Introduction: Factors influencing corneal hydration

The swelling of the corneal buttons in aqueous solution can be prevented by adding high molecular weight solutes to the bathing medium. In appropriate concentrations of these colloidal substances the button can be dehydrated, a matter of some significance in clinical situations. Swelling of the cornea in the intact eye in vitro can be similarly prevented. The suggestion is made that swelling is due to Donnan osmotic pressure of the cornea. Current evidence favors the view that the swelling potential is present in vivo and that normal corneal hydration is maintained by secretion of fiuid. The rate of secretion seems adequate to maintain normal corneal hydration in close proximity to a corneal puncture.