Table 1.

General ocular drug delivery systems available for pharmaceutical application.

Classification	Types	General Description
Conventional systems	Topical liquid/solution eye drop	Immediately active Concentration rapidly decline after administration, following first order kinetics Various additives added: viscosity enhancers, permeation enhancers & cyclodextrins
	Emulsion	Improvement in solubility & bioavailability Oil in water (o/w), water in oil (w/o) systems commercially exploited as vehicles for active pharmaceuticals o/w is common & widely preferred over w/o system. o/w has less irritation and better ocular tolerance
	Suspension	Dispersion of finely divided insoluble API in an aqueous solvent Suspension particles retain in precorneal pocket and improve drug contact time and duration of action relative to drug solution Dysgeusia, ocular irritation, nasopharyngitis adverse events were observed
	Ointment	Mixture of semisolid & solid hydrocarbon (paraffin) that has melting point at physiological ocular temperature (34 °C) Ointments help to improve ocular bioavailability and sustain the drug release
Nano-Technology based systems	Nanomicelle	Most commonly used carrier systems to form API in to clear aqueous solutions Amphiphilic molecules like surfactants or polymer are used to form nanomicelle High drug encapsulation capability, ease of preparation, small size, hydrophilic nanomicellar corona forming aqueous solution Micellar formulation enhance bioavailability of API in ocular tissues
	Nanoparticle	Colloidal carrieres containing size range of 10–1000 nm Nanoparticles can form nanocapsules or nanospheres Small size, leading to low irritation and sustained release property avoiding frequent administration
	Nanosuspension	Colloidal dispersion of submicron drug particles stabilized by polymers or surfactants Sterilization advantages, ease of eye drop formulation, less irritation, precorneal residence time increase and enhancement in ocular bioavailability for drugs insoluble in tear fluid.