-
Experimental Eye Research Oct 2017Meibum is a lipid-rich secretion that is produced by fully differentiated meibocytes in the holocrine Meibomian glands (MG) of humans and most mammals. The secretion is... (Review)
Review
Meibum is a lipid-rich secretion that is produced by fully differentiated meibocytes in the holocrine Meibomian glands (MG) of humans and most mammals. The secretion is a part of a defense mechanism that protects the ocular surface from hazardous environmental factors, and from desiccation. Meibomian lipids that have been identified in meibum are very diverse and unique in nature. The lipid composition of meibum is different from virtually any other lipid pool found in the human body. In fact, meibum is quite different from sebum, which is the closest secretion that is produced by anatomically, physiologically, and biochemically related sebaceous glands. However, meibum of mice have been shown to closely resemble that of humans, implying similar biosynthetic mechanisms in MG of both species. By analyzing available genomic, immunohistochemical, and lipidomic data, we have envisioned a unifying network of enzymatic reactions that are responsible for biosynthesis of meibum, which we call meibogenesis. Our current theory is based on an assumption that most of the biosynthetic reactions of meibogenesis are catalyzed by known enzymes. However, the main features that make meibum unique - the ratio of identified classes of lipids, the extreme length of its components, extensive ω-hydroxylation of fatty acids and alcohols, iso- and anteiso-branching of meibomian lipids (e.g. waxes), and the presence of rather unique complex lipids with several ester bonds - make it possible that either the activity of known enzymes is altered in MG, or some unknown enzymes contribute to the processes of meibogenesis, or both. Studies are in progress to elucidate meibogenesis on molecular level.
Topics: Bodily Secretions; Humans; Lipid Metabolism; Lipids; Meibomian Glands; Tears
PubMed: 28669846
DOI: 10.1016/j.exer.2017.06.020 -
Ocular Immunology and Inflammation May 2021: The meibomian glands are located in the tarsal plate of the upper and lower eyelid and are responsible for the production of a lipid-rich secretion, the meibum, which... (Review)
Review
: The meibomian glands are located in the tarsal plate of the upper and lower eyelid and are responsible for the production of a lipid-rich secretion, the meibum, which forms the outer component of the tear film. Meibomian gland dysfunction results in excessive evaporation of the tear film and is the leading cause of dry eye disease (DED). Despite the high prevalence of DED, the etiology of meibomian gland dysfunction is only basically understood. In addition, the molecular mechanisms of meibomian gland maturation and physiological function are currently the focus of research.: A systematic literature search was performed using the main scientific databases, including all relevant published articles up to September 2020.: This article provides an overview of the current state of knowledge about meibomian gland stem cells, cell surface marker expression and PPARγ signaling, as well as the pathological causes of meibomian gland dysfunction.: Androgen deficiency, hyperkeratinization, PPARγ signaling and inflammatory reactions including neutrophil extracellular traps (NETs) seem to be key factors within the pathological processes of the meibomian gland.
Topics: Dry Eye Syndromes; Humans; Inflammation; Meibomian Gland Dysfunction; Meibomian Glands; Tears
PubMed: 33945389
DOI: 10.1080/09273948.2021.1905856 -
Survey of Ophthalmology 2020Meibomian gland dysfunction is the leading cause of evaporative dry eye disease and is one of the most common conditions encountered by eye care providers. The disorder... (Review)
Review
Meibomian gland dysfunction is the leading cause of evaporative dry eye disease and is one of the most common conditions encountered by eye care providers. The disorder is characterized by obstruction of the meibomian gland terminal ducts and/or changes in their glandular secretion, resulting in changes in tear film stability, inflammation, and symptoms of irritation. There is no gold standard treatment for meibomian gland dysfunction, but rather a diversity of options. Conservative measures include warm compresses and lid hygiene, but there is growing interest and need for medical treatments and procedures. Potential medical treatments include antibiotics, nonsteroidal and steroidal anti-inflammatory agents, essential fatty acid supplementation, hormone therapy, and control of Demodex infestation. Procedures include intraductal meibomian gland probing, the use of electronic heating devices, intense pulsed light therapy, and intranasal neurostimulation. We provide an update on meibomian gland dysfunction treatments based on recent studies.
Topics: Disease Management; Humans; Meibomian Gland Dysfunction; Meibomian Glands; Tears
PubMed: 31494111
DOI: 10.1016/j.survophthal.2019.08.007 -
Eye & Contact Lens Jan 2018Meibomian gland dysfunction (MGD) is a leading cause of dry eye disease (DED). Meibomian gland dysfunction is divided into two major categories based on meibomian gland... (Review)
Review
Meibomian gland dysfunction (MGD) is a leading cause of dry eye disease (DED). Meibomian gland dysfunction is divided into two major categories based on meibomian gland secretion: low delivery and high delivery. The low-delivery states are further classified as either hyposecretory or obstructive subtype, and the high-delivery state is termed "hypersecretory MGD." Two parameters are commonly used to evaluate meibomian gland function: lipid layer thickness and meibum quality and expressibility. To evaluate the morphology of meibomian glands, meibography is used to detect meibomian gland dropout. Functional and morphological changes of meibomian glands are often thought to be well correlated; in reality, many cases do not because some patients have characteristics of both hypersecretory and obstructive subtypes. We suggest that the MGD classification system should be modified to include a mixed subtype to explain such patients.
