Nanotechnology for Topical Drug Delivery to the Anterior Segment of the Eye

Abstract

Topical drug delivery is one of the most challenging aspects of eye therapy. Eye drops are the most prevalent drug form, especially for widely distributed anterior segment eye diseases (cataracts, glaucoma, dry eye syndrome, inflammatory diseases, etc.), because they are convenient and easy to apply by patients. However, conventional drug formulations are usually characterized by short retention time in the tear film, insufficient contact with epithelium, fast elimination, and difficulties in overcoming ocular tissue barriers. Not more than 5% of the total drug dose administered in eye drops reaches the interior ocular tissues. To overcome the ocular drug delivery barriers and improve drug bioavailability, various conventional and novel drug delivery systems have been developed. Among these, nanosize carriers are the most attractive. The review is focused on the different drug carriers, such as synthetic and natural polymers, as well as inorganic carriers, with special attention to nanoparticles and nanomicelles. Studies in vitro and in vivo have demonstrated that new formulations could help to improve the bioavailability of the drugs, provide sustained drug release, enhance and prolong their therapeutic action. Promising results were obtained with drug-loaded nanoparticles included in in situ gel.

Keywords: anterior segment of the eye; in situ gels; nanomicelles; nanoparticles; ocular barriers; ocular drug delivery.

Figure 1

The scheme of the eye. The ocular globe can be conditionally divided into two parts: the anterior segment and the posterior segment. The anterior eye segment consists of the cornea, conjunctiva, iris, ciliary body, lens, and aqueous humor, while the sclera, choroid, retina, and vitreous body form the posterior segment. Created with BioRender.com.

Figure 2

Schematic representation of the structure and composition of the cornea and the tear film. The cornea consists of the tear film, epithelium, Bowman’s membrane, stroma, Descemet’s membrane, and inner endothelium. The tear film consists of the outer lipid phase, intermediate aqueous phase, and mucus. Created with BioRender.com.

Figure 3

Schematic representation of ocular drug delivery systems for topical administration. Recently FDA approved and developed ocular drug systems presented. Created with BioRender.com.

Figure 4

Schematic presentation of the advantages of the use of nanoformulations of ophthalmic drugs. Created with BioRender.com.