The Dry Eye Zone

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Abstract: MGs part III and IV

[Meibomian glands : part III. Dysfunction - argument for a discrete disease entity and as an important cause of dry eye]
Ophthalmologe. 2009 Nov;106(11):966-79.
[Article in German]
Knop E, Knop N, Brewitt H, Pleyer U, Rieck P, Seitz B, Schirra F.
Forschungslabor der Augenklinik, Charite - Universitätsmedizin Berlin, Campus Virchow Klinikum (CVK), Ziegelstrasse 5-9, 10117, Berlin, Deutschland.

Meibomian gland dysfunction (MGD), mainly synonymous with posterior blepharitis but typically without prominent inflammatory alterations of the lid margin, is a discrete disease entity and a frequent cause of wetting deficiencies of the ocular surface leading to dry eye disease that deserves increased recognition by clinicians. The history, classification, pathology, influencing factors, diagnostics and therapy are explained and discussed. MGD is mainly based on an obstructive mechanism caused by hyperkeratinization of the excretory duct and/or increased viscosity of the secretion (meibum) with subsequent deficiency of the tear film lipid layer. MGD is influenced by the hormonal status and by chemical and mechanical noxes as well as genetic defects and it occurs more frequently in women and generally increases with age. It results in stasis of meibum inside the glands, dilatation of the ductal system and eventually in atrophy and loss of glandular tissue (gland dropout). Careful investigation of the eyelids and lid margins with eversion, if necessary, should therefore be performed in every case of a wetting defect, notably before fitting contact lenses. Particularly important is the inspection of the meibomian orifices and diagnostic expression by mild mechanical compression of the lid.

[Meibomian glands : part IV. Functional interactions in the pathogenesis of meibomian gland dysfunction (MGD)]
Ophthalmologe. 2009 Nov;106(11):980-7.
[Article in German]
Knop E, Knop N.
Forschungslabor der Augenklinik, Charité - Universitätsmedizin Berlin, Campus Virchow Klinikum, Ziegelstrasse 5-9, 10117, Berlin, Deutschland.

Obstructive dysfunction of the meibomian glands (MGD) is surprisingly frequent in the general population and increases with age. Clinically, the focus is mainly on the consequences at the ocular surface in the sense of an evaporative dry eye syndrome. However, in addition, chronic obstruction of the meibomian glands also leads to degeneration of the secretory gland tissue which can result in a secondary hyposecretion even if the primary obstruction is later resolved by therapeutic approaches.Important influencing factors in the pathogenesis of obstructive MGDs and their interaction during the progression of the disease are systematically analyzed and displayed in a flow diagram. Age, hormonal disturbances and environmental influences, such as contact lenses, as well as qualitative alterations in the composition of the meibomian oil (meibum) lead to hyperkeratinization of the ductal epithelium and increased viscosity of the meibum which result, either alone or in combination, in obstruction of the duct and orifice. This leads to a lack of meibum on the lid margin and tear film with downstream hyperevaporative dry eye syndrome. At the same time, obstruction leads to a stasis of meibum inside the meibomian gland with increased pressure and resulting dilatation of the ducts and in atrophy of the acini with rarefaction of the secretory meibocytes and gland dropout. Stasis can also increase the growth of commensal bacteria, their production of oil degrading enzymes (lipases) and release of toxic mediators. These factors can, in return, act as self-enforcing feedback loops in the sense of vicious circles that aggravate the primary hyperkeratinization and compositional disturbance of meibum and can hence lead to a progressive MGD.