Anterior eye segment drug delivery systems: current treatments and future challenges

Drug delivery strategies to improve the treatment of corneal disorders

Anterior eye disorders including dry eye syndrome, keratitis, chemical burns, and trauma have varying prevalence rates in the world. Classical dosage forms based-topical ophthalmic drugs are popular treatments for managing corneal diseases. However, current dosage forms of ocular drugs can be associated with major challenges such as the short retention time in the presence of ocular barriers. Developing alternative therapeutic methods is required to overcome drug bioavailability from ocular barriers. Nanocarriers are major platforms and promising candidates for the administration of ophthalmic drugs in an adjustable manner. This paper briefly introduces the advantages, disadvantages, and characteristics of delivery systems for the treatment of corneal diseases. Additionally, advanced technologies such as 3D printing are being considered to fabricate ocular drug carriers and determine drug dosages for personalized treatment. This comprehensive review is gathered through multiple databases such as Google Scholar, PubMed, and Web of Science. It explores information around "ocular drug delivery systems'', "nano-based drug delivery systems'', "engineered nanocarriers'', and "advanced technologies to fabricate personalized drug delivery systems''.

Healing the cornea: Exploring the therapeutic solutions offered by MSCs and MSC-derived EVs

Affecting a large proportion of the population worldwide, corneal disorders constitute a concerning health hazard associated to compromised eyesight or blindness for most severe cases. In the last decades, mesenchymal stem/stromal cells (MSCs) demonstrated promising abilities in improving symptoms associated to corneal diseases or alleviating these affections, especially through their anti-inflammatory, immunomodulatory and pro-regenerative properties. More recently, MSC therapeutic potential was shown to be mediated by the molecules they release, and particularly by their extracellular vesicles (EVs; MSC-EVs). Consequently, using MSC-EVs emerged as a pioneering strategy to mitigate the risks related to cell therapy while providing MSC therapeutic benefits. Despite the promises given by MSC- and MSC-EV-based approaches, many improvements are considered to optimize the therapeutic significance of these therapies. This review aspires to provide a comprehensive and detailed overview of current knowledge on corneal therapies involving MSCs and MSC-EVs, the strategies currently under evaluation, and the gaps remaining to be addressed for clinical implementation. From encapsulating MSCs or their EVs into biomaterials to enhance the ocular retention time to loading MSC-EVs with therapeutic drugs, a wide range of ground-breaking strategies are currently contemplated to lead to the safest and most effective treatments. Promising research initiatives also include diverse gene therapies and the targeting of specific cell types through the modification of the EV surface, paving the way for future therapeutic innovations. As one of the most important challenges, MSC-EV large-scale production strategies are extensively investigated and offer a wide array of possibilities to meet the needs of clinical applications.

Recent updates on drug delivery approaches for improved ocular delivery with an insight into nanostructured drug delivery carriers for anterior and posterior segment disorders

Ocular diseases have a major impact on patient's vision and quality of life, with approximately 2.2 billion people have visual impairment worldwide according to the findings from the World Health Organization (WHO). The eye is a complex organ with unique morphology and physiology consisting of numerous ocular barriers which hinders the entry of exogenous substances and impedes drug absorption. This in turn has a substantial impact on effective drug delivery to treat ocular diseases, especially intraocular disorders which has consistently presented a challenge to eye care professionals. The most common method of delivering medications to the eye is topical instillation of eye drops. Although this approach is a viable option for treating many ocular diseases remains a major challenge for the effective treatment of posterior ocular conditions. Up till now, incessant efforts have been committed to design innovative drug delivery systems with the hopes of potential clinical application. Modern developments in nanocarrier's technology present a potential chance to overcome these obstacles by enabling targeted delivery of the loaded medication to the eyes with improved solubility, delayed release, higher penetration and increased retention. This review covers the anatomy of eye with associated ocular barriers, ocular diseases and administration routes. In addition it primarily focuses on the latest progress and contemporary applications of ophthalmic formulations providing specific insight on nanostructured drug delivery carriers reported over the past 5 years highlighting their values in achieving efficient ocular drug delivery to both anterior and posterior segments. Most importantly, we outlined in this review the macro and nanotechnology based ophthalmic drug formulations that are being patented or marketed so far for treating ocular diseases. Finally, based on current trends and therapeutic concepts, we highlighted the challenges faced by novel ocular drug delivery systems and provided prospective future developments for further research in these directions. We hope that this review will serve as a source of motivation and ideas for formulation scientists in improving the design of innovative ophthalmic formulations.

