It refers to a circumcorneal transitional zone of the conjunctivocorneal and corneoscleral junction.
It associated with two junction -
1- Conjunctivocorneal junction.
2- Corneoscleral junction.
*CONJUNCTIVOCORNEAL JUNCTION :-
°At this point, the bulbar conjunctiva is a tightly adherent to the underlying structures.
°The Substantia propria of the Conjunctiva stops here but it is epithelium continues with that of the cornea.
°The cells contains melanin and differ from those of the cornea in having no prickles between them.
°Limbal epithelium is similar to corneal epithelium but its basal cell are arranged in peculiar pattern called as pallisade of vogt, containing stem cells (these stem cells are unipotent stem cells).
*CORNEOSCLERAL :-
°It is the transition region between the Cornea and sclera.
°It is highly vascular.
°It is 1.5 mm width.
°It contains -
* Trabecular meshwork
*Canal of schlemm
°At this junction, the transparent corneal lamellae become continues with the oblique , circular and opaque fibres of the sclera.
SURGICAL LIMBUS :-
It is a 2 mm wide circumcorneal transitional zone between cleat cornea on one side and the opaque sclera on the other side.
Border of surgical Limbus :-
1- Anterior limbal border -
° it is the antr boundary of the surgical limbal seen form the exterior.
°Marked by Prominent ridge created by Insertion of the Conjunctiva and Tenon's capsule.
°The antr limbal border overlies the termination of the Bowman's membrane.
2- Mid limbal line -
°Junction of the blue zone with white area.
Overlies the termination of the Descemet's membrane.
°Most useful external landmark.
3- Posterior limbal border -
°It lies about 1 mm posterior to the mid Limbal line .
°It overlies the scleral spur and can only be seen with use of sclerotic scatter illumination.
°It forms the posterior border of the surgical Limbus.
Zones of surgical limbus :-
1- Blue Limbal zone -
°It is bluish translucent zone seen posterior to the antr limbal border.
°Adjacent to this bluish zone posterior is the white sclera.
°The extent of blue Limbal zone is about 1mm in superior quad , 0.8 mm in inferior quad and about 0.4 mm in nasal and temporal quad.
2- White Limbal zone -
°It is a 1 mm wide whitish area which lies between the mid-limbal line and the posterior limbal border.
°Overlies the the trabecular meshwork .
°The total width of the surgical limbus is greatest in the superior quad where width of blue zone is Max.
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