Over the past decade, there has been a rise in the number of clinical cases of moderate to severe anterior segment ocular diseases. Conventional topical ophthalmic formulations have several limitations-to address which, novel...
moreOver the past decade, there has been a rise in the number of clinical cases of moderate to severe anterior segment ocular diseases. Conventional topical ophthalmic formulations have several limitations-to address which, novel drug-delivery systems are needed. Additionally, formidable physiological barriers limit ocular bioavailability through the topical route of application. During the last decade, various nano-scaled ocular drug-delivery strategies have been reported. Some of these exploratory, topical, noninvasive approaches have shown promise in improving penetration into the anterior segment tissues of the eye. In this article, we review the available literature with respect to the safety, efficiency and effectiveness of these nano systems. Ocular drug delivery has remained a challenging task for pharmaceutical scientists. This, coupled with the aging population and manifestation of other age-related diseases, explains why the National Eye Institute has predicted a significant rise in clinical cases involving diseases affecting the ocular segments, across various age and ethnic groups [1]. This review focuses on the rising use of noninvasive nanotechnology to improve the therapeutic outcomes in diseases affecting the anterior segment of the eye. The frequently encountered sight-threatening anterior segment ocular diseases are cataract, glaucoma, keratitis, ocular hypertension and uveitis [2-5]. According to the National Eye Institute and the WHO, cataract is one of the major causes of blindness, accounting for 51% of the blindness worldwide [1,6-8]. Topical administration, a localized noninvasive technique, is the most preferred route of dosing for anterior segment ocular diseases. The topical route, however, is associated with low ocular bioavailability (<5% of the administered dose) because of various physiological and mechanical barriers [5]. Conventional topical ophthalmic formulations include eye drops (solutions, suspensions) and ointments. Some emulsion formulations are also currently in the market (Restasis R , Cationorm R). Limited retention on the ocular surface and the need for the drug candidate to possess ideal physicochemical characteristics, to facilitate efficient penetration through the complex ocular structures, however, limits the efficiency of these dosage forms [9]. Solutions are rapidly drained from the conjunctival cul-de-sac allowing very little time for the drug to partition into the ocular tissues. Moreover, the instilled drop size must be in the range of 25-50 μl, which does not allow for the development of a high concentration gradient across the ocular tissues and demands good solubility characteristics, especially at the pH of the tear fluids. To improve the efficacy of the topical ophthalmic solutions or suspensions, high viscosity (thixotropic or shear thinning) solutions and hydrogels, have been developed to increase retention on the ocular surface [10]. Moreover, in contrast to solutions, suspension formulations are better retained on the ocular surface because of the deposition of the drug particles in the conjunctival cul-de-sac. Suspensions are also the primary choice for compounds with poor aqueous solubility (in relation to the target dose). Compared with solutions and suspensions, ointments are not commonly used for conditions affecting the eye because of the oily components that affect vision for some time Ther. Deliv. (2018) 9(2), 137-153