Cornea Flashcards
What is the power of anterior corneal surface?
Posterior? Total
Anterior 48.8D
Posteiror -5.8D
Total 43 D
What meridian has the shorter radius of curvature?
Vertical meridianWhat are teh layers of the cornea?
Where is the cornea steepest?
Centrally
refractive index?
1.376
What are the layers of the cornea?
EPithelium
Bowman’s membrane
Stroma
Descemet’s
Endothelium
How thick is Descemet’s
10um
Are junctions tight or loose between endothelium?
Tight to control corneal hydration
Where does corneal epithelium get glucose? Oxygen
Oxygen from tear film
Glucose from the stroma
Where is most carbohydrate catabolism done in cornea?
Endothelium - rich in mitochondria
What happens to lactic acid produced in the cornea?
Diffuses slowly from the stroma and endothelium into the aqueous
What % of cornea is water?
75-80%
How does IOP affect corneal hydration?
Above 55mmHg can cause corneal oedema
What is the predominant type of collagen in thecorneal stroma?
Type I
What prvides collages stregth?
Intermolcular cross-links
Hydroxylysineorleucine is the major reducible cross link
How does diamater of collagen fibril and spacing change throughout the cornea
Constant
What are proteoglycans?
Glycosylated proteins - repeated disaccharides
Bind to collagen fibrils and regulate spacing
What is the most common conreal proteoglycan?
Keratan sulphate - 60%
Dermatan - 40%
What happens to collagen in corneal scarring?
Width decreases and number of glycoside residues increase - opacity is reduced
Ratio of keratan:dermatan decreases in scars - distortion of regular arrangement of collagen fibrils
What are MMPs? What metal?
Matrix metalloproteinases - break down components of extracellular matrix - remodelling after injury
Zn 2+
Which MMP is found in helathy cornea? What do they do?
MMP2 - active against Type IV, V, VII collagen
MMP1, 3, 9 after corneal injury
What does lactic acid accumulation in the cornea manifest as?
Corneal oedema
SLActatebuilds up due to anaerobic respiration e.g. over wearing of ill fitting contact lenses preventing O2 from tear film
Only small amount of lactate removed through tears, most must diffuse through stroma and endothelium to aq = build up
Osmotic shift pulling water into corneal strome = oedema
Lactate pumped into aq - by H+ lactate pump - increaseed acidification of cornea - potassium loss, cell shrinkage, apoptosis
Corneal endothelial cell density in adult
3000cell/mm2
How deos the cornea change overnight?
4-8% thicker due to relative hypoxia resulting in swelling
What joins the basal columnar layer of the corneal epithelium to the basal lamina?
Hemidesmosomes
