Corneal Anatomy Flashcards
Where does the cornea meet the sclera?
The limbus
The cornea is transparent: true or false?
True
unlike the sclera the cornea is transparent and forms the outer most fibrous layer of the eye.
What is the refractive power of the cornea?
The cornea has the highest refraction power of the eye, at 40D, its refractive index is 1.376
What is the average diameter of the cornea?
Adults - 10-13 mm
Newborns - 9.5 -10mm
Is the cornea thicker at the centre or periphery?
Peripheries
At the centre it is roughly 535um thick, and becomes thicker (660um) towards the peripheries
The cornea is an ______ structure
Avascular
Where does the cornea receive most of its nutrients from?
The aqueous humour posteriorly and some from the tear film anteriorly
The cornea is highly sensitive. From what nerve does it receive its sensory supply?
CNV1 - via the long ciliary nerves
How many layers are there in the cornea?
5
List the layers of the cornea?
- Epithelial
- Bowman
- Stromal
- Descemet membrane
- Endothelium
Describe the epithelial layer of the cornea:
Stratified, non-keratinized squamous epithelium with a high regenerative potential to injury
What is the epithelial layer of the cornea highly regenerative?
This is due to the presence of limbal epithelial stem cells
Describe the bowman layer of the cornea:
This is an avascular layer with no regenerative ability. I contains the collagen fibres and terminates at the limbus
What layer of the cornea is the thickest?
The stromal layer
Describe the stromal layer of the cornea:
This layer also has no regenerative potential and is prone to scarring. It contains collagen type I fibres and keratinocytes. It I continuous with the sclera at the limbus
What layer of the cornea is an elastic layer containing type IV collagen fibres?
The Descemet layer
How does the endothelium of the cornea function?
By pumping any excess fluid from the stroma to keep the cornea dehydrated, maintaining its transparency.
This is a term used to describe a group of progressive hereditary disorders which cause corneal opacification and can lead to visual impairment.
Corneal dystrophies
Divided into anterior, stromal and endothelial
What are some examples of anterior corneal dystrophies:
Cogan (map dot) dystrophy (most common)
Reis-Buckler Dystrophy
What are some features of Cogan Dystrophy
Usually seen in the second decade of life
Bilateral recurrent corneal erosions
Sub epithelial geographic opacities with intraepithelial microcysts and sub epithelial ridges
What are some features of Reis-Buckler dystrophy?
AD condition which occurs as a result of the replacement of the Bowman’s layer with connective tissue
Recurrent corneal erosions in childhood - becomes less painful with age due to decreased corneal sensation
Sub epithelial opacities seen centrally
What are the three types of stromal dystrophies?
Lattice
Granular
Macular
(To help remember the features = Marilyn Monroe Always Gets Her Men in LA County)
What features are classic of macular stromal dystrophy?
MMA Macular dystrophy Mucopolysaccharide accumulate in stroma Alcian blue stain (features = grey poorly demarcated opacities of the stroma, bilateral vision loss in the first decade of life)
What are the features of granular dystrophy?
GHM Granular Hylaine deposits in the stroma Masson trichome - stains hyaline (features = dVA, recurrent corneal erosions, breadcrumb like opacities)
