Cornea

Question 1

What is Cornea

Answer 1

A transparent avascular connective tissue with smooth surface. main structural barrier to infections. Eyes principal refracting component along with overlying tear film - makes up 2/3 of eyes refracting power -43D . RI-1.33
Steeper in centre flatter at edges. Continuous with sclera and conjunctiva.

Question 2

Epithelium-1

Answer 2

Epithelial cells replace every 7 days.
Comprised of flattened superficial squamous cells , intermediate less flattened wing cells and innermost layer of cuboidal basal cells. Superficial squamous cells have small projections called microplicae. Mucin from goblet cells cover microplicae to form the innermost layer of tera film. Tear film is important as contributes to refractive power of cornea and washes away viruses, debris and pathogens from eye and smooths out epithelial micro irregularities. all are related as basal cells move anteriorly and differentiate into squamous cells takes about ten days
Basal and wing cells are connected by anchoring junctions and squamous cells are linked by same- zonula occludens. Anchoring junctions are part if first line of defence against pathogens and allergens.
The plasma membrane of the surface epithelial cells secrets a gylcocalyx component which bind mucin to cornea making it hydrophilic.

Question 3

Bowmans layer/ membrane -2

Answer 3

smooth acellular transition zone. Randomly arranged collagen fibrils. helps cornea maintain its shape/ rigidity

Question 4

Stroma-3

Answer 4

90% of corneal thickness and main contributor to corneal transparency. Composed of type 1 and type 5 collagen arranged in uniform bundles called lamellae -precice organisation , has PGs running between it which regulate hydration . also contains keratocyes which synthesise collagen and GAGs , things that make up ECM , which crucial to maintain ECM homeostasis so haps transparency and healing . Keratcocytes at ant stroma contain corneal crystallins which reduce light backscatter from keratocytes so helps transparency. Excessive cell death of keratoytes leads to keratoconus which is steep thinning of cornea. periphery thicker than centre.

Question 5

Descemets Membrane- 4

Answer 5

Latticework of collagen produced from endothelium provides structural support for endothelium . produced continuously so thickens throughout lfe. ends at limbus called schwalbes line.

Question 6

Endothelium - 5

Answer 6

innermost layer of hexagonal cells that don’t divide or replace so numbers decrease with age.
Slightly leaky barrier to allow entry of nutrients from AH.
Metabolic pump to allow movement of ions across membranes.

Question 7

Corneal nerve supply

Answer 7

Most innervated structure in human body - most sensitive tissue in body- feels pain, temp, touch. Innervated by 1 st cranial nerve and by way 70-80 long ciliary nerves.
Most nerves terminate at epithelium.

Question 8

What are the different things that apply to the corneal transparency

Answer 8

cornea transmits nearly 100% of light that enters it.
1- arrangement of stroma lamellae
2- uniform arrangement of epithelium
3- avascularity
4- relative state of hydration
4- keratocytes via ECM regulation

Question 9

Dehydration

Answer 9

NAK ATPase pump at endothelium. Normal cornea maintains a state4 of relative dehydration (78%) H20.
Nutrients to maintain transparency and for dehydration come from leaky barrier of aqueous jumolour.
To maintain dehydration pump takes Na and H20 out of cell. Bicarbonate ions formed by the action of carbonic anhydrase are translocated across membrane allowing H20 to passively follow. If cornea swells transparency is lost as there is light scatter.
Oedema- swelling caused by water usually

Question 10

Vascularity and nutrition

Answer 10

Avascular so good for transplants . no lymphatics
Nutrition glucose, amino acids vitamins are from AH from leaky barrier .
02 comes mainly from air via tear film.