Cornea

Aka: Cornea, Corneal Epithelium, Bowman's Membrane, Corneal Stroma, Corneal Endothelium, Descemet's Membrane

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II. Definitions

  1. Cornea
    1. Transparent front refractive window of eye
    2. Cornea's steep curvature provides most of Refraction needed to direct light onto Retina
      1. Lens performs fine, variable focus adjustments

III. Anatomy

  1. eyeGlobeXsGrayBB869.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  2. eyeCorneaLensGrayBB883.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)

IV. Physiology

  1. Dimensions
    1. Vertical: 11.6 mm
    2. Horizontal: 11.5 mm
    3. Thickness
      1. Peripheral: 1 mm
      2. Central: 0.55 mm
  2. Five distinct layers
    1. Epithelium (Exterior layer of Cornea, a few cells thick)
      1. Prevents infection
      2. Smooth refractive surface
      3. Produces the tear film
      4. Continually regenerates
    2. Bowman's Membrane
    3. Stroma (90% of Corneal thickness)
      1. Composed of Collagen fibrils intertwined
      2. Supportive structure of Cornea
    4. Endothelium
      1. Dehydrates Cornea via Na-K ATP Pump
      2. Relative Dehydration maintains Corneal clarity
    5. Descemet's Membrane (Interior Layer of Cornea)
      1. Endothelium basement membrane
  3. Function
    1. Barrier protection
    2. UV light filtration
    3. Refraction
      1. Cornea provides 65-75% of eye's focusing power
      2. Lens performs remainder of focus, the fine, variable focus adjustments
        1. Unlike the lens, the Cornea's Refraction power is fixed
      3. Contact Lenses modify the Corneal surface to optimize non-variable focus
  4. Blood supply
    1. No direct blood supply to maintain transparency
    2. All nutrition supplied indirectly
      1. Tears
      2. Ambient oxygen
      3. Aqueous Humor of anterior chamber

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