Topics: Dry Eye Syndromes; Humans; Meibomian Glands; Tears
PubMed: 27755288
DOI: 10.1097/ICL.0000000000000336 -
The Ocular Surface Apr 2015The purpose of this review was to systematically analyze publications related to the role of meibomian gland disease in ocular surface inflammation, with special... (Review)
Review
The purpose of this review was to systematically analyze publications related to the role of meibomian gland disease in ocular surface inflammation, with special reference to meibomitis as an inflammatory form of meibomian gland dysfunction (MGD). Meibomian gland inflammation is often present with the ocular surface inflammation in conditions such as blepharokeratoconjunctivitis, ocular rosacea, and phlyctenular keratitis, but its contribution is often overlooked, especially in younger subjects. This can result in misdiagnosis, mistreatment, and, sometimes, severe visual impairment. We identified a related disease entity, seen predominantly in young patients, of ocular surface inflammation associated with meibomitis, which we termed meibomitis-related keratoconjunctivitis. Its specific clinical features are similar to those observed in the above-mentioned diseases, and the inflammatory form of MGD was found to be closely involved in the ocular surface inflammation seen in those four diseases, based on our statistical evaluation. The diagnosis and management of meibomitis, an inflammatory form of MGD, is vital for the successful treatment of the induced ocular surface inflammation. We propose that the ocular surface and the adnexal meibomian glands should be considered as one unit, i.e., the "meibomian gland and ocular surface" (MOS), when encountered in the clinical setting.
Topics: Blepharitis; Disease Management; Humans; Meibomian Glands
PubMed: 25881997
DOI: 10.1016/j.jtos.2014.12.002 -
The Ocular Surface Jul 2014This article compiles research regarding the neuroanatomy of the meibomian glands and their associated blood vessels. After a review of meibomian gland morphology and... (Review)
Review
This article compiles research regarding the neuroanatomy of the meibomian glands and their associated blood vessels. After a review of meibomian gland morphology and regulation via hormones, a case for innervation is made based on anatomical findings whereby the nerves lack a myelin sheath and Schwann cells. The localization and co-localization of dopamine beta-hydroxylase, tyrosine hydroxylase, neuropeptide Y, vasoactive intestinal polypeptide, calcitonin gene-related peptide, and substance P are explored with emphasis on differences that exist between species. The presence of the various neuropeptides/neurotransmitters adjacent to the meibomian gland versus the vasculature associated with the meibomian gland is documented so that conclusions can be made with regard to direct and indirect effects. Research regarding the presence of receptors and receptor proteins for these neuropeptides is documented. Evidence supporting the influence of certain neurotransmitters and/or neuropeptides on the meibomian gland is given based on research that correlates changes in meibomian gland morphology and/or tear film with changes in neurotransmitter and/or neuropeptide presence. Conclusions are drawn related to direct and indirect regulation and differences between the various nervous systems.
Topics: Animals; Humans; Meibomian Glands; Neurobiology; Neuropeptides
PubMed: 24999100
DOI: 10.1016/j.jtos.2014.01.005 -
Ophthalmology Nov 2017To discuss the pathology, causes, and ocular surface impact of meibomian gland disease (MGD), as well as its relationship to dry eye. (Review)
Review
TOPIC
To discuss the pathology, causes, and ocular surface impact of meibomian gland disease (MGD), as well as its relationship to dry eye.
CLINICAL RELEVANCE
MGD is a common disorder with various contributing mechanisms and clinical manifestations. Understanding MGD pathophysiology and its relationship to dry eye is important in order to optimize diagnosis and treatment algorithms.
METHODS
A review of current literature was performed to discern MGD in terms of pathophysiology, risk factors, and ocular surface impact, and the relationship to dry eye.
RESULTS
Meibomian gland obstruction and meibocyte depletion are important components of MGD. Many pathologies can disrupt function of meibomian glands, ranging from congenital to acquired causes. Once gland disruption occurs, the quality and quantity of meibum is altered, with a negative impact on the ocular surface. Increased tear evaporation, tear hyperosmolarity, increased ocular surface staining, increased inflammation, symptomatic irritation of the eyelid and globes, as well as decreased visual acuity have all been observed.
CONCLUSION
MGD leads to changes in meibum quality and quantity that can cause evaporative dry eye and ocular surface disruption, leading to dry eye symptoms in some individuals.
