- cornea.

cornea

* Definition :

It is a colorless (transparent) structure

covering the anterior 1/6 of the eye ball.


*Development of the cornea:

• Surface ectoderm forms the epithelium of the cornea.
• Mesoderm gives rise to the corneal stroma.
• Neural crest cells gives rise to the corneal Endothelium.

**Characters of the cornea :-

- colorless (transparent) structure and has a smooth surface.

- A vascular structure.

- Highly innervated by non-myelinated trigeminal nerve fibers.

-The most powerful refractive media of the eye

( 42+ diopters ).

- Diameter :-

• Horizontal = 12mm 
• vertical = 11mm Why…?

Due to scleral overlapping on upper

& lower sides of the cornea.

- It is not uniformly curved How…?

>>the central or optical zone having a smaller radius of

curvature than the peripheral parts,and the

posterior surface is more strongly curved than the anterior.

>> Ant radius of curvature = 7.7 mm 

>> Post radius of curvature = 6.6 mm

>>Thus the cornea is thinner (0.6 mm) at its

center than near its margin (1 mm).

see you,

Dr Ibrahim

- Development of eye lids.

Development of eye lids

Time :

Begins during 6th week.

process:

1- Eye lids develop from two folds of skins over the

cornea during 6th week.

2- Eye lids adhere to each other by the beginning of 10th week

& remain adhered till 26th to 28th weeks.

Congenital anomalies:

usually congenital anomalies appear together

to give a syndrome.

1-congenital ptosis:-

cause: failure of development of levator palpebrea

superioris muscle.

- It may be simple( alone).

- It may be associated eith other lid deformities or

congenital opthalmoplegia.

- it is usually bilateral & hereditary.

2- Epicanthus:

- is a semilunar skin fold at the side of the nose

covering the medial canthus & the caruncle leading

to false convergent squint.


3- Telecanthus:

increased distance () two medial canthi.

4-Blepharo-phimosis:

-Diminution of the horizontal width of the palpebral

fissure from 25-30 mm (normal) to 18-22mm without

pathologic changes in the eyelids.

- It is rare & usually asscociated in

Blepharo-phimosis syndrome.

5-Blepharo-phimosis syndrome:

presence of congenital ptosis,Epicanthus,

elecanthus & Blepharo-phimosis with each other.

6- Congenital trichiasis ( distichiasis)

- rare condition.

- In which abnormal extra raw of lashes replacing white line.

7- Congenital entropion:

- rare with micropthalmos.


8- Congenital ectropion:

- rare with Blepharo-phimosis syndrome.


9- coloboma of the eye lids:

- It is triangular , quadrilateral or

irregular shaped defect of the lid margin.


10- Epiblepharon:

-horizontal redundant medial fold of skin of the

eye lid inducing vertical orientation of the cilia.

-Epiblepharon may co exist with entropion.

-It usually imrpoves by age as the eyelid skin stretches.