithelial cells

PURPOSE

Androgens exert a significant influence on the structure, function and/or pathophysiology of the meibomian gland and conjunctiva. We sought to determine whether this hormone action involves the regulation of epithelial cell gene expression in these tissues.

METHODS

Immortalized human meibomian gland and conjunctival epithelial cells were treated with placebo or dihydrotestosterone (DHT) and processed for molecular biologic procedures. Gene expression was evaluated with BeadChips and data were analyzed with bioinformatic and statistical software.

RESULTS

Androgen treatment significantly influenced the expression of approximately 3,000 genes in immortalized human meibomian gland and conjunctival epithelial cells. The nature of DHT action on gene activity was predominantly cell-specific. Similarly, DHT exerted a significant, but primarily cell-specific, influence on many gene ontologies and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. These included groups of genes related, for example, to lipid dynamics, innate immunity, cell cycle, Janus kinase (JAK)-signal transducer and activator of transcription (stat) cascades, oxidative phosphorylation, the proteasome, and mammalian target of rapamycin (mTOR), Wnt, and peroxisome proliferator-activated receptor (PPAR) signaling.

CONCLUSIONS

Our findings support our hypothesis that androgens regulate gene expression in human meibomian gland and conjunctival epithelial cells. Our ongoing studies are designed to determine whether many of these genes are translated and play a role in the health and well being of the eye.

Neurotransmitter influence on human meibomian gland epithelial cells

PURPOSE

A striking characteristic of the human meibomian gland is its rich sensory, sympathetic, and parasympathetic innervation, yet the functional relevance of these nerve fibers remains unknown. Acting on the hypothesis that neurotransmitters are released in the vicinity of the gland, act on glandular receptors, and influence the production, secretion, and/or delivery of meibomian gland secretions to the ocular surface, the goal in this study was to begin to determine whether neurotransmitters influence the meibomian gland.

METHODS

Immortalized human meibomian gland epithelial (SLHMG) cells were examined for the presence of vasoactive intestinal peptide (VIP) and muscarinic acetylcholine (mACh) receptor transcripts and proteins. Cells were also exposed to VIP, carbachol, forskolin, and/or 3-isobutyl-1-methylxanthine (IBMX) to determine whether these agents, alone or in combination, modulate the adenylyl cyclase pathway, the accumulation of intracellular free calcium ([Ca2+]i), or cell proliferation.

RESULTS

Results demonstrate that SLHMG cells transcribe and translate VIP and mACh receptors; VIP, with either IBMX or forskolin, activates the adenylyl cyclase pathway, and the effect of VIP and forskolin together is synergistic; both VIP and carbachol increase intracellular [Ca2+] in SLHMG cells; and VIP with forskolin stimulates SLHMG cell proliferation.

CONCLUSIONS

This study shows that parasympathetic neurotransmitters and their agonists influence the function of human meibomian gland epithelial cells. It remains to be determined whether this action alters the production, secretion, and/or delivery of meibum to the ocular surface.

Barx2 and Fgf10 regulate ocular glands branching morphogenesis by controlling extracellular matrix remodeling

The lacrimal gland (LG) develops through branching morphogenesis and produces secretions, including tears, that lubricate and protect the ocular surface. Despite the prevalence of LG disorders such as dry eye, relatively little is known about the regulation of LG development. In this study, we show that the homeobox transcription factor Barx2 is highly expressed in conjunctival epithelium, eyelids and ocular [lacrimal, harderian (HG), and meibomian (MG)] glands and is necessary for normal ocular gland and eyelid development. Barx2(-/-) mice show defective LG morphogenesis, absence of the HG, and defects in MG and eyelid fusion. Ex vivo antisense assays confirm the requirement for Barx2 in LG bud elongation and branching. Gene expression profiles reveal decreased expression of several adhesion and matrix remodeling molecules in Barx2(-/-) LGs. In culture, Barx2 regulates expression of matrix metalloproteinases (MMPs) and epithelial cell migration through the extracellular matrix. Fibroblast growth factors are crucial regulators of LG development and we show that Barx2 is required for Fgf10-induced LG bud elongation and that both Barx2 and Fgf10 cooperate in the regulation of MMPs. Together, these data suggest a mechanism for the effects of loss of Barx2 on ocular gland development. Intriguingly, salivary glands that also express a high level of Barx2 develop normally in Barx2(-/-) mice and do not show altered levels of MMPs. Thus, the function of Barx2 is specific to ocular gland development. Based on our data, we propose a functional network involving Barx2, Fgf10 and MMPs that plays an essential role in regulating branching morphogenesis of the ocular glands.