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The lid margin lines the palpebral fissure and joins the outside dry-oily skin with the inside aqueous-moist mucosa of the eye.
The lid margin lines the palpebral aperture and joins the dry skin with the moist conjunctival mucosa of the ocular surface.
The lid margin has different zones with different function. The smooth free lid margin constitutes the main surface towards the palpebral fissure. To each side it ends in a lid border.
The functions of the lid margin include
protection against environmental influences by the eyelashes as well as
the management of tears by the posterior lid border. It can acts both as a static dam and as a dynamic wiper for the spreading and stabilization of the eminently important tear film.
The integrity of the lid margin is a pre-requisite for the integrity of the ocular surface - and reverse (!)
The Lid Margin lines the palpebral aperture and joins the dry skin with the moist mucosa of the ocular surface
The free lid margin (arrows) lines the palpebral fissure and joins the outside dry-oily skin with the inside aqueous-moist mucosa of the eye.
The lid margin lines the palpebral aperture.
The change of the dry-oily skin to the aqueous-moist mucosa of the ocular surface occurs in the inner part at the posterior lid border - it divides the outside from the inside of the body. In another and probably more correct view, the lid margin can be described to join the outside skin to the inside mucosa of the conjunctiva, because both are continuous.
The lid margin had received less scientific attention in the past decades compared to the cornea and conjunctiva. In recent years several important links of the lid margin to ocular surface health and disease have been re-emphasized and thus the research on the lid margin has enjoyed a revival.
The lid margin is an essential working field of the Ocular Surface Center Berlin (OSCB) and members of the OSCB have contributed to major advancements in the knowledge of the structure, function and disease of the lid margin.
The lid margin has different zones with different function
The eyelid margin in the broader sense is the entire tissue lining the eyelid fissure - from the eyelid skin with the eyelashes to the eyeball.
In a narrower sense, however, one must distinguish between the actual "free" lid margin - which is only the smooth skin zone without hairs in the middle and its two lid 'borders'. Since the tissue structure is different in each case, these zones have a slightly different function and also different disorders and diseases.
In chronic inflammation of the eyelid margin (chronic blepharitis), for example, a distinction is therefore made between anterior and posterior blepharitis.
The meibomian oil glands open far back on the free lid margin (flm in the image), while the glands themselves are hidden inside the eyelid. The gland openings (open arrow in the image) form a regular line of small dots. Behind the gland openings lies the skin-mucosa transition zone (muco-cutaneous junction, mjc in the image), followed by the somewhat thickened epithelial cushion of the lid wiper (lw in the image) which rests on the eyeball. In this slit lamp photo, the lid margin is slightly everted from the eyeball and therefore the lid wiper becomes visible.
Outer Lid Border - the place of bacterial infection and Demodex hair mites
the outer or anterior lid border faces the outer skin of the eyelids
it contains the eye lashes (please see image), that are related to small glands similar to the other hairs of the body
this is the region where overshooting population of the eyelid with bacteria or overshooting infestation with Demodex hair mites can occur.
both is typically associated with deposits and incrustations on the lid margin. This is the rationale for the importance of regular lid hygiene and lidcare particularly when symptoms have already occurred.
Free Lid Margin - the location of Meibomian oil gland dysfunction and subsequent dry eyes
is a narrow smooth strip of epidermis facing the palpebral aperture
it contains the orifices of the Meibomian Glands (please see image), that are of utmost importance for ocular surface integrity as their dysfunction is the main causative factor for dry eye disease
depositions of oil and tear film material can build up on the free lid margin and contribute to inflammatory reactions
Inner Lid Border - alterations are related to Meibomian gland dysfunction and to tear film deficiency
the inner or posterior lid border follows towards the globe and has two sub-zones
the mucocutaneous junction (marked as mcj in the image), the epithelial transition zone between skin and mucosa. Its surface can be stained and constitutes the ´Line of MARX´ - this is the region where the meniscus of the tear film rests on, i.e. the bottom of the tear meniscus.
the mcj is followed by the elevated epithelial lip of the lid wiper (marked as lw in the image) that is in contact with the globe and serves for tear film distribution during the eyelid blink.
Some functions of the lid margin
Protection of the ocular surface against external influences is achieved by the anterior lid border
by the eye lashes that grow from the outer lid border in several rows
when the lids approach each other the lashes tend to constitute a meshwork that can act as a kind of filter against dust and the entrance of insects ... which is however of limited perfection.
Management of the tear fluid on the ocular surface is achieved by the posterior lid border
The Lid Margin can act as a "Static Dam" and as a "Dynamic Wiper"
The posterior lid border is in touch with the eye ball by the slightly thickened epithelial cushion that is termed the lid wiper. It separates the tear fluid in the palpebral fissure from the tears behind the eye lids.
The posterior lid border of the upper eye lid distributes the tears into the Tear FILM that is important for permanent moisture of the underlying tissue and for correct refraction which means perfect visual acuity.
Maintenance of the border between the dry skin and the moist ocular surface mucosa by integrity of the transition zone of the muco-cutaneous junction
The definition of the different lid margin zones will be considered in more detail in the Chapter "Overview on the Lid Margin".
The lid margin can act as a “Static Dam”
Concerning its static function as a dam, the lid margin is, in a way, “the outer end of the tear film”.
The lid margin normally prevents the tears from spillage out of the eye and over the outer lid skin. It thus helps to hold the tear film in place.
However, tear spillage (epiphora) with a ´watery eye´ can still occur, e.g.
either when the tear volume is too high. This may occur physiologically while crying or when the tear production is increased by reflex due to irritative stimuli, e.g. wind or foreign bodies. The high tear volume then exceeds the capacity of the lids as a “dam” … or
when the structure and shape of the lid margin ´dam´ is damaged. Deformations can occur from scarring or by a loss of elasticity and tension of the lid margin. The eyelid margin is then typically twisted to the inside (termed as entropion) or to the outside (termed as ectropion) and can no longer sufficiently hold the tears or serve for their drainage into the nose.
The lid margin can act as a “Dynamic Wiper”
The function of the lid margin as a "Dynamic Wiper" is necessary for the transformation of tear fluid on the eye into a very thin tear film.
This is the pre-requisite for intact refraction at the air-to-tear interface of the superficial Tear Film Lipid Layer (TFLL). It is the main surface of the eye for refraction with about three quarters of the refractive power of the eye and therefore indispensable for perfect visual acuity.
A perfect tear film is however only a necessary but not a sufficient condition for good vision. At the ocular surface also the underlying corneal surface must be reasonably smooth and with appropriate curvature to avoid higher order aberrations. They cannot be corrected by glasses but e.g. by a medical contact lens. This is discussed in the contact lens chapter in more detail.
Integrity of the Lid Margin is a Pre-Requisite for the Integrity of the Ocular Surface – and Reverse (!)
The lid margin is an essential structure in the maintenance of the pre-ocular tear film and of utmost importance for the functional anatomy of the ocular surface in order to preserve its integrity.
Morphological or functional disturbance of the lid margin as a whole, e.g. by inward or outward twisting (please see image) or of any individual zone such as the lid wiper in lid wiper epitheliopathy (LWE) is associated with dysfunction of the tear film and with subsequent Dry Eye Disease.
This is also true in return, as ocular surface alterations such as dry eye disease or simply contact lens wear can cause e.g. lid wiper epitheliopathy (LWE) of the posterior lid border.