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    Default THE CORNEA (Anatomy - Physiology - Transparency - Nerve Supply)

    THE CORNEA




    Anatomy of the Cornea

    • 11.5 mm horizontal diameter
    • 10.5 mm vertical diameter
    • 1 mm thick periphery
    • 0.5 mm thick centrally
    • Anterior surface radius 7.7 mm
    • Posterior surface radius 6.8 mm

    ✍️ Epithelium

    • Stratified squamous, nonkeratinized, nonsecretory epithelium (keyword)

    • 5–6 layers

    • Superficial cells have microvilli (needs
    tears to keep cornea smooth)

    • Basement membrane (strongly attached
    to Bowman’s layer )

    • Regenerate from the limbal stem cells at the limbus

    CORNEA (Anatomy Physiology Transparency Nerve attachment.php?attachmentid=3433&d=1510565793

    ✍️ Bowman’s layer

    • 8-12 μm

    • Acellular

    • type IV collagen

    •Don’t regenerate , replaced by fibrous tissue if damaged (scars)

    • Ends abruptly at limbus

    ✍️ Stroma (substantial propia)

    • 90% of cornea thickness, 400 μm centrally

    • 80% water

    • Glycosaminoglycans in extracellular matrix

    - Keratan sulphate (50%)
    - Chondroitin phosphate (25%)
    - Chondroitin sulphate (25%)

    • posterior condensation of the stroma is newly called ( Dua layer)

    ✍️ Descemet’s membrane

    • Basement membrane of the endothelium
    (keyword)

    • 10 μm thick

    • Secreted and regenerated by endothelial cells

    • Type IV collagen

    • Hassall-Henle bodies( peripheral)

    • Terminates abruptly at limbus (Schwalbe’s
    line)

    ✍️ Endothelium

    • Single layer, polygonal, cuboidal cells

    • Tight junctions (control of corneal hydration)

    • Microvilli

    • Don’t regenerate

    • Repair occurs by cellular hypertrophy ( polymegacism)and sliding(polymorphism)

    • Line passages of trabecular meshwork

    Physiology of Cornea

    • Light transmission (400–700 nm light)

    • Light refraction:

    • 43 D (70% of eye’s refractive power)

    • Refractive index of cornea 1.376

    • Protective function to the globe

    • Cornea obtains glucose mainly from aqueous but tears and limbal capillaries appear to provide
    minimal contribution

    • Glucose can be stored in epithelium as glycogen

    • ATP obtained by glycolysis and Kreb's cycle

    • oxygen from aqueous or from either capillaries at the limbus or precorneal film

    Cornea Transparency due to

    • Relative dehydration of cornea by endothelium and epithelium

    • Endothelial pump removes fluids from stroma

    • Evaporation of water from tear increases
    osmolarity of tear, which draws water from cornea

    • Normal intraocular pressure (if too high, relative hydration occurs)

    • Relative acellularity, lack of blood vessels and pigments

    • Regular matrix structure of corneal fibrils

    • Destructive interference of light occurs

    • Consistent refractive index of all layers

    Nerve Supply

    • 5th CN ( ophthalmic division)

    • Long posterior ciliary nerves gives 3 plexuses

    - Annular plexus at limbus

    - Subepithelial plexus just below Bowman’s membrane

    - Intraepithelial plexus

    • Nerves loss it’s myelin just after entering the cornea











    Attached Images  
    Last edited by Reda Gomah El Garia; 11-13-2017 at 09:37 AM.

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