Limbus Anatomy Flashcards
6 Limbus functions
1) anatomical transition zone
2) source of stem cells for corneal epithelium
3) nourishment to peripheral cornea- vascularity of limbus
4) immunosurveillance of ocular surface - source of immune cells - vascularity
5) anterior angle structures - pathways for aqueous outflow
6) site for surgical incision like in glaucoma
limbus boundaries
transition zone - between cornea and sclera, and cornea and conjunctiva
gadual 1.5 mm
pathologic limbus definition/borders
anterior border: line or plane connecting - termination of bowman’s layer and termination of descemet’s membrane
posterior border: line perpendicular to surface approx 1.5 mm posterio to first line (passing through scleral spur)
surgical limbus definition/borders
approximately 2 mm wide - when they make flap
viewed as anterior bluish gray zone - when cut partly thru sclera
gray color: gray trabecular meshwork beneath limbus stroma and appearing of filtration meshwork
cornea, blueish zone. scleral spur, sclera are important landmarks for surgical insicions
gross anatomical landmarks for limbus
corneolimbal junction
limboscleral junction
internal scleral sulcus
bordered by end of descemet’s membrane and scleral spur
sulcus is filled in by corneoscleral meshwork and canal of schlemm
external scleral sulcus
a slight groove on external surface of eyeball indicating line of union of sclera and cornea
filled in by conjunctiva
scleral spur
deep fibrils of sclera condense in a ring at limbus
anatomic landmark
scleral spur and circumcorneal annulus contribute to stability of corneal contour
trabecular meshwork tissue inserts into anterior scleral spur
ciliary body muscle takes origin in posterior scleral spur
histology of the limbus (superficial to deep)
conjunctiva tenon's capsule episclera corneascleral stroma or limbal stroma aqueous outflow structures
transition and changes at limbus
peripheral cornea blends with sclera
changes at limbus:
- epithelial layer thicker
- epithelium projects downward to connective tissue
- bowman’s layer and descemet’s layer end
- corneal stroma transtion into limbus with loss of transparency and orderly arrangement (collagen fibrils become larger and varied in diameter and arrangement, characteristic of sclera)
- conj. stroma, tenon’s capsule, episclera and limbal stroma begin
layers in limbus - conjunctiva
conjunctival epithelium:
non keritanized stratified squamous
-10-15 cell layers thick
-thickened epithelial layer
lacks goblet cells typically found in bulbar and fornix regions of conj.
-houses limbal stem cells
conjunctival stroma:
loose conn. tissue containing collagen fibrils and fibroblasts
-melanocyts, macorphages, mast cells, lymphocytes, plasma cells
-blood vessels
blood supply to conjunctiva at the limbus
conjuntival arterioles (supplied from episcleral arteries)
superficial marginal plexus branches into a) recurrent conjunctival arteries and b) peripheral corneal arcades
palisades of vogt
radial projections of fibrovascular tissues
radiate in spoke like fashion in cornea periphery
concentrated in superior and inferior limbus
contains nerves, blood vessels, and lymphatics
- superficial marginal plexus -> peripheral corneal arcades
- lympatic vessels run parallel to blood vessels in palisades
- specialized microenvironment
appear as thin grey projections
palisades contain thickned conj. epithelium site for limbal stem cells
layers in limbus - Tenon’s capsule
runs parallel to scleral
anterior: origin at limbus
posterior: merges with dural sheath of optic nerve
located b/n conj. stroma and episclera
-sandwiched b/n 2 vascular layers
dense connective tissue
avascular - noursished by conj. plexus and episcleral plexus
layers in limbus - episclera
thin layer of conn. tissue
superficial layer of sclera
collagen fibrils, fibroblasts, blood vessels
collagen fibers blend into scleral stroma
well-vascularized: branches of episcleral arteries and veins
originates at limbus and goes to ON
