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Isolated rabbit corneas were bathed on their endothelial surfaces with normal Krebs bicarbonate Ringer solution, while the epithelial surfaces were bathed in a basic tear solution containing sodium and potassium. When bathed in basic tear solution alone, corneal swelling occurred at an average of 12 μm/h over a 3-hour period. Corneal swelling occurred at a rate of about 21 μm/h when the epithelial solution was switched from normal basic tear solution to an iso-osmotic K⁺-free basic tear solution. Corneal swelling then slowed, and in the final hour of a 3-hour exposure to K⁺-free tear solution, the corneas deswelled at about 10 μm/h. The data indicate that potassium is a necessary solute for the maintenance of normal corneal thickness. The results suggest that a lacrimal dysfunction that would cause a decrease in the potassium content of tears may influence corneal thickness and also suggest that the inclusion of potassium in artificial tears is important.

An average chlorhexidine concentration of 4·5 μg mg−1 lens (wet weight) was measured in HEMA‐based contact lenses after 16 days of the following treatment. The lenses were maintained 16 h daily in 1·5 ml of a solution containing Chlorhexidine digluconate 0·005%, and then worn by adult albino rabbits 8 h daily. Similarly maintained, but unworn lenses contained approximately 23 μg Chlorhexidine mg−1 wet lens weight after 16 days. A plot of the results indicates that continued exposure to Chlorhexidine following initial immersion increased its concentration in unworn lenses while that in the worn lenses reached a peak at 8 days, then decreased slightly in the subsequent days of wearing. Continuous exposure of lenses to the disinfecting solution (1 lens/167 ml) in which the Chlorhexidine concentration was maintained at 0005% for 16 days gave a maximal concentration of 44 μg mg−1 wet lens weight. The comparatively small concentration in a worn lens results from: (1) daily loss from the lens during wear, a large percentage of which is apparently absorbed to tear proteins which subsequently flow from the eyes via the canaliculi; (2) limited uptake because of the small immersion volume employed in routine storage; and (3) the possible competition between Chlorhexidine and tear components for lens binding sites or establishment of an equilibrium condition between uptake and release.

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