Overview on ...

The Eyelid MARGIN

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The eyelid margin delimits the interpalpebral fissure with the tar film

The edge of the eyelid - the eyelid margin - delimits the interpalpebral fissure between the eyelids through which light enters the eye for vision.  

The edge of the eyelid - the eyelid margin - (arrows in the figure) limits at the opening of the eyelids (the interpalpebral fissure) through which the light can enter the eye for vision.

The change from the oily-dry outer skin at the outside to the watery-moist membrane on the inside occurs on the eyelid margin. It separates the outside of the body from its inside.

The eyelid margin has attracted less scientific interest in recent decades than, for example, the cornea or the conjunctiva.

Currently, however, many important functions of the eyelid margin for health and disease of the ocular surface have been re-examined and investigated. Research on the eyelid margin has thus experienced a ´revival´ since about the turn of the millennium.

The eyelid margin is an essential work area for the Ocular Surface Center Berlin (OSCB) The members of the OSCB have made important contributions to advances in the understanding of the structure, function and diseases of the eyelid margin and its importance for the ocular surface.

 

The lid margin has different zones with different functions

The lid margin can be divided into different zones, each of which has a different structure and also a different function.

A rough outline of the lid margin relatively simple: In the middle is the 'free lid margin', that is limited to both the inside and outside, respectively, by a lid border.

The eyelid margin is seen here in clinical photos. The anterior border with the eyelashes (in figure A, the lid is slightly everted) is followed by the smooth strip of the free lid margin without hairs (figure on the right side, the lid is in normal position). The posterior border is rather sharp (open arrow in figure B, the lid is everted) and in normally in contact with the eyeball. The Meibomian glands are seen as whitish tissue streaks through the translucent tarsal conjunctiva (in figure B). The openings of the glands onto the lid margin are seen as a line of little dots close to the posterior lid border (indicated by an open arrow in figures A and B). They are seen in higher enlargement in a following figure.

  • The free lid margin of the eyelid is a smooth strip of tissue that is free of hairs. It extends along the middle of the lid margin from the eyelashes to the tear meniscus close to the eyeball.

    • Those who are more familiar with cosmetics may recognize the free margin as the area where a kajal eyeliner pen can favorably be applied - and those who have not known about this may get ideas what to try next ;-) However painting the free lid margin with a pen has the inherent risk to block the openings of the Meibomian glands that open onto the free lid margin close to the eyeball as can be inspected e.g. in a mirror.

  • At the relative round outer, anterior lid border the hairs of the eyelashes emerge in several rows from the depth of the keratinized skin, while

  • the quite sharp rear, posterior lid border partly consists of the conjunctival mucous membrane and ´distributes´ the tear film upon the eyelid blink.  

 

The free lid margin points towards the opened eyelid fissure. It is limited at the front by the roundish outer lid border (OLB) and behind by the rather sharp rear posterior lid border (PLB). The posterior border is in contact with the eyeball and acts as a lid wiper to create and maintain a thin but stable tear film. The openings (orifices) of the Meibomian glands onto the posterior lid margin are marked be an open arrow in the figure on the right side.

  • is the area between the end of the eyelashes at the front side backwards to the eyeball including the openings of the meibomian glands close to the eyeball

  • it is thus directed towards the palpebral fissure

  • the entire free margin is covered by keratinized epidermis

The epidermis continues from the outer hairy and keratinized eyelid skin over the roundish anterior lid border beyond eyelashes inwards. Although there are no more hairs ... the horny layer is still preserved. It extends over the entire free edge of the eyelid to the rear edge of the eyelid just behind the openings of the Meibomian glands.

  • integrates the Meibomian gland openings

    • that are still within the keratinized epidermis and thus

    • still belong to the free lid margin - which also corresponds to their embryological development

The Meibomian glands lie deep inside the tarsal plate of the posterior lamella of the eyelid. They are of utmost importance for the health of the ocular surface and for clear vision. Their most common dysfunction, Meibomian gland dysfunction (MGD), is also the most common cause of dry eye disease.

Anterior lid border

The outer, anterior lid border is more roundish compared to the relatively shart inner border

  • a main characteristic are the ciliary hairs of the eyelashes emerge

  • they typically constitute several rows and emerge from the depth of the keratinized skin

  • associated with the ciliary hairs are associate glands, the modified sweat glands of Zeiss and the sebaceous glands of Moll. They lie deep in the tissue and are thus not seen in clinical examination. The glands open into the hair follicle and their secretory products enter the surface of the lid margin via the opening of the hair follicle.

Posterior lid border

The back edge of the eyelid at the globe - the posterior lid border - is perhaps the most interesting region of the eyelid margin. This is where the greatest variety for structures and functions lies:

  • ( 1 ) the first outer part is the muco-cutaneous junction between oily skin and dry mucous membrane

  • ( 2 ) the second inner part is in touch with the globe and constitutes the lid wiper.

( 1 ) The LINE of MARX is the skin-mucous membrane border and the floor of the tear meniscus

The TEAR MENISCUS (blue arrows in all schematic drawings) is the clearly thickened ´END´ of the tear film where it touches the eyelid margin. The formation of the tear meniscus (´tear lake´), which contains more tear fluid than the tear film itself and is roughly triangular in cross-section (fig. Left), is related to the surface tension. In high magnification (excerpts on the far right) one can see that the tear meniscus lies on the MARX line (red-brown arrows, far left), which in turn is the surface of the skin-mucous membrane boundary (MCJ) - this is the anterior, first Zone of the posterior edge of the lid. The second, posterior, zone of the lid touches the eyeball / globe - there the marginal conjunctiva forms the thickened epithelial lip of the lid wiper, which pulls out the tears into a very thin tear film.

