Corneal Anatomy

Question 1

Where does the cornea meet the sclera?

Answer 1

The limbus

Question 2

The cornea is transparent: true or false?

Answer 2

True

unlike the sclera the cornea is transparent and forms the outer most fibrous layer of the eye.

Question 3

What is the refractive power of the cornea?

Answer 3

The cornea has the highest refraction power of the eye, at 40D, its refractive index is 1.376

Question 4

What is the average diameter of the cornea?

Answer 4

Adults - 10-13 mm

Newborns - 9.5 -10mm

Question 5

Is the cornea thicker at the centre or periphery?

Answer 5

Peripheries

At the centre it is roughly 535um thick, and becomes thicker (660um) towards the peripheries

Question 6

The cornea is an ______ structure

Answer 6

Avascular

Question 7

Where does the cornea receive most of its nutrients from?

Answer 7

The aqueous humour posteriorly and some from the tear film anteriorly

Question 8

The cornea is highly sensitive. From what nerve does it receive its sensory supply?

Answer 8

CNV1 - via the long ciliary nerves

Question 9

How many layers are there in the cornea?

Answer 9

5

Question 10

List the layers of the cornea?

Answer 10

• Epithelial
• Bowman
• Stromal
• Descemet membrane
• Endothelium

Question 11

Describe the epithelial layer of the cornea:

Answer 11

Stratified, non-keratinized squamous epithelium with a high regenerative potential to injury

Question 12

What is the epithelial layer of the cornea highly regenerative?

Answer 12

This is due to the presence of limbal epithelial stem cells

Question 13

Describe the bowman layer of the cornea:

Answer 13

This is an avascular layer with no regenerative ability. I contains the collagen fibres and terminates at the limbus

Question 14

What layer of the cornea is the thickest?

Answer 14

The stromal layer

Question 15

Describe the stromal layer of the cornea:

Answer 15

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

Question 16

What layer of the cornea is an elastic layer containing type IV collagen fibres?

Answer 16

The Descemet layer

Question 17

How does the endothelium of the cornea function?

Answer 17

By pumping any excess fluid from the stroma to keep the cornea dehydrated, maintaining its transparency.

Question 18

This is a term used to describe a group of progressive hereditary disorders which cause corneal opacification and can lead to visual impairment.

Answer 18

Corneal dystrophies

Divided into anterior, stromal and endothelial

Question 19

What are some examples of anterior corneal dystrophies:

Answer 19

Cogan (map dot) dystrophy (most common)

Reis-Buckler Dystrophy

Question 20

What are some features of Cogan Dystrophy

Answer 20

Usually seen in the second decade of life
Bilateral recurrent corneal erosions
Sub epithelial geographic opacities with intraepithelial microcysts and sub epithelial ridges

Question 21

What are some features of Reis-Buckler dystrophy?

Answer 21

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

Question 22

What are the three types of stromal dystrophies?

Answer 22

Lattice
Granular
Macular
(To help remember the features = Marilyn Monroe Always Gets Her Men in LA County)

Question 23

What features are classic of macular stromal dystrophy?

Answer 23

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)

Question 24

What are the features of granular dystrophy?

Answer 24

GHM
Granular
Hylaine deposits in the stroma
Masson trichome - stains hyaline
(features = dVA, recurrent corneal erosions, breadcrumb like opacities)

Question 25

What are the features of lattice dystrophy?

Answer 25

LA County
Lattice dystrophy
Amyloid deposits in the stroma
Congo red staining 
(features = reduced corneal sensation, recurrent corneal erosions, anterior glassy stromal dots affecting centre which form fine filamentous lines)

Question 26

Endothelial dystrophy - Fuchs’, is the most common corneal dystrophy. Give some features of it:

Answer 26

AD
Common in elderly females
Due to failure of the Na+/K+ pump which causes accumulatio of fluid in the cornea = cell loss
Blurry vision worse in mornings
Pachymetry may show increase CCT
Specular microscopy will show corneal guttata and low endothelial cell counts