Ocular Anatomy 5 Cornea Flashcards
(31 cards)
When does corneal development begin
33 days of gestation after the lens cup separates from the surface ectoderm
What is corneal epithelium derived from? Endothelium? Fibroblasts that produce corneal stroma?
Epithelium - surface ectoderm
Endothelium and fibroblasts stroma - neural crest cells
What determines the final diameter of the cornea
The optic cup diameter
Describe development of the cornea
- Production of a bilayered epithelium and basement membrane separate from the bilayer of endothelial cells and associated basement membrane
At 7 weeks, primitive stroma is formed, infiltrated by fibroblasts which produce collage fibrils
When is descemet’s membrane formed?
3 months gestation
When are corneal nerves formed
By 5 month
When is the corneal fully formed
7 months
What are the average dimensions of the cornea?
Horizontal diameter 11.7mm
Vertical diameter 10.6mm
What is the radius of curvature of the anterior and posterior surface of the cornea
Anterior 7.8mm
Posterior 6.5mm
What is the thickness of the cornea at the limbus and centrally
Limbus 1.1mm
Centrally 0.5mm
What is the refractive index of the cornea
1.36
What meridian is the cornea more curved
Vertical
What are the layers of the cornea?
Epithelium
Bowman’s membrane
Stroma (substantia propria)
Descemet’s membrane
Endothelium
What epithelium does the cornea have
Stratified squamous superficially and columnar in the deeper layers
Centrally five layers of cells, 10 at limbus
What is Bowman’s layer
Acellular layer consisting of interwoven collagen fibres
What is corneal stroma made up of? What proportion of corneal thickness is stroma?
Type I Collagen fibres arranged in a regular lattice
90%
Where is the stroma stongest?
The anterior corneal stroma has greater mechanical strength than the deeper layers of the stroma, because the lamellae anteriorly are thinner and more inter-woven.
What is Descemet’s made up of?
Collagen fibres arranged in hexagonal pattern
Basement membrane of the cornea
What cells form endothelium?
Cuboidal cells
What layer cells possess microvilli?
Surface epithelium and endothelium
What links adjacent cells in epi and endothelium
Desmosomes
Hemidesmosomes connect cells to their basement membranes
How does corneal epithelium regnerate?
Occurs at limbus with migration of cells to cover any defect
What are the epithelium and endothelium continuous with?
Epithelium continuous with the conjunctiva at the limbus
Endothelium continuous with the lining of the trabecular meshwork
What is the innervation of the cornea
Long ciliary nerves
From ophthalmic division of trigeminal V1
Form annular plexus of myelinated fibres at the corneal limbus with radial branches extending from this plexus into the corneal stroma to form a subepithelial plexus.
Divisions from this plexus pierce Bowman’s layer to form an intraepithelial plexus of unmyelinated nerves.
