Cell Growth

Stem cells

• Arise during the embryonic period and produce daughter cells 
• Subtypes:
• Multipotent: give rise to many different cell types
• Unipotent: limbal stem cells can only give rise to corneal epithelial cells
• Stem cells are found in specific sites within tissues

Growth factors

• Epidermal growth factor: autocrine control of corneal epithelial turnover
• Stimulates corneal epithelial migration and proliferation
• Transforming growth factor beta: three forms and many roles
• Inhibits epithelial proliferation
• Differentiation of conjunctival to corneal epithelium
• Proliferation of stromal fibroblasts
• Increased collagen synthesis
• Platelet derived growth factor: limbal stem cell proliferation
• Fibroblast growth factor: epithelial and fibroblast proliferation

Extracellular matrix

• Collagen
• Laminin
• Located in basal lamina
• Re-synthesised within 48 hours of corneal trauma under migrating cells
• Fibronectin
• On the stromal side of Descemet’s membrane
• Promotes adhesion between cells via integrins
• Stimulated by EGF and TGF

• Deposited on bare stromal surface within moments of epithelial injury to act as a temporary scaffold

• Integrins
• Transmembrane glycoproteins present in almost all cells
• Mediate cell-ECM and cell-cell attachments
• Can also convey biochemical signals
• Disruption of normal integrin-ECM interactions prevents normal eye development