• nanostructured lipid carriers (NLC)
• mucoadhesive excipients
• in situ gelling polymers
• eye drops
• solid lipid nanoparticles (SLN)
• liposomes
• semisolid formulations
• nanocarriers
• microcarriers
• self-emulsifying drug delivery systems
• contact lenses
• ocular inserts

Ocular diseases may be treated via different routes of administration, such as topical, intracameral, intravitreal, oral and parenteral. Among them the topical route is most accepted by patients, although it provides in many cases the lowest bioavailability. Indeed, when a topical formulation reaches the precorneal area, i.e., the drug absorption and/or action site, it is rapidly eliminated away due to eye protection mechanisms such as winking, basal and reflex tearing, and naso-lacrimal draining. To avoid this and to reduce the frequency of dosing, various strategies have been developed to prolong drug residence time instilled on the ocular surface. These strategies include the use of in situ gelling and mucoadhesive excipients as well as combinations thereof. From the drug delivery system point of view, liquid and semisolid formulations are preferred over solid formulations such as ocular inserts and contact lenses. Furthermore, liquid and semisolid formulations can contain nano- and microcarrier systems that contribute to a prolonged residence time. Within this review an overview about the different types of excipients and formulations as well as their performance in valid animal models and clinical trials is provided.
An experimental part will be provided as well. The study focuses on the synthesis and characterization of mucoadhesive thiolated beta cyclodextrins. Furthermore, their mucoadhesiveness and ability to increase the corneal residence time has been studied.