Topics: Animals; Dry Eye Syndromes; Eyelid Diseases; Humans; Meibomian Glands
PubMed: 29055358
DOI: 10.1016/j.ophtha.2017.05.031 -
Hong Kong Medical Journal = Xianggang... Feb 2019Dry eye disease is one of the most common ophthalmic complaints; it results from the activity of various pathways and is considered a multifactorial disease. An... (Review)
Review
Dry eye disease is one of the most common ophthalmic complaints; it results from the activity of various pathways and is considered a multifactorial disease. An important factor that contributes to the onset of dry eye disease is meibomian gland dysfunction. Meibomian gland dysfunction causes a disruption in the tear film lipid layer which affects the rate of tear evaporation. This evaporation leads to tear hyperosmolarity, eventually triggering the onset of dry eye disease. Dry eye disease and meibomian gland dysfunction are strongly associated with each other, such that many of their risk factors, signs, and symptoms overlap. This review aimed to provide an update on the association between dry eye disease and meibomian gland dysfunction. A stepwise approach for diagnosis and management is summarised.
Topics: Diagnostic Imaging; Dry Eye Syndromes; Eyelid Diseases; Fluorescent Dyes; Humans; Meibomian Glands; Randomized Controlled Trials as Topic; Risk Factors; Slit Lamp; Staining and Labeling; Tears
PubMed: 30713149
DOI: 10.12809/hkmj187331 -
Graefe's Archive For Clinical and... May 2021The aim of this study is to develop a new objective semiautomatic method for analysing Meibomian glands visibility quantitatively.
PURPOSE
The aim of this study is to develop a new objective semiautomatic method for analysing Meibomian glands visibility quantitatively.
METHODS
One hundred twelve healthy volunteers aged between 18 and 90 years (48.29 ± 27.46 years) participated in this study. Infrared meibography was obtained from the right upper eyelid through Oculus Keratograph 5 M. Meibographies were classified into 3 groups: Group 1 = patients with good subjective glands visibility and a gland dropout percentage < 1/3 of the total Meibomian gland area; Group 2 = patients with low subjective glands visibility and a gland dropout < 1/3; and Group 3 = patients with low subjective glands visibility and a gland dropout > 1/3. New metrics based on the visibility of the Meibomian glands were calculated and later compared between groups. Rho Spearman test was used to assess the correlation between each metric, and Meibomian gland dropout percentage with the entire sample and after excluding Group 2. A p value less than 0.05 was defined as statistically significant.
RESULTS
Fifty-six subjects were classified in Group 1 (24.48 ± 9.62 years), 19 in Group 2 (69.16 ± 21.30 years) and 37 in Group 3 (73.59 ± 13.70 years). No statistically significant differences were found between Groups 1 and 2 in dropout percentage. All metrics, with the exception of entropy, showed a higher Meibomian gland visibility in Group 1 than in the other two groups. Moderate correlations were statistically significant for all metrics with the exception of entropy. Correlations were higher after excluding Group 2.
CONCLUSION
The proposed method is able to assess Meibomian gland visibility in an objective and repeatable way, which might help clinicians enhance Meibomian gland dysfunction diagnosis and follow-up treatment.
Topics: Adolescent; Adult; Aged; Aged, 80 and over; Dry Eye Syndromes; Eyelid Diseases; Humans; Meibomian Glands; Middle Aged; Research Design; Tears; Young Adult
PubMed: 33409681
DOI: 10.1007/s00417-020-05034-7 -
Optometry and Vision Science : Official... Sep 2015The authors have reviewed the potential etiology and long-standing consequences of isotretinoin use in the development of dry eye symptoms in the absence of significant... (Review)
Review
The authors have reviewed the potential etiology and long-standing consequences of isotretinoin use in the development of dry eye symptoms in the absence of significant clinical findings. Despite the normal appearance of meibomian gland structure on meibography and minimal signs of eyelid margin inflammation, the secretory function of these glands is reduced and symptoms of dryness can greatly impact a patient's quality of life. The available literature indicates that isotretinoin's effect on the meibomian glands likely mimics its effects on the sebaceous glands of the skin in the treatment of acne. Several representative cases seen at the University of California Berkeley School of Optometry Dry Eye Clinic provide a clinical paradigm with the goal of raising awareness of the potential prevalence of this disease in patients who experience symptoms of dry eye. These cases highlight the importance of meibomian gland expression in determining whether there is poor quality and/or quantity of meibum secondary to reduced gland function. Currently, there is no definitive method to restore the structure and function of damaged meibomian glands; thus, treatment options for isotretinoin-associated meibomian gland dysfunction are primarily palliative to manage patient symptoms.
Topics: Animals; Dermatologic Agents; Dry Eye Syndromes; Eyelid Diseases; Humans; Isotretinoin; Meibomian Glands; Tears
PubMed: 26154692
DOI: 10.1097/OPX.0000000000000656