Eye

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Anatomy & histology-cornea



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Last staff update: 17 April 2024

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PubMed Search: Cornea anatomy and histology

Nat Pernick, M.D.
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Cite this page: Pernick N. Anatomy & histology-cornea. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/eyecorneaanatomy.html. Accessed May 19th, 2024.
Definition / general
  • Wider than tall (11.7 mm horizontally vs. 10.6 mm vertically)
  • Thickness varies from 0.5 mm (central) to 0.67 mm (peripheral)
  • Cornea and overlying tear film are major refractive surface of eye, not the lens
  • 6 distinct layers (outside to inside):
      1. Outer epithelium: stratified squamous, nonkeratinized, 5 layers thick centrally, thicker peripherally, polygonal at basal layer but flatten as they approach surface; basal cells may have mitotic figures; Langerhans cells are CD1a+; note: layers often rubbed off while grossing specimen
      2. Epithelial basal lamina (basement membrane): highlighted with PAS stain
      3. Bowman layer: most anterior stroma, acellular, 8 - 14 microns thick, not a true basement membrane, composed of randomly oriented delicate collagen fibers, does not regenerate
      4. Stroma: also called substantia propria, no blood vessels or lymphatics, 90% of cornea's thickness, contains regularly spaced collagen fibrils; normally separated by glycoprotein and mucoprotein which makes cornea transparent; normally see stromal lamellae separated by clefts, a processing artifact, absence of clefts is caused by stroma edema (causes corneal clouding), due to damage of endothelium
      5. Descemet [pronounced DEZMET] membrane: a true basal lamina produced by underlying corneal endothelial cells; 3 - 4 microns at birth, 10 - 12 microns in adults; does not regenerate; site of copper deposition in Kayser-Fleisher ring of Wilson disease
      6. "Endothelium": single layer of very flat cells, does not regenerate, functions as pump to keeps cornea dehydrated and transparent
        • Neural crest origin (S100+); does not line blood vessels or lymphatic spaces; directly contacts aqueous humor of anterior chamber, often rubbed off while grossing specimen
Hasall-Henle bodies (warts)
  • Focal excrescences that form on peripheral Descemet membrane with normal aging
  • Not seen in surgically excised corneal buttons because are too peripheral in location
Hyperopia
  • Eye too short for its refractive power
Laser assisted in situ keratomileusis (LASIK)
  • Sculpt cornea and change its refractive properties to eliminate need for glasses
Limbus
  • Junction of peripheral cornea and anterior sclera, 1.5 to 2.0 mm wide
  • Not a distinct anatomic site but a significant clinical landmark
  • Composed of conjunctiva (epithelium and stroma), cornea and scleral stroma, episclera, Tenon capsule (fibrous tissue that covers the globe)
  • Descemet membrane terminates at limbus and gives rise to Schwalbe ring
  • 15% have prominent area of thickening at this site
  • Contains trabecular meshwork and Schlemm canal
  • Site of incisions for surgery on anterior eye
  • Restricts deeper extension of superficial tumors
Myopia
  • Eye too long for its refractive power
Schlemm canal and trabecular meshwork
  • Schlemm canal
    • Anterior and superficial to trabecular meshwork
    • Endothelial lined venous canal that completely encircles limbus
    • Separated from trabecular meshwork by thin connective tissue and separate endothelial linings
  • Trabecular meshwork
    • With Schlemm canal, are apparatus for removal of aqueous from eye
    • Collection of finely branching and delicately pigmented connective tissue bands
    • Lining cells are continuous with corneal endothelium
    • Posteriorly, trabecular meshwork extends to scleral connective tissue called scleral spur
Vasculature
  • No blood vessels or lymphatics within cornea
  • Arterial plexus is present at junction of cornea and sclera
  • Is also nourished by aqueous humor of anterior chamber
Microscopic (histologic) images

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Full thickness

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Epithelium and Bowman layer

Drawings

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Cornea

Positive stains
Negative stains
Electron microscopy description
  • Schlemm canal endothelial cells contain giant cytoplasmic vacuoles
Additional references
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