Permeation into but not across the cornea: Bioimaging of intact nanoemulsions and nanosuspensions using aggregation-caused quenching probes

Nanoemulsions and nanosuspensions are two representative nanoparticles with great potential to enhance ocular bioavailability. However, they can permeate into but not across the cornea. The cargo molecules can reach the anterior chamber or back of the eye by diffusing across the cornea and through the conjunctiva-scleral route, respectively. [Display omitted] Nanoemulsions (NEs) and nanosuspensions (NSs) show great potential in enhancing the ocular bioavailability of therapeutics through topical delivery. However, transocular fate of intact NEs and NSs is still inconclusive. In this study, an aggregation-caused quenching fluorescent probe is used to track precorneal retention and transocular transportation of intact NEs and NSs, while coumarin 6 is used to mimick the cargo. NEs show superior precorneal retention to NSs. Both the two types of nanocarriers can permeate into but not across the cornea. The smaller NEs (100 nm) permeate better into the cornea than the bigger ones (210 nm). Nanocarriers in the cornea serves as depots. The released cargo molecules can penetrate across the cornea and diffuse into the lens. Moreover, the conjunctiva-scleral route may be potential to deliver drugs to the back of the eye. In conclusion, the study provides useful tools and information in the field of transocular transportation of nanoparticles.