Artificial tear composition and promotion of recovery of the damaged corneal epithelium.

In severe dry eye syndromes the corneal epithelium is compromised with development of punctate erosions and increased permeability. In the present study the ability of artificial tear solutions to promote recovery of the corneal epithelial barrier was determined by measurement of corneal uptake of 5,6 carboxyfluorescein (CF). Corneas of anesthetized rabbits were exposed to 0.01% benzalkonium for 5 min to increase epithelial permeability. The cornea was then exposed to an artificial tear solution for 1.5 h followed by measurement of CF uptake. During exposure to three commercial isotonic, nonpreserved solutions and a solution preserved with polyquaternium-1, CF uptake decreased significantly but did not return to control. No recovery of the epithelial barrier occurred during exposure of corneas to nonpreserved hypotonic solutions. During exposure to an experimental tear solution with an electrolyte composition similar to human tears, buffered with bicarbonate, CF uptake returned to control levels. Bicarbonate is an essential component of this solution because the same formula buffered with borate or without buffer was ineffective in promoting recovery of the damaged corneal epithelium.