Magnetically Controlled Intraocular Delivery of Dexamethasone Using Silica-Coated Magnetic Nanoparticles

Although the number of patients with eye diseases is increasing, efficient drug delivery to the posterior segment of the eyeball remains challenging. The reasons include the unique anatomy of the eyeball, the blood-aqueous barrier, the blood-retina barrier, and drug elimination via the anterior chamber and uveoscleral routes. Solutions to these obstacles for therapeutic delivery to the posterior segment will increase the efficacy, efficiency, and safety of ophthalmic treatment. Micro/nanorobots are promising tools to deliver therapeutics to the retina under the direction of an external magnetic field. Although many groups have evaluated potential uses of micro/nanorobots in retinal treatment, most experiments have been performed under idealized in vitro laboratory conditions and thus do not fully demonstrate the clinical feasibility of this approach. This study examined the use of magnetic nanoparticles (MNPs) to deliver dexamethasone, a drug widely used in retinal disease treatment. The MNPs allowed sustainable drug release and successful magnetic manipulation inside bovine vitreous humor and the vitreous humor of living rabbits. Therefore, controlled drug distribution via magnetic manipulation of MNPs is a promising strategy for targeted drug delivery to the retina.

Novel nanomicelle butenafine formulation for ocular drug delivery against fungal keratitis: In Vitro and In Vivo study

Fungal keratitis (FK) is a serious infectious corneal disease that leads to blindness. Butenafine (BTF) is an allylamine drug with high antifungal activity, but its poor water solubility and low bioavailability limit its clinical application in ophthalmology. To increase its aqueous solubility and corneal permeability, butenafine was encapsulated in d-ɑ-tocopheryl polyethylene glycol succinate (TPGS) polymeric nanomicelles to improve the bioavailability of the drug for the treatment of FK. Butenafine was successfully fabricated into nanomicelles with a high EE of 96.34 ± 1.65 % and DL of 6.71 ± 0.099 %. The BTF-NM showed an average particle size of 13.12 ± 0.24 nm, a zeta potential of -0.56 ± 0.44 mV and a narrow PDI of 0.12 ± 0.02 with a nearly spherical shape. The characterization results of FTIR, XRD and DSC indicated that BTF was encapsulated in the TPGS nanomicelles. The BTF-NM formulation also showed high storage stability, and the in vitro drug release study showed typical biphasic-release characteristics. In addition, the BTF-NM formulation displayed good cellular tolerance and excellent ocular tolerance in rabbits. Significantly elevated in vitro antifungal activity was also observed in the BTF-NM formulation, and remarkable improvements regarding in vivo corneal permeation were observed compared with the BTF suspension formulation. Finally, the in vivo antifungal activity studies indicated that the BTF-NM formulation had a good therapeutic effect on FK and had similar efficacy to that of commercial natamycin suspension eye drops. These results suggest that the BTF-NM ophthalmic formulation could be a promising ocular drug delivery system for the treatment of FK.

Discovery and Potential Utility of a Novel Non-Invasive Ocular Delivery Platform

To this day, the use of oily eye drops and non-invasive retinal delivery remain a major challenge. Oily eye drops usually cause ocular irritation and interfere with the normal functioning of the eye, while ocular injections for retinal drug delivery cause significant adverse effects and a high burden on the healthcare system. Here, the authors report a novel topical non-invasive ocular delivery platform (NIODP) through the periorbital skin for high-efficiency anterior and posterior ocular delivery in a non-human primate model (NHP). A single dose of about 7 mg JV-MD2 (omega 3 DHA) was delivered via the NIODP and reached the retina at a Cmax of 111 µg/g and the cornea at a Cmax of 66 µg/g. The NIODP also delivered JV-DE1, an anti-inflammatory agent in development for dry eye diseases, as efficiently as eye drops did to the anterior segments of the NHP. The topical NIODP seems to transport drug candidates through the corneal pathway to the anterior and via the conjunctiva/sclera pathway to the posterior segments of the eye. The novel NIODP method has the potential to reshape the landscape of ocular drug delivery. This is especially the case for oily eye drops and retinal delivery, where the success of the treatment lies in the ocular tolerability and bioavailability of drugs in the target tissue.

