The hydration of cornea is kept in balance by opposing forces:
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.
the stromal swelling pressure
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:
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.
there is pump failure as in Fuchs' endothelial dystrophy
intraocular pressure of above 50mmHg