LENS AND EYE TOXICITY RESEARCH, 6 (1&2), 37-41 (1989) PRESERVATIVE EFFECTS ON THE HEALING RATE OF RABBIT CORNEAL EPITHELIUM. Keith Green (1, 2), Robert E. Johnson (1), Jack M. Chapman (1), Elizabeth Nelson, and Lisa Cheeks Department of Ophthalmology and Department of Physiology and Endocrinology, Medical College of Georgia Augusta, GA 30912 - 3400 yABSTRACTz Benzalkonium chloride (BAK), sodium lauryl sulfate (SLS), chlorhexidene digluconate were tested for their effects on the rate of corneal epithelial regrowth after mechanical lesions, and BAK and SLS after heptanol-generated lesions in rabbit corneas. Only 1.3 % SLS reduced the rate of epithelial healing after three times a day drop application as determined using planar measures of epithelial regrowth. SLS, a common ingredient in soups and shampoos, should be used carefully where a lesions or would is present in the corneal epithelium. yINTRODUCTIONz The healing rate of rabbit corneal epithelium is well documented at 0.6 to 0.8 H/hr whether created by a mechanical or n-heptanol lesions (1-3). Healing is a biphasic process, with a short reconstructive phase followed by a linear regrowth phase (3). Since benzalkonium chloride (BAK) is known to alter the morphology of normal corneal epithelium (4), and also resides mainly in the epithelium after topical application (5) its effects on epithelial healing were sought. In addition, sodium lauryl sulfate (SLS) is also retained in the corneal epithelium (5) although, unlike BAK, it then penetrates all tissues of the eye and also reaches systemic tissues. The effect of SLS on corneal epithelial regrowth, as well as that of thimerosal, chlorhexidine digluconate and polyaminopropyl biguanide, was also examined. yMATERIALS AND METHODSz Corneal epithelial lesions were created in 2 to 3 kg rabbits sedated with ketamine / xylazine. Mechanical lesions were made by scraping cells from a trephined 6 mm diameter area, and chemical lesions were made using n-heptanol soaked filter paper (1). At intervals after creation of the lesion it was photographed after being delineated with fluorescein. Fifty ƒÊ1 drops of either BAK, at 0.004 or 0.02%; SLS at 1.3%, thimerosal, 0.001%; chlorhexidine digluconate, 0.005%, or polyaminopropyl biguamide, 0.00005% (ReNu contact lens disinfecting solution) were applied three times daily. The contralateral eye served as a control and received 0.9% saline. The area of the lesion was determined from the projected photograph, after being measured from a trace of the outline of the lesion, using a computer graphics pad. The area of each successive lesion was converted into a percentage of the original lesion area for each eye. Corneas were used for either determination of 14C-sucrose permeability or for scanning or transmission electron microscopy. yRESULTSz Both mechanical and n-heptanol-created lesions of the rabbit corneal epithelium healed at 0.6 mm^2 / hr. BAK, at both concentrations, has no effect on corneal wound healing after mechanical or chemical lesions; neither thimerosal, chlorhexidine digluconate nor polyaminopropyl biguanide had any effect on wound healing after mechanical lesions (n-heptanol lesions were not examined with these latter agents). SLS caused marked effects on epithelial regrowth in both mechanical and chemically created lesions, with more evident effect in the latter condition (Table 1) The lesions showed an initial reduction by about 30 to 35% at 24 hours after creation of the lesion. With both mechanical and heptanol lesions a period followed in which the lesion expanded; in the former case to about 80% of the original lesion, while in the latter case to over 110% of the original size. Healing then proceeded in both cases at a slow rate until full healing occurred at 8 days after mechanical, and 10 days after chemical, lesions. Although BAK had no effect on corneal epithelial healing rates, some morphological effects were noted in cells at the edge of the lesions. BAK caused loss of microvilli and some surface cells were also absent; deeper cells were intact. SLS caused more extensive damage with disruption of cells and expansion of the paracellular spaces. By SEM the surface cells appear disrupted and dead but held in place by residual attachments. BAK had no effect on epithelial sucrose permeability after regrowth whereas SLS increased permeability by over 30% (P < 0.01) yDISCUSSIONz The rate of epithelial healing in control corneas was similar to that reported previously (1-3); similarly, the sucrose permeability of the regenerated corneal epithelium found here was similar to that found previously (6). Since BAK induces morphological changes even in normal corneal epithelium (7) and is retained at high concentrations for long times in this membrane (8), it is surprising that no permeability or healing effects were noted in the present study. SLS, however, impeded epithelial regrowth with an initial partial covering of the lesion followed by an expansion to an area even greater than the initial lesion size at 42 hours after an n-heptanol lesion. These changes could be related to changes in protein profiles seen in ocular cells after exposure to SLS (9). This effect in regrowing cells resembles the effect seen in cells growing in tissue culture. SLS may alter the protein metabolism to a catabolic state in growing cells to account for the expansion of the lesion. No other agents tested altered epithelial healing rates after mechanical lesions. Some other studies have indicated that thimerosal and chlorhexidine digluconate delay corneal epithelial healing; the difference between those studies and the present study may relate to the presence of to the ingredients in the test solutions used earlier (10).