After the end of the epidermis, the mucous membrane-skin transition zone, the so-called muco-cutaneous junction, mostly abbreviated as MCJ .

  • At the beginning of the MCJ there is the border between the dry-oily skin and the watery-moist mucous membrane

  • This epithelium is incompletely cornified (para-keratinized) and already moist

  • The surface of the MCJ (the parakeratinized epithelium)

    • is the ´floor / pad´ of the tear meniscus

  • and at the same time corresponds to the ´line of MARX´

The LINE OF MARX a narrow tissue streak that can naturally be stained with some vital dyes that the clinician uses for diagnosis - while the entire rest of the surface of the eye does not naturally take up any stains ! The line of Marx runs almost all along the inner lid border of both the lower and upper eyelids with exception of the most nasal part

( 2 ) the ´ marginal conjunctiva ´ forms the lid wiper to spread the tear film

The inner part of the posterior lid border is in contact with the globe (figure A) and is termed as the ´lid wiper´ because it wipes over cornea and distributes the tears into the tear film. Histologic investigations have shown that the epithelium forms a slightly elevated epithelial lip (figure B) similar to a windscreen wiper (figure C). The lid wiper is thus ideally suited for spreading a very thin tear film. (here is a respective publication)

On the epithelial surface, the MCJ shows a smooth transition into the marginal conjunctiva

  • the transition is exactly at the highest point of the posterior lid border

  • the beginning of this zone is formed by a thickened epithelial cushion - an epithelial lip, which is also known as the lid wiper

  • The designation ´Lid Wiper´ is based on the fact that this is the region of the eyelid that actually wipes over the eyeball during an eyelid blink and thereby spreads the tear fluid from the tear meniscus into the very thin but reasonably stable tear film.

  • This is essential for


The lid wiper has a built-in humidification system made of goblet cells

The raised epithelial lip of the lid wiper is that part of the eyelid that is in contact with the globe. The rest of the tarsal conjunctiva is separated from the eyeball by the narrow tear lake of "Kessing's Space" ( please see image) .

During the downward movement of the upper eyelid, the lid wiper compresses the ´old´ tear film, which often shows thin areas or disturbances. With the upward movement of the upper eyelid, the lid wiper distributes a new tear film ( see animation below ). 

Since the raised epithelial lip of the lid wiper is the essential part of the eyelid that rests on the globe, the mechanical frictional forces are concentrated in a relatively small area during the eyelid blink.

In order to compensate for the mechanical friction, the eyelid wiper has, so to speak, a 'built-in lubrication system' made of slime-forming goblet cells, as members of our scientific group were able to show.

If there is increased friction on the surface of the eye, the lid wiper is damaged

However, if conditions with increased friction occur at the surface of the eye, e.g. with dry eyes or when wearing contact lenses, the natural ´integrated´ lubrication capacity of the lid wiper is no longer sufficient and the tissue can be damaged.

The lid wiper is therefore the zone in which the first and most damage occurs when there is increased friction. It could be shown that the pathological vital staining of such epithelial damage of the lid wiper (termed as Lid Wiper Epitheliopathy, LWE ) is the most sensitive marker for conditions with increased mechanical friction on the surface of the eye.

=> Here you can find more information about the clinically important Lid Wiper Epitheliopathy .

The main function of the LID EDGE, apart from a protective function, is the MANAGEMENT of the tear fluid on the eye and its transformation into a tear film. (The flow of tears in this schematic representation is increased compared to normal and corresponds approximately to that when crying)

  • PROTECTION of the surface of the eye against external influences is provided by the anterior lid margin

    • through the eyelashes that grow in several rows over the outer edge of the eyelid

    • When the upper and lower eyelids approach each other, the crossing rows of lashes on both lids form a kind of grid against dust and insects ... which is only of limited perfection.

  • TEAR FLUID MANAGEMENT on the surface of the eye is carried out from the rear edge of the eyelid, where it is in contact with the eyeball

  • Maintenance of the normal SKIN-MUCCOAL BORDER

    • between the oily-dry skin and the watery-moist mucous membrane

    • due to the intactness of the skin-mucous membrane transition zone (MCJ)

The integrity of the eyelid margin is a pre-requisite for the health of the surface of the eye - and vice versa (!)

The edge of the eyelid is of enormous importance for the maintenance of the tear film in front of the eye and therefore also of enormous importance for the intact functional anatomy and health of the ocular surface. 

The entire surface of the eye is an integrated functional system ... in which all parts have to function in order to maintain overall health and thus clear vision. Disturbances of the edge of the eyelid, especially in the area of ​​the rear edge of the eyelid, can significantly disrupt the stability of the tear film, as (1) it can only be made thin and even by the lid wiper of the rear edge of the eyelid and (2) the tear film on the rear edge of the eyelid as Base rests. Dry eye can be a typical consequence of disorders of the lid edge.

Disturbances in the structure of the eyelid margin and its different zones can continue in disturbances of the tear film and thus ultimately ´ scratch ´ at the functional basis of the surface of the eye , which we got to know in the chapter about the " surface of the eye " ... and this can then typically lead to The development of the prototypical disease of the surface of the eye lead to ... the DRY EYE   !

The entire surface of the eye is therefore an integrated functional system , which for its intact health depends on the health of its individual components - functional disorders can therefore only be tolerated to a certain extent and then lead to disease symptoms.