The effects of combination glaucoma medications on ocular surface epithelial cells

The purpose of this study was to determine the effects of two commercially available combination topical ophthalmic medications on human ocular surface cells in vitro. Tissue culture plates (96-well) containing immortalized human corneal and conjunctival epithelial cells were divided into five groups. The test solutions examined were: timolol 0.5%+brimonidine 0.2%, containing 0.0050% benzalkonium chloride (BAK); timolol 0.5%+dorzolamide 2%, containing 0.0075% BAK; and preservative-free artificial tears. Balanced salt solution (BSS) was used as the live control, and a fixative solution containing 70% methanol and 0.2% saponin was used as the dead control. Cells were exposed to 100 mu L of test or control solution for 25 minutes at 37A degrees C and 5% carbon dioxide (CO2). A live cell assay was used to measure the toxicity of combination treatments compared with BSS controls. Exposure to timolol 0.5%+brimonidine 0.2% resulted in a significantly higher percentage of living conjunctival cells (48%+/- 12%) as compared with timolol 0.5%+dorzolamide 2% (10%+/- 5%, P < 0.00001). In corneal cells, testing revealed 12%+/- 3% live cells after timolol 0.5%+brimonidine 0.2% exposure compared with 2%+/- 3% after timolol 0.5%+dorzolamide 2% (P < 0.001). Both combination medications demonstrated a significant reduction in the percentage of live corneal and conjunctival epithelial cells compared with control. However, cell cultures exposed to timolol 0.5%+dorzolamide 2% had significantly fewer live cells compared with cell cultures exposed to timolol 0.5%+brimonidine 0.2%. Further studies are needed to better understand the clinical significance of these findings in patients using these medications for chronic treatment of glaucoma and ocular hypertension.