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**23**

**Chapter 2**

*and Jane H. Hsiao*

ing the vitreous cavity and the retina.

novel drug delivery system

**1. Introduction and objective**

**Abstract**

Breaking down the Barrier: Topical

Liposomes as Nanocarriers for

*José Navarro-Partida, Alejandro González-De la Rosa* 

Topical instillation is the most widely preferred noninvasive route of drug administration to treat diseases affecting the anterior segment of the eye. Nonetheless, the ocular bioavailability for deeper ocular tissues is very low. Different routes of administration, such as intravitreal injections, periocular injections, and systemic administration, have been used to deliver drugs into the posterior segment ocular tissues. However, the presence of blood-retinal barriers (BRBs) makes systemic administration an impractical approach, whereas the drug delivery with the periocular administration route is compromised by ocular static and dynamic barriers. On the other hand, intravitreal injection, the most common and widely recommended route for drug administration to treat posterior ocular diseases, is related to several side effects such as endophthalmitis, hemorrhage, retinal detachment, and poor patient tolerance. Diverse strategies to overcome ocular barriers have been explored for topical drop formulations in order to deliver drugs into the posterior segment ocular tissues. In this chapter, we will review the promising topical nanocarriers for drug delivery into the posterior segment of the eye, emphasizing the use of liposomes for topical ophthalmic formulations target-

**Keywords:** liposomes, retina, vitreous, ocular posterior segment, nanocarriers,

The eyeball may be divided into two parts: the anterior and the posterior segments. The anterior segment consists of the pupil, cornea, iris, ciliary body, aqueous humor, and lens, whereas the posterior segment is comprised of the vitreous humor, macula, retina, choroid, and optic nerve. The retina is the sensitive layer which creates nerve impulses that are transmitted through the optic nerve to the brain. The macula is a specialized area of the retina that is responsible for the central, high-resolution color vision [1]. The retina and macula can suffer from

Segment of the Eyeball

*Arturo Santos, Juan C. Altamirano-Vallejo,* 

Drug Delivery into the Posterior
