Doctor's Forum > a) Why Comprehensive Treatment Today? + b) Tear Gland Physiology
c) pH and Gland Dysfunction + d) Optimizing Periocular Skin + e) Lid Hygiene. A Summary
f) Why Igiene Cleanser & Conditioner?+ g) Igiene C2 vs Baby Shampoo + h) Directions and Compliance

Keys: Micron thickness tear film, location all lipid-producing glands, dynamic structure.

‘THICKNESS’ OF THE LIPID LAYER

To appreciate the importance of lid hygiene, let us review the tear film characteristics.

The boundaries between the tear layers as well as their actual thickness are still under discussion, however it is generally accepted that the overall tear film is 7 micron thick (=0.0002756 inch), with 95% produced by the lacrimal glands, 3.5% is represented by the mucus layer and that the lipid layer ‘floats like oil on water’ as about 1/70th (or less than 1.5%) of this tiny total universe. The lipid layer is even further divided and consists of polar and non-polar lipids. The composition of the polar lipid is more complex than previously thought, but is probably only one to three molecules thick and serves as a surfactant between the aqueous tears and the thicker non-polar lipid layer. By way of illustration, the thickness of nearly 200 tear films (and 9000 lipid layers) would fit into the thickness of a single dime.

Clearly in this sub-micron universe, very little needs to deteriorate in the dynamic tear unit for a cascade of negative events. (Note: Conversely, very little needs to improve to have major benefits in eye health).

THE LOCATION AND TYPE OF LIPID GLANDS

The following data further underscore the importance of lid hygiene:

LGD instead of MGD. In every discussion of “Dry Eye”, the Meibomian Glands are mentioned, to the extent that it is questioned which came first: Dry Eye or Meibomian Gland Dysfunction. “Blepharitis” and MGD are often intertwined, even though the most common disease entity seen in a general ophthalmic practice is often secondary to a Meibomian dysfunction.

At Igiene Ophthalmic Labs, we propose that any advanced ophthalmic approach to Dry Eye embraces instead a new term: “LGD”. (LIPID GLAND DYSFUNCTION)

Not just one type, but multiple lipid glands. The narrow definition of “MGD” risks perpetuating a trivialization of the contribution to the overall lipid mix by the modified sebaceous glands of Zeiss and particularly the aprocrine glands of Moll, whose function, importance and performance in the overall lipid mix is not fully understood.

Natural antibiotic. While the Meibomian Glands are clearly critical in the main formation of the lipid layer, what is understood is that the glands of Moll point to a presence of the bacteriolytic enzyme lysomzyme, the membrane-associated mucin 1, and the immunoglobulin A and its secretory component within the gland suggest a function in local immune defense. It is further proposed that this aprocrine gland is active from birth in producing agents against pathogenic microorganisms in the eyelid shaft and on the ocular surface.

Location of lipid glands. All three glands that contribute to the lipid layer are located in the eyelids. The Meibomian glands are embedded within the tarsal plates (∽30-40 in upper lid and ∽20-30 in lower lid) arranged vertically and parallel to each other, with orifices open just in front of posterior edge of lid margin. The glands of Moll are aprocrine glands, secreting a milky viscous, probably merocrine secretion and opens in the cilia follicles by decapitation of apical cytoplasmic processes. They are more numerous in the lower lid. The glands of Zeiss are modified sebaceous glands attached directly to cilia follicles. They are unilobular with cells filled with frothy vacuolated cytoplasm due to myriad lipid drops. While not directly contributing to the tear film, eccrine glands commence slightly above lid margin within lid skin, found throughout all of lid skin up to the brow. Secretory portion lies at the basal coil located at the interface between lower reticular dermis and subcutaneous tissue. Cells empty by exocytosis.

Cascade of events in a dynamic structure. Approaching Dry Eye treatment from the LGD angle is also important, since the ocular surface, the tear, the lacrimal glands and the eyelids act as a functional unit to preserve the quality of the refractive surface of the eye and to resist injury. In this functional unit, the tear film is the most dynamic structure and its production and turnover is essential to maintaining the health of the ocular surface. Therefore a dysfunction of any tiny part of any of the layers can easily cascade in Dry Eye disease.

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