Sustained release ocular drug delivery systems for glaucoma therapy

INTRODUCTION

Glaucoma is a group of progressive optic neuropathies resulting in irreversible blindness. It is associated with an elevation of intraocular pressure (>21 mm Hg) and optic nerve damage. Reduction of the intraocular pressure (IOP) through the administration of ocular hypotensive eye drops is one of the most common therapeutic strategies. Patient adherence to conventional eye drops remains a major obstacle in preventing glaucoma progression. Additional problems emerge from inadequate patient education as well as local and systemic side effects associated with adminstering ocular hypotensive drugs.

AREAS COVERED

Sustained-release drug delivery systems for glaucoma treatment are classified into extraocular systems including wearable ocular surface devices or multi-use (immediate-release) eye formulations (such as aqueous solutions, gels; ocular inserts, contact lenses, periocular rings, or punctual plugs) and intraocular drug delivery systems (such as intraocular implants, and microspheres for supraciliary drug delivery).

EXPERT OPINION

Sustained release platforms for the delivery of ocular hypotensive drugs (small molecules and biologics) may improve patient adherence and prevent vision loss. Such innovations will only be widely adopted when efficacy and safety has been established through large-scale trials. Sustained release drug delivery can improve glaucoma treatment adherence and reverse/prevent vision deterioration. It is expected that these approaches will improve clinical management and prognosis of glaucoma.

Cyclodextrin-enabled nepafenac eye drops with improved absorption open a new therapeutic window

Nepafenac is a highly effective NSAID used for treating postoperative ocular inflammation and pain after cataract surgery and its advantage over conventional topical NSAIDs has been proved many times. However, Nevanac® is a suspension eye drop, which clearly lacks patient compliance causing irritation, blurred vision, foreign body sensation along with problematic dosage due to its sticky, inhomogeneous consistence. In this study, nepafenac containing eye drops were prepared using hydroxypropyl-β-cyclodextrin to ensure complete dissolution of nepafenac, sodium hyaluronate to provide mucoadhesion and adequate viscosity and a preservative-free officinal formula, Oculogutta Carbomerae containing carbomer (just like Nevanac®), therefore providing a similar base for the new formulations. According to an experimental design, 11 formulations were tested in vitro including two reference formulations by measuring their viscosity, mucoadhesion, drug release and corneal permeability. Finally, two formulations were found promising and investigated further on porcine eyes ex vivo and corneal distribution of nepafenac was determined by RAMAN mapping. The results showed that one formulation possessed better bioavailability ex vivo than Nevanac® 0.1 % suspension, while the other formulation containing only 60 % of the original dose were ex vivo equivalent with Nevanac® opening the way to nepafenac-containing eye drops with better patient compliance in the future.

Delivery Systems in Ocular Retinopathies: The Promising Future of Intravitreal Hydrogels as Sustained-Release Scaffolds

Slow-release delivery systems are needed to ensure long-term sustained treatments for retinal diseases such as age-related macular degeneration and diabetic retinopathy, which are currently treated with anti-angiogenic agents that require frequent intraocular injections. These can cause serious co-morbidities for the patients and are far from providing the adequate drug/protein release rates and required pharmacokinetics to sustain prolonged efficacy. This review focuses on the use of hydrogels, particularly on temperature-responsive hydrogels as delivery vehicles for the intravitreal injection of retinal therapies, their advantages and disadvantages for intraocular administration, and the current advances in their use to treat retinal diseases.

Advances in drug therapy and delivery for cataract treatment

PURPOSE OF REVIEW

Cataract is one of the leading causes of blindness worldwide and surgery is the only available treatment. Pharmacological therapy has emerged as a potential approach to combat the global shortage of surgery due to a lack of access and resources. This review summarizes recent findings in pharmacological treatment and delivery, focusing on drugs that target oxidative stress and the aggregation of crystallins.

