Biopharmaceutics of Ocular Drug Delivery Systems

The eye is a unique organ from an anatomical & physiological point of view. Without the eye, we cannot enjoy the beauty of nature. The eye is a highly specialized organ of photoreception for processing light energy from the environment to produce action potentials in specialized nerve cells, which subsequently relayed to the optic nerve and then to the brain where the information is processed and consciously appreciated as vision. The human eye can be generally divided into the anterior and the posterior segments. The anterior segment includes the cornea, conjunctiva, iris, ciliary body, aqueous humor and lens while the posterior segment comprises sclera, choroid, retina and vitreous humor. The eyeball is an organ protected from exogenous substances and external stress by various barriers, therefore, therapeutic drugs must be transported across several protective barriers regardless of which route administration utilized. The mechanism of ocular drug absorption can be influenced by physiological factors, physicochemical factors & dosage form factors. Physiologically corneal & non corneal drug absorption mechanisms are considered.