Histology of Cornea and Corneal Dystrophies

Prefix: kerat-

Definition: The cornea is a transparent, avascular, watch-glass like structure which forms anterior one-sixth of the outer fibrous coat of the eyeball and covers iris, pupil and anterior chamber.

Histology:

cornea histology schematic

It consists of 5 distinct layers which can be remembered using the mnemonic “ABCDE“:

LayersThickness (µm)CompositionPathophysiology
Anterior epithelium50a. Top: 3-4 layers of squamous cells (uppermost are apical cells)b. Middle: 1-3 layers of wing cells (flattened polygonal shape)

c. Deep: 1 layer of basal cells

d. Basal lamina: scaffold for epithelim; collagen type IV; secreted by basal cells

Epithlial basement membrane dystrophy (AD)

Meesmann’s (AD)

Bowman’s membrane8-14Unorganized type I collagen fibers  in GAG matrix
Acellular
Reis-Buckler’s (AD)
Corneal stroma (Substantia propria)500 (~90%)~ 80% water by weightParallely organized lamellae of collagen I, IV and V in mucopolysaccharide matrix

Cells: Keratocytes, Langerhans’ cells, pigmented melanocytes, macrophages, histiocytes

Only MMP-2 is found in healthy cornea

Granular (AD)

Macular (AR)

Lattice (AD)

Descemet’s membrane10-12Anterior organized fetal banded layer (no change with age 3 µm)Posterior unorganized non-banded layer (thickens with age 2-10 µm)

PAS + true basement membrane

Endothelium5Single layer of interdigitating hexagonal cells (It is a misnomer as the cells are not endothelial cells)Schwalbe’s line: termination of corneal endothelium (junction between endothelium and trabecular meshwork)

Posterior embryotoxon: thickening and anterior displacement of Schwalbe’s line

Posterior polymorphous corneal dystrophy (AD)

Fuch’s dystrophy (AD)

Corneal Wound Healing in Short:

Epithelium: by migration and mitosis; rapid (starts 24-48 hours and completed by 6-8 days)

Stroma: non-complicated wound (avascular healing); complicated wound (vascular healing)

Descemet’s membrane and endothelium: slow regeneration

  1. Endothelium: mitosis and migration
  2. Descemet’s membrane: replacement by hyaline material derived from endothelium

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