RECENT FINDINGS

Antioxidants and oxysterols have been shown to improve or reverse lens opacity in cataract models. N-acetylcysteine amide and N-acetylcarnosine are two compounds that have increased bioavailability over their precursors, alleviating the challenges that have come with topical administration. Studies have shown promising results, with topical N-acetylcarnosine clinically decreasing lens opacity. Furthermore, lanosterol, and more recently 5-cholesten-3b,25-diol (VP1-001), have been reported to combat the aggregation of crystallins in vivo and ex vivo . Delivery has improved with the use of nanotechnology, but further research is needed to solidify these compounds' therapeutic effects on cataracts and improve delivery methods to the lens.

SUMMARY

Although further research in drug dosage, delivery, and mechanisms will need to be conducted, pharmacologic therapies have provided new strategies and treatments for the reversal of cataracts.

Engineering Advanced Drug Delivery Systems for Dry Eye: A Review

Dry eye disease (DED) is a widespread and frequently reported multifactorial ocular disease that not only causes ocular discomfort but also damages the cornea and conjunctiva. At present, topical administration is the most common treatment modality for DED. Due to the existence of multiple biological barriers, instilled drugs generally exhibit short action times and poor penetration on the ocular surface. To resolve these issues, several advanced drug delivery systems have been proposed. This review discusses new dosage forms of drugs for the treatment of DED in terms of their characteristics and advantages. Innovative formulations that are currently available in the market and under clinical investigation are elaborated. Meanwhile, their deficiencies are discussed. It is envisioned that the flourishing of advanced drug delivery systems will lead to improved management of DED in the near future.

Parametric Drug Release Optimization of Anti-Inflammatory Drugs by Gold Nanoparticles for Topically Applied Ocular Therapy

Eye drops represent 90% of all currently used ophthalmic treatments. Only 0.02% of therapeutic molecules contained in eye drops reach the eye anterior chamber despite their high concentration. The tear film efficiently protects the cornea, reducing access to the target. Thereby, the increase in the drug bioavailability and efficiency must come from the mucoadhesion optimization of the drug delivery system. The gold nanoparticles, used as a drug delivery system in this study, already showcased ultrastable and mucoadhesive properties. The goal was to study the gold nanoparticles' ability to release two specific ophthalmic drugs, flurbiprofen and ketorolac. The parameters of interest were those involving the loading conditions, the gold nanoparticles properties, and the release experimental conditions. The drug release was measured using an in vitro model based on dialysis bags coupled with UV-visible spectroscopy. Gold nanoparticles showed an ability to release different molecules, whether hydrophobic or hydrophilic, in passive or active drug release environments. Based on these preliminary results, gold nanoparticles could represent a promising drug delivery system for ketorolac and flurbiprofen when topically applied through eye drops.

PLGA-Based Nanomedicine: History of Advancement and Development in Clinical Applications of Multiple Diseases

Research on the use of biodegradable polymers for drug delivery has been ongoing since they were first used as bioresorbable surgical devices in the 1980s. For tissue engineering and drug delivery, biodegradable polymer poly-lactic-co-glycolic acid (PLGA) has shown enormous promise among all biomaterials. PLGA are a family of FDA-approved biodegradable polymers that are physically strong and highly biocompatible and have been extensively studied as delivery vehicles of drugs, proteins, and macromolecules such as DNA and RNA. PLGA has a wide range of erosion times and mechanical properties that can be modified. Many innovative platforms have been widely studied and created for the development of methods for the controlled delivery of PLGA. In this paper, the various manufacturing processes and characteristics that impact their breakdown and drug release are explored in depth. Besides different PLGA-based nanoparticles, preclinical and clinical applications for different diseases and the PLGA platform types and their scale-up issues will be discussed.

