Cornea : easy and brief description

Cornea:

Cornea is a miracle structure of our body. It is a living avascular, wet, transparent structure.

Development: 

The tissue of eyeball are derived from neuroectoderm, surface ectoderm & mesoderm. 

1. The corneal epithelium ( non-keratinized stratified squamous epithelium ) is developed from surface ectoderm 
2. Stroma of cornea (rest of the layers of cornea)  is developed from mesoderm 

Features of cornea:

1. avascular 
2. rich in nerve supply by long ciliary nerve - branches of ophthalmic division of trigeminal nerve 
3. transparent 

How it get nutrition: 

1. aqueous humor
2. tear

Histological features of cornea : 

The cornea consists of five layers (outward to inward ) 

1. Corneal epithelium: non-keratinized stratified squamous epithelium 
2. Bowman's membrane (anterior basement membrane) 
3. Corneal stroma: substantia propria 
4. Descemet's membrane 
5. Corneal endothelium 

Features of corneal epithelium :

1. Non-keratinized stratified squamous with five layers of cells, basal cells are low columnar and surface cells are squamous with microvilli with helps to spread tear on corneal surface 
2. it is continuous with conjunctiva 
3. it has remarkable capacity to regenerate, it correct superficial injury with 24 hrs and its turnover time: 7 days 
4. stem cells of cornea are situated at sclero-corneal junctions, these cells prevent conjunctivalization of corneal epithelium 
5. it is innervated by numerous free nerve ending, pain receptors of cornea is 300-600 times greater than the skin and 20-40 times greater than the dental pulp, so pain sensation is the only sensation in cornea 
6. it contain no melanin pigmentation, but corneal cancer is very rarely seen. how corneal DNA protected from UV light ?
7. corneal epithelial cells nuclei contain ferritin an iron storage protein which protect DNA of corneal epithelium from UV light 

What do you mean by conjunctivalization of corneal epithelium: 

1. the corneal epithelium become vascular 
2. appearance of goblet cells 
3. irregular and unstable cells 

Bowman's membrane : 

1. Homogeneous 
2. collagen fibrils (no collagen fibre)  of it randomly oriented 
3. it has no capacity to regenerate 
4. it support cornea 
5. damage of this structure causes opacity 

Corneal stroma: substantia propria 

1. it is the thickest layer of cornea (about 90%)
2. it is formed by 60 lamellae 
3. each lamella contain parallelly arranged  collagen fibrils, this contribute transparency of cornea, this regular arrangement is lost in any injury of cornea causes opacity  
4. the collagen fibrils in each lamella are arranged at right angles to adjacent lamella 
5. fibroblasts are situated in between lamellae 
6. 
   

Descemet's membrane : 

1. it is consider as basal lamina of corneal endothelium 
2. it has the capacity to regenerate 
3. it maintain curvature of cornea 

Corneal endothelium

1. it is formed by simple squamous epithelium 
2. it maintain water contain of cornea 
3. it has limited capacity to regenerate 
4. damage of it causes swelling of cornea, collagen fibrils arrangement  in lost, cornea become opaque 
5. severely damage corneal endothelium is repaired by corneal transplantation