Comparison of the short-term effects on the human corneal surface of topical timolol maleate with and without benzalkonium chloride

PURPOSE: To compare the short-term effects of timolol maleate with and without preservative (0.005% benzalkonium chloride) on pre-corneal tear film stability and corneal epithelial barrier function. SUBJECTS AND METHODS: The study population consisted of 20 healthy volunteers. To obtain baseline values, 7 days before the experiment the non-invasive breakup time of the pre-corneal tear film was measured using a tear specular microscope; corneal fluorescein uptake was measured with a fluorophotometer. Unpreserved or preserved 0.5% timolol was applied to one eye; the contralateral eye was exposed to the other drug. At 30 minutes after instillation, the pre-study tests were repeated. RESULTS: Preserved timolol did, while unpreserved timolol did not, significantly reduce the non-invasive breakup time from the baseline values (baseline and post-exposure values 11.4 and 6.8 seconds, respectively, P = 0.008 for preserved timolol, and 11.7 vs. 11.0 seconds, P = 0.55 for unpreserved timolol). Corneal fluorescein uptake, on the other hand, was significantly increased upon exposure to either preserved or unpreserved timolol (baseline and post-exposure values 37.5 and 82.0 ng/ml, P < 0.001 for preserved timolol, and 35.4 vs. 57.6 ng/ml, P < 0.001 for unpreserved timolol). Preserved timolol exerted the greater effect (P = 0.028). CONCLUSIONS: Exposure to preserved timolol resulted in significant instability in the pre-corneal tear film. Moreover, it disrupted the corneal epithelial barrier function to a greater degree than unpreserved timolol. The elimination of preservatives may be desirable in efforts to protect the integrity of the corneal surface and its interaction with the tear film.