4. What factors affect corneal hydration? Discuss the role of the 
The hydration of cornea is kept in balance by opposing forces: 
  • the stromal swelling pressure
  • endothelial pump
The proteoglycans associated with collage fibrils in the stroma have water-attracting property. This gives rise to the swelling pressure. The swelling pressure which decreases with increasing stromal hydration and thickness. The normal value of swelling pressure is 55mmHg. 

To prevent corneal oedema from the excess fluid in the cornea. The water is removed by the endothelium pump.

The swelling pressure and the endothelium pump balance each other and prevent corneal oedema. This balance broke down if:

  • there is pump failure as in Fuchs' endothelial dystrophy
  • intraocular pressure of above 50mmHg 
The cornea epithelium forms an impermeable membrane. There are extensive close contacts and junctional complexes between the basal cells. Epithelial defect will results in mild and transient corneal oedema. Provided the endothelium pump is intact the oedema is removed quickly.
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