Chapter 2 Terms

Question 1

Stroma:

Answer 1

480- 500 micron thickness- centrally
800 micron peripherally/90% of total corneal thickness.
-composed of collagen fibrils/ Keratocytes /ground substance.
-Collagen fibrils have a uniform diameter, forming flat bundles called ‘Lamellae’
- 200- 300 lamellae/organized/parallel to the surface/Transparency is maintained.
- Stromal cells are called ‘keratocytes’ – (corneal fibroblasts)-lie between the lamellae.
- Ground substance/fills the area between cells and lamellae/GAG (glycosaminoglycan – a glycoprotein molecule).
- 78% water by weight. Water molecules penetrates easily!
- Structural support- Rigid layer
- Heals , but Opacity is permanent?! – regenerates?

Question 2

Descemet’s membrane:

Answer 2

3 to 12 micron thickness/a basement membrane/highly resistant to trauma/produced constantly/gets thickened as the age advances.
Regenerates after damage – as long as endothelium is intact

Question 3

Corneal keratocytes (corneal fibroblasts)

Answer 3

are fibroblasts residing in the stroma.

Question 4

Fibroblast

Answer 4

is a type of cell that synthesizes the extracellular matrix and collagen, the structural framework (stroma) and plays a critical role in wound healing.
Apoptosis (death)of keratocytes- in case of injury
Excessive keratocyte apoptosis may be a part of the pathological process in the degenerative corneal disorders such as keratoconus?

Question 5

Epithelium

Answer 5

50 micron thickness/stratified epithelium/continuous with conjunctiva/3 layers- surface cells/wing/basal cells/
surface cells contains non-keratinized Squamous cells
(10% thickness of the Cornea)
Hydrophobic (Lipid molecule penetrates!)
Aerobic metabolism –O2 Via Tear film/accounts for
70% ATP Production
“Pin Prick” – 48 hours (not deep) -mitosis
Smooth surface protects the cornea
from infection
Regenerates – from limbal cells (turnover 6-7 days)

Question 6

Bowman’s membrane

Answer 6

10 micron ( micron=1/1000 of a mm) – single cellular
      Dense, fibrous sheet of interwoven collagen fibrils 
     A transition layer to the stroma/not a true membrane– contains fibrils/small diameter
      Toughest layer (flexible)! – Protects stroma/very resistance to penetration/infection
     Heals with scarring - doesn’t regenerate!

Question 7

Endothelium

Answer 7

4-6 micron thick/1 million cells at birth- loss of 50% with aging.
Monocellular layer/ doesn’t regenerate/cells don’t divide
Cells migrate and cover the defect!
Forms a weak Barrier between stroma and anterior chamber – allows nutrients from aqueous humor.
Keep cornea dehydrated and clear/Na+ K pump
PLEOMORPHISM –Variation in cell shape
POLYMEGATHISM- Variation in cell size (PMMA wear)

Question 8

Source of metabolites:

Answer 8

• Prelimbal blood vessels
• Aqueous humour
• Tear liquid + atmospheric Oxygen
• Deprivation of Oxygen leads to ‘Sattler’s veil’. (Swelling and Clouding of Superficial Cornea)

Question 9

Metabolic process

Answer 9

Carbohydrate metabolism
Glucose is the principal source of energy
Glycolysis – Breakdown of glucose molecules – Krebs cycle – 36 ATP (aerobic)
Aerobic and Anaerobic metabolism
Anterior cornea- Aerobic metabolism (glucose+ Oxygen based)
Posterior cornea – Aqueous humor

Question 10

Corneal Metabolism

Answer 10

Epithelium and endothelium – Glycolysis – High metabolic activity
Stroma shows very little metabolic activity
Epithelium – Aerobic metabolism – more energy is released – sodium-potassium pump used maximum energy!
In the absence of Oxygen – cornea swells and loses its transparency