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Meibomian Gland Dysfunction: The MGDW Results
 

Meibomian gland dysfunction (MGD) may well be the leading cause of dry eye disease throughout the world. MGD is one of the major causes of evaporative dry eye and tear hyperosmolarity. Without a unified definition and classification system though, prevalence studies of MGD have varied widely but some have shown rates as high as 70%.1

MGD International Workshop Report: Definitions
The first global consensus report on meibomian gland dysfunction was published in a March 2011 special issue of the Investigative Ophthalmology & Visual Science (IOVS) journal. Like the 2007 DEWS (Dry Eye Workshop) report, The International Workshop on Meibomian Gland Dysfunction was conducted by the Tear Film & Ocular Surface Society (TFOS). The report is the result of findings from a two-year-long workshop composed of more than 50 leading clinical and basic research experts from around the world. Like the DEWS report, the Meibomian Gland Dysfunction Workshop report provides new evidence-based definitions of some common terms:2

  • Blepharitis: a general term that describes inflammation of the eyelid as a whole.
  • Anterior blepharitis: inflammation of the lid margin, anterior to the gray line.
  • Posterior blepharitis: inflammation posterior to the gray line. It is important to note that MGD is one of many potential causes of posterior blepharitis, and these terms should not be used interchangeably.
  • MGD: stands for meibomian gland dysfunction, not meibomian gland disease. The term dysfunction is used because the function of the meibomian glands is disturbed. Meibomian gland disease is used to describe a broader range of meibomian gland disorders, including neoplasia and congenital disease. Other terms such as meibomitis or meibomianitis describe a subset of disorders of MGD associated with inflammation of the meibomian glands.

MGD is newly defined in the MGDW report3 as:
A chronic, diffuse abnormality of the meibomian glands, commonly characterized by terminal duct obstruction and/or qualitative/quantitative changes in glandular secretion. It may result in alteration of the tear film, eye irritation, clinically apparent inflammation, and ocular surface disease.

As in the new definition of dry eye, this new definition of MGD also includes the term inflammation. MGD is further divided into two categories based on meibomian gland secretions: low-delivery and high-delivery states.3 Low delivery is the more common of the two and is further subdivided into hyposecretory and obstructive forms of MGD. Of these, obstructive non-cicatricial is the most common. High-delivery, hypersecretory MGD is characterized by the release of a large volume of lipid at the lid margin that becomes visible on application of pressure onto the tarsus during examination. Each MGD category also has primary causes, referring to conditions for which there are no discernible underlying causes or etiology.

Posterior Blepharitis
Recent literature has used the terms posterior blepharitis and MGD as if they were synonymous, but the MGDW found these terms to not be interchangeable. Posterior blepharitis describes inflammatory conditions of the posterior lid margin, of which MGD is only one possible cause. In its earliest stages, MGD may not be associated with clinical signs characteristic of posterior blepharitis. At this stage, affected individuals may be symptomatic, but alternatively, they may be asymptomatic and the condition regarded as subclinical. As MGD progresses, symptoms develop and lid margin signs, such as changes in meibum expressibility and quality and lid margin redness, may become more visible. At this point, an MGD-related posterior blepharitis is said to be present.

Meibomian gland dysfunction is caused primarily by terminal duct obstruction with thickened opaque meibum containing keratinized cell material. The obstruction, in turn, is due to hyperkeratinization of the ductal epithelium and increased meibum viscosity. The obstructive process is influenced by endogenous factors (age, sex, and hormonal disturbances) as well as by exogenous factors such as topical medication. The outcome of MGD is a reduced availability of meibum to the lid margin and tear film. The consequence of insufficient lipids may be increased evaporation, hyperosmolarity and instability of the tear film, increased bacterial growth on the lid margin, evaporative dry eye, and ocular surface inflammation and damage.

The consensus paper further proposes recommendations for diagnosing MGD and MGD-related disorders and presents a sequence of diagnostic tests to be performed in an order that will minimize the extent to which one test influences those that follow.

Also included in the report are recommendations for the evaluation and grading of the severity of MGD, management of and therapy for the disease and norms for clinical trials designed to evaluate pharmaceutical interventions for treatment.

Overall, MGD is an extremely important condition, conceivably underestimated, and very likely the most frequent cause of dry eye disease. While the breadth and depth of the consensus findings are expected to have a far-reaching impact on the clinical care of patients, the group of experts concur that additional research needs to be conducted to further study other aspects of MGD. These include its association with dry eye disease and standardized, validated ways to identify symptoms and signs of MGD.

REFERENCES
1. Jie Y, Xu L, Wu YY, Jonas JB. Prevalence of dry eye among adult Chinese in the Beijing Eye Study. Eye (Lond). 2009; 23: 688-693.
2. Nelson JD, Shimazaki J, Benitez-del-Castillo JM, et al. The International Workshop on Meibomian Gland Dysfunction: report of the definition and classification subcommittee. Invest Ophthalmol Vis Sci. 2011; 52: 1930-1937.
3. Nichols KK, Foulks GN, Bron AJ, et al. The international workshop on meibomian gland dysfunction: Executive summary. Invest Ophthalmol Vis Sci. 2011; 52 (4): 1922-1929.






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