Ocular Drug Delivery: a Comprehensive Review

Abstract

The human eye is a sophisticated organ with distinctive anatomy and physiology that hinders the passage of drugs into targeted ophthalmic sites. Effective topical administration is an interest of scientists for many decades. Their difficult mission is to prolong drug residence time and guarantee an appropriate ocular permeation. Several ocular obstacles oppose effective drug delivery such as precorneal, corneal, and blood-corneal barriers. Routes for ocular delivery include topical, intravitreal, intraocular, juxtascleral, subconjunctival, intracameral, and retrobulbar. More than 95% of marketed products exists in liquid state. However, other products could be in semi-solid (ointments and gels), solid state (powder, insert and lens), or mixed (in situ gel). Nowadays, attractiveness to nanotechnology-based carries is resulted from their capabilities to entrap both hydrophilic and lipophilic drugs, enhance ocular permeability, sustain residence time, improve drug stability, and augment bioavailability. Different in vitro, ex vivo, and in vivo characterization approaches help to predict the outcomes of the constructed nanocarriers. This review aims to clarify anatomy of the eye, various ocular diseases, and obstacles to ocular delivery. Moreover, it studies the advantages and drawbacks of different ocular routes of administration and dosage forms. This review also discusses different nanostructured platforms and their characterization approaches. Strategies to enhance ocular bioavailability are also explained. Finally, recent advances in ocular delivery are described. Graphical Abstract

Role of Polymeric Micelles in Ocular Drug Delivery: An Overview of Decades of Research

“…Figure 2 summarizes different systems used for this purpose under two general categories of ocular delivery systems: topical and injectable ocular dosage forms. 54 300 to 450 rabbit model of uveitis showed reduced symptoms with micelles prepared from triblock copolymer cross-linked via MBA (Micelle-MBA) as compared to triblock copolymer cross-linked with TEGDMA (Micelle-TG). the micelles-TG showed higher anti-inflammatory activity based on Hogan's score for a longer duration compared to aqueous suspension of the drug as well as the simple dexamethasone eye drop available in the market.tThe topical application of the micelle-TG showed significant reductions in the Hogan's score (1.17 ± 0. contains both hydrophilic (polar) and hydrophobic (nonpolar) ends.…”

“…An ideal ocular dosage form can deliver the desired concentration of the drug to the affected area of the eye consistently and reliably while being compliant with patient needs to encourage adherence to medication use. Figure summarizes different systems used for this purpose under two general categories of ocular delivery systems: topical and injectable ocular dosage forms. , …”

A recent overview of surfactant–drug interactions and their importance

“…Drug precipitation can take place in two stages: crystal development and nucleation. 104 There are several ways to prevent precipitation, including the use of polymers, the inclusion of surfactants, adjusting drug loading and solubilising capacity, altering the environment's pH, etc. 105 Nanotechnology-based carriers' capacity to entrap both hydrophilic and lipophilic medicines, improve ocular permeability, prolong residence duration, enhance drug stability, and increase bioavailability is the reason for their development.…”

Advances in Nanogels for Topical Drug Delivery in Ocular Diseases

“…The problem with suspensions is that they are unstable by nature, and the crystal structure of that structure could change if placed somewhere for a while. This could alter particle size, thus affecting their solubility by either increasing or decreasing it [ 10 ]. Moreover, increased tear secretion and rapid drug drainage from the individual’s ocular surface due to ocular irritation by the presence of particles > 10 μm in solution greatly reduced the bioavailability [ 11 ].…”