Abstract
Purpose: :
To determine the dose - response relationship between benzalkonium chloride (BAC ) topically applied to the ocular surface and the induction of a corneal inflammatory response as quantified by in vivo intravital fluorescence stereomicroscopy.
Methods: :
Recruitment of inflammatory cells was monitored by in vivo fluorescent microscopy and digital photography in Enhanced Green Protein Fluorescently labeled (EGFP) chimeric mice. One eye of each EGFP mouse was topically dosed with a single drop (5µL) of BAC (0.005, 0.01, 0.02, 0.05, 0.1, 0.2 %wt/%vl), where as the contra lateral eye was dosed with saline (control eye). Dosing occurred at days 0, 3, 5, 7, 10 and 15 while under short term anesthesia. In vivo recruitment of EGFP cells was captured at days 1, 3, 5, 7, 10, 15 and 25 and quantification of EGFP cell migration was performed using pixel analysis on digital photos using Image Pro. Corneal haze and scarring was qualitatively evaluated at similar time points.
Results: :
Recruitment of EGFP labeled inflammatory cells was detected in BAC treated corneas with concentrations between 0.05% and 0.2% as early as day 3 and continued to increase in magnitude over the course of the dosing period. This was significantly different from control eyes (p-value <0.001). Similarly, mice treated with lower doses (0.005% to 0.02 %), also displayed significant inflammatory cell recruitment into the cornea, however, the tempo was slower and was not observed until day 10 of treatment (p-value <0.001). In both groups, the magnitude of EGFP cell corneal infiltration correlated with the degree of corneal haze and scarring.
Conclusions: :
Data demonstrate that ocular surface exposure to BAC induces an inflammatory response in a dose - dependent fashion with respect to both tempo and magnitude. Importantly, lower doses of BAC also stimulate the recruitment of inflammatory cells confirming the potentially damaging effects associated with this preservative. This model will help identify the inflammatory signals involved in this process and enable the development of alternative preservatives for use in ophthalmic products.
Keywords: inflammation • cornea: stroma and keratocytes • image processing