Etty Bitton, BSc, OD, MSc is an Associate Professor at the École d’optométrie, Université de Montréal, and Director of its Clinical Externship Program. Her research interests include tear film evaluation, dry eye and contact lens wear.Dry eye is one of the most common complaints of patients consulting with eye care practitioners. Common contributing factors include contact lens wear, environmental effects such as dry climates, and allergies. Concomitant lid pathologies have also been identified as important contributing factors to dry eye, including lid margin bacterial infections, called blepharitis. Blepharitis can be divided into two types, notably anterior blepharitis which can be observed as a yellow crusting or “collarettes” at the base of the eyelashes coupled with redness of the lid margin. Posterior blepharitis, also known as Meibomian Gland Dysfunction (MGD), affects the posterior part of the lid margin, affecting the meibomian glands and their lipid-based secretions. The lipids assist in maintaining the stability of the ocular tear film by retarding the evaporation of the underlying water-based tears. An increase in research on blepharitis has improved our collective understanding of the disease and its effect on the ocular surface. The following summarises a 2010 article that provides a detailed overview of what has been learned about the meibomian glands and their influence on dry eye, the latest technology in the evaluation of meibomian secretions (meibum), as well as the newest therapies for MGD.
Foulks GN, Borchman D. Meibomian gland dysfunction: The past, present and future. Eye & Contact Lens 2010;36(5):249-253.
Meibomian glands and MGD
The meibomian glands, which are modified sebaceous glands, have a hyperplastic epithelium that can keratinize, obstructing the flow of meibum. Inflammation, which occurs when free fatty acids and triglycerides are released, has been found to respond to treatment with antibiotics (tetracycline class), which reduces these lipid components. Although no conclusive evidence is available for the prevalence of MGD, best estimates range from 37-50% of patients having the problem. The secretion of the glands, termed meibum, is altered with age and disease.
The composition of meibum
Meibum composition is controversial and highly dependent on the analytical technique used. That being said, meibum collected from patients suffering from MGD has been reported to contain:
– higher levels of phosphatidylcholine, phospholipid unsaturation and wax esters;
– lower levels of phosphatidylethanolamine, sphingomyelin, cholesterol and triglycerides.
Discrepancies in the literature are related to methodologies of extraction and evaluation.
Meibum from patients with MGD contain more protein and fewer double bonds, cholesterol esters and CH3 groups than secretions from normal subjects. Compositional differences in meibum render it more viscous, making it difficult to secrete onto the lid margin with blinking. These characteristics are apparent with the use of infrared spectroscopy and Principal Component Analysis (PCA), both powerful diagnostic tools that can discriminate between abnormal and normal meibomian gland secretions.
Meibography is a technique whereby a transilluminator (penlight) is placed on the back of an everted lid, enabling assessment of the number and linearity of the meibomian glands. Using meibography, a loss of glands, or gland dropout, has been shown to increase with age, especially after the age of 30 years. The opacity of the meibum and overall tear film osmolarity also increase with age.
Treatment of MGD
Increased knowledge of blepharitis and its separation into anterior and posterior components allows for a more targeted therapeutic approach.
While therapy for anterior blepharitis includes antibiotic treatment to reduce the bacterial load coupled with an anti-inflammatory, dependent on the severity and involvement of the lid margin, therapies for posterior blepharitis (MGD) have traditionally been limited to warm compresses and lid massage, to soften the meibum and improve lipid-based secretions.
Antibiotics have also shown limited promise in the treatment of MGD:
– Topical cyclosporine can improve lid margin inflammation but has little to no effect on meibum quality.
– Topical azithromycin has been reported to be successful in reducing both the clinical signs and symptoms of MGD.
– Oral tetracycline therapy has shown improvement in treating MGD but requires time (usually several months) and can be poorly tolerated by patients, limiting its success.
Omega-3 fatty acids have been cited as an effective therapy for MGD, but little evidence-based science is available to support this claim.
MGD and the future
Since the 2010 article was published, an international board of experts on the subject has focused on providing a uniform definition and classification of MGD (International Workshop on MGD), published as a special issue of Investigative Ophthalmology & Visual Science (March 2011). This resource will provide a standard platform that the international scientific community can use as a reference on MGD.