Preparation and in vitro and in vivo evaluation of an isoliquiritigenin-loaded ophthalmic nanoemulsion for the treatment of corneal neovascularization

Isoliquiritigenin (ISL), as a natural flavonoid, has been proven to have therapeutic potential for corneal neovascularization (CNV) treatment; however, its therapeutic use is restricted due to its poor aqueous solubility and limited bioavailability. To overcome these limitations, a novel ISL-loaded nanoemulsion (ISL-NE) was designed for inhibiting CNV in this study. ISL-NE formulation was composed of propylene glycol dicaprylate (PGD), Cremophor® EL (EL35), polyethylene glycol 400 (PEG 400) and adding water with sodium hyaluronate, its particle size was 34.56 ± 0.80 nm with a low polydispersity index of less than 0.05, which suggested a narrow size distribution. The results demonstrated that ISL-NE released higher and permeated more drug than ISL suspension (ISL-Susp) in in vitro drug release and ex vivo corneal permeation study. ISL-NE showed no cytotoxicity in human corneal epithelial cells toxicity study, which was consistent with the result of ocular irritation study in rabbit eyes. ISL-NE had bioavailability 5.76-fold, 7.80-fold and 2.13-fold higher than ISL-Sups in tears, cornea and aqueous humor after a single dose of ISL-NE, respectively. Furthermore, the efficacy of ISL-NE treatment (0.2% ISL) was comparable to that of dexamethasone treatment (0.025%) in the inhibition of CNV in mice model. Enzyme-linked immunosorbent assay (ELISA) showed that the expressions of corneal vascular endothelial growth factor (VEGF-A) and matrix metalloproteinase (MMP-2) were decreased. In conclusion, the ISL-NE demonstrated excellent physicochemical properties, good tolerance, and enhanced ocular bioavailability. It could be a promising, safe, and effective treatment for CNV.

Ocular Drug Delivery: Advancements and Innovations

Ocular drug delivery has been significantly advanced for not only pharmaceutical compounds, such as steroids, nonsteroidal anti-inflammatory drugs, immune modulators, antibiotics, and so forth, but also for the rapidly progressed gene therapy products. For conventional non-gene therapy drugs, appropriate surgical approaches and releasing systems are the main deliberation to achieve adequate treatment outcomes, whereas the scope of “drug delivery” for gene therapy drugs further expands to transgene construct optimization, vector selection, and vector engineering. The eye is the particularly well-suited organ as the gene therapy target, owing to multiple advantages. In this review, we will delve into three main aspects of ocular drug delivery for both conventional drugs and adeno-associated virus (AAV)-based gene therapy products: (1) the development of AAV vector systems for ocular gene therapy, (2) the innovative carriers of medication, and (3) administration routes progression.

Therapeutic Ultrasound for Topical Corneal Delivery of Macromolecules

Purpose

The objective of this study was to utilize therapeutic ultrasound in enhancing delivery of topical macromolecules into the cornea.

Methods

Rabbit corneas were dissected and placed in a diffusion cell with a small ultra-red fluorescent protein (smURFP; molecular weight of 32,000 Da) as a macromolecule solution. The corneas were treated with continuous ultrasound application at frequencies of 400 or 600 kHz and intensities of 0.8 to 1.0 W/cm2 for 5 minutes, or sham-treated. Fluorescence imaging of the cornea sections was used to observe the delivery of macromolecules into individual epithelial cells. Spectrophotometric analysis at smURFP maximal absorbance of 640 nm was done to determine the presence of macromolecules in the receiver compartment. Safety of ultrasound application was studied through histology analysis.

Results

Ultrasound-treated corneas showed smURFP delivery into epithelial cells by fluorescence in the cytoplasm, whereas sham-treated corneas lacked any appreciable fluorescence in the individual cells. The sham group showed 0% of subcellular penetration, whereas the 400 kHz ultrasound-treated group and 600 kHz ultrasound-treated group showed 31% and 57% of subcellular penetration, respectively. Spectrophotometry measurements indicated negligible presence of smURFP macromolecules in the receiver compartment solution in both the sham and ultrasound treatment groups, and these macromolecules did not cross the entire depth of the cornea. Histological studies showed no significant corneal damage due to ultrasound application.

Conclusions

Therapeutic ultrasound application was shown to increase the delivery of smURFP macromolecules into the cornea.

Translational Relevance

Our study offers a clinical potential for a minimally invasive macromolecular treatment of corneal diseases.

The Use of Polymer Blends in the Treatment of Ocