Corneal Epithelium and Basement Membrane

Corneal Epithelium

• Comprises about 10% of the corneal thickness
• Consists of 5 or 6 cell layers
• Basal cells have a high proliferative capacity for renewal and repair of the corneal surface
• Stem cells in the corneoscleral limbus give rise to basal cells
• Flattened surface cells have microvilli protruding into a protective tear film of lipid, glycoprotein, and water
• Has one of the richest sensory nerve supplies of any tissue

Basement Membrane (Bowman's Membrane)

• Very thick (8-10 μm)
• Contributes to the stability and strength of the cornea
• Helps protect against infection of the underlying stroma

Corneal Stroma (Substantia Propria)

• Makes up 90% of the cornea's thickness
• Consists of approximately 60 layers of parallel collagen bundles
• Collagen bundles aligned at approximately right angles to each other
• Collagen fibrils extend almost the full diameter of the cornea
• Uniform orthogonal array of collagen fibrils contributes to the transparency of the avascular tissue

Keratocytes and Ground Substance

• Keratocytes are flattened fibroblast-like cells
• Cytoplasmic extensions of keratocytes are found between the collagen lamellae
• Ground substance around keratocytes contains proteoglycans such as lumican, with keratan sulfate and chondroitin sulfate
• Proteoglycans help maintain the precise organization and spacing of the collagen fibrils