“…Drugs applied to the surface of the eye rarely penetrate the ocular surface or enter into the vitreous body and the retina ( Gaudana et al, 2010 ). Biological barriers such as the cornea, conjunctiva and the tear film limit penetration and bioavailability of topical drug preparations to the posterior segment of the eye and therefore direct injection of drugs to the vitreous is commonly used to target drugs to the retina ( Ayalasomayajula and Kompella, 2005; Carneiro et al, 2009; Eldaly and Styles, 2009; Yasukawa et al, 2001 ) but has the risk of significant complications including cataracts, vitreous haemorrhages and retinal detachment. There are several colloidal drug delivery systems such as liposomes ( Hathout et al, 2007; Kaur et al, 2004; Law et al, 2000 ), niosomes ( Abdelbary and El-Gendy, 2008 ), nanoparticles ( Agnihotri and Vavia, 2009 ) and nanoemulsions ( Badawi et al, 2008 ) that enhance bioavailability of drugs to the retina after eye drop administration.…”