GLIMPSE on ...

The LID MARGIN

SUMMARY      (Every sentence here is LINKED to a respective CHAPTER below)

The LID MARGIN lines the palpebral aperture and divides the dry skin from the moist mucosa of the ocular surface. In another and more correct view, the lid margin can be described to JOIN the outside skin to the inside mucosa, because both are continuous and on the lid margin occurs the transition zone where the outside skin gradually transforms into the inside mucosa. This zone is termed the Muco-Cutaneous Junction (MCJ) - which is, however, not like a fence but it is a zone of gradual transition.  The Lid Margin has DIFFERENT ZONES with DIFFERENT FUNCTION -   an anterior rounded lid border with the eye lashes faces the outside whereas a sharp posterior lid border is apposed to the eye ball. In between these ´borders´  is the free lid margin without hairs but still covered by cornified skin epidermis. Some main FUNCTIONS for the lid margin reach from protection against environmental influences to the management of tears including 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 (!) because pathological alterations of the lid margin impair its function for wetting of the ocular surface and insufficient ocular surface wetting, in return, leads to wounding and alterations of the lid margin. Altogether this is a self-enforcing vicious circle for a deterioration of ocular surface moisture and tissue integrity ... that is leads to Dry Eye Disease. 

 

The Lid Margin lines the palpebral aperture and divides the dry skin from the moist mucosa of the ocular surface

The lid margin is the free margin of the eye lids and lines the palpebral aperture or fissure.  

The change of the dry skin to the moist mucosa of the ocular surface occurs on the Lid Margin and thus it divides the outside from the inside of the body.

In another an more correct view, the lid margin can be described to JOIN the outside skin to the inside mucosa, because both are continuous and on the lid margin occurs the transition zone where the outside skin gradually transforms into the inside mucosa. This zone is termed the muco-cutaneous junction (MCJ)- which is however not like a fence but a zone of gradual transition.

The lid margin had received less scientific attention in the past decades compared to the cornea and conjunctiva but 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 Lid Margin has different zones with a different epithelial structure and different function. The division of the zones is basically relatively easy: the free lid margin constitutes the main surface towards the palpebral fissure and to each side - anterior and posterior - it ends in a lid border. The anterior/outer lid border is towards the skin side whereas the inner/posterior lid border is towards the inside.   

  • OUTER LID BORDER with the eye lashes faces the outer skin of the lids
  • FREE LID MARGIN 
    • with the orifices of the MEIBOMIAN Glands,
    • they are physiologically still within the cornified epidermis and
    • Meibomian glands are of utmost importance for ocular surface integrity as their dysfunction is the main causative factor for dry eye disease
  • INNER LID BORDER 
    • the inner or posterior lid border start proximal to the end of the cornified skin epidermis and is probably the most important and interesting region because
    • it has the most diverse structure with two sub-zones and unction with the:
      •   the mucocutaneous junction (MCJ), an  epithelial transformation zone with the
      • ´Line of MARX´ as its surface and the tear meniscus overlying it, and
      • the elevated epithelial lip of the LID WIPER for tear film distribution 

 

Some MAIN FUNCTIONS of the Lid Margin

As the main Function of Lid Margin appears, apart from protection, the Management of the Tear FLUID and the  Maintenance of the Pre-Ocular  Tear FILM. (For didactic reasons the tear flow is exaggerated here because tear drops occur in the palpebral fissure only during increased lacrimation, e.g. in crying)

  • PROTECTION of the ocular surface against external influences is done  by the anterior lid margin
    • it is maintained through the eye lashes that grow from the outer lid margin in several  rows
    • when the lids almost approach each other the interacting meshwork of eye lashes constitutes 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 done by the posterior lid border
  • 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".

 

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 Zones is associated with dysfunction of the tear film and with subsequent Dry Eye Disease.