Corneal Repair Flashcards
What does corneal initiate
A cascade of mechanisms to repair damaged tissue, a process directed by various biomolecules
Integral membrane glycoproteins
Corneal integrins
Roles of corneal integrins
- facilitate interactions between cells and ECM
- matrix assembly
- impact cell adhesion and formation of intercellular junctions
- sense change in the extra cellular environment and communicate to the cell nucleus by an alteration in the cytoskeleton
Signaling molecules that are expressed in the normal and inflammatory cornea after infections, burns, etc
Cytokines
Roles of cytokines
- facilitate cellular communication between cells and surrounding tissues
- control the growth of the corneal cells
Roles of growth factors
- promote proliferation of corneal cells
- induce migration of corneal cells
- maintenance of corneal transparency
Which epithelial layer can cells divide
Basal layer
How many layers thick is the epithelium,
5-7 cells thick
What are the different cell layers in the epithelium and how thick is each layer
- surface layer: 2 cells thick
- wing layer: 2-3 cells thick
- basal layer: 1 cell thick
Epithelial replacement
- stems cells in peripheral cornea divide (mitosis)
- new cells move towards the center of the cornea to become basal cells
- basal cells move up to become wing cells
- wing cells move up to become surface cells
- surface cells shed into tear film
- 7 day turnover
Epithelial injury
- Mitosis stops, biomolecules get signaled
- growth factors and cytokines are released from damaged cells
- hemidesmosomes dissemble along wound edge
- changes in cytoskeleton (cell changes shape, cells at wound edges develop membrane extensions, cells migrate to cover wound)
- defect covered by a single layer of cells (cell-to-cell junctions formed between neighboring cells)
- mitosis resumed (proliferation continues until normal cell density is reached, apoptosis prevents epithelial hyperplasia)
- heidesmosomes replace biochemical bonds holding basal cells
During corneal epithelial injury, cell migration requires control of
- hemidesmosomes
- cytoskeleton structure
- cell-to-matrix adhesion
This preserves the structural integrity of epithelial sheet
Adhesion molecules in epithelium wound healing
- allows for epithelial sheet to adhere to basement membrane
- pulls cells forward as sheet covers wound area
- growth factors stimulate production of matrix components to enhance adhesion
- proliferation suppressed until migration occurs
Healing time frame of small lesion to epithelium
24–48 hours
Healing time frame for basement membrane damage of epithelium
Several months for normal hemidesmosomes adhesions
Is there a scar in epithelial wound healing
No
Corneal epithelium sloughs off either continually or periodically
Recurrent cornel erosion
Cause of recurrent corneal erosion
- poor adhesion between epithelium and basement membrane
- poor adhesion between basement membrane and underlying tissue
When does recurrent corneal erosion occur
After incomplete healing of an abrasion OR by epithelial basement membrane dystrophy
Treatment for recurrent corneal erosion
- artificial tears
- Abx
- bandage CLs
- anterior strongly micropuncture
- superficial keratectomey
- phototherapeutic keratectomy
Bowman’s layer
A cellular layer
- composed of collagen
- highly resistant to penetration or damage
Does bowmans layer regenerate?
No
Only one cell layer thick and does not regenerate
What is bowmans replaced by if it gets damaged
Storm all scar tissue or by the epithelium
90% of total corneal thickness
Stroma
What is the stroma composed of
- collagen fibrils (form lamellae)
- keratocytes (corneal fibroblasts)
- extracellular ground substance (fills between fibrils, lamellae, and cells)
Stroma wound healing: upon injury
Keratocytes increase in number; some stimulated to become myofibroblasts, cause wound bed to contract, wound coverage by epithelium
Regenerated stroma collagen
Is larger than the original fibrils and alignment and organization are not as precise, increasing probability of scarring
Stroma wound healing: after healing complete
Myofibroblasts undergo apoptosis or revert back to keratocytes
Healing time frame for stromal wouldn’t healing
Months
New collagen fibrils in stromal wound healing
Have diminished strength, months to reach typical strength
Basement membrane of endothelium
Descemet’s membrnae
Composed of collagen fibrils and produced constantly, thickens throughout life
Descemet’s membrane
What is the descemet’s membrane is regenerated by what
Stromal keratocytes and the endothelium
Layers of cells in endothelium
Single layer of flattened cells
Endothelium cell shape
Polyhedral
- 70-80% hex (5)
- 20-30% hept (7)
Cell orientation in the endothelium
- basal part rests on descemet’s membrane
- apical surface lines the anterior chamber
Mitosis and endothelial wound healing
Little mitosis occurs
Endothelial wound healing
- neighboring cells enlarge and flatten to cover area of cell loss, decrease in endothelial like cell density
- cells remodel into polyhedral shape
- pump and barrier functions are re established (increase in ion pumps to compensate for loss of pumps from cell loss)
