Precorneal factors influencing the ocular distribution of topically applied liposomal inulin.

The primary objective of this study was to investigate the effect of several precorneal factors on the retention of liposomes in tears and their interaction with the corneal and conjunctival surfaces. It was found that adsorption of liposomes onto these surfaces was requisite to the ocular absorption of inulin. Over a range of 10 to 50 microliter, the availability of binding sites at the corneal and conjunctival surfaces rather than the size of the instilled volume controlled the extent of liposomal adsorption and ultimately availability of inulin to the intraocular tissues. The inulin liposomes were in facile association with the adsorptive surfaces, as evidenced by their low resistance to removal by rinsing the eye with saline and by the lack of sustained inulin concentrations in any of the ocular tissues studied. This property of liposomes, coupled with the slow rate (1% per hour) at which they released inulin, was responsible for the absence of inulin in the aqueous humor as late as 240 minutes post-dosing. It was concluded that, for liposomes to be effective in ocular drug delivery, they must show affinity for and be bound to the corneal surface and, in addition, must release their contents at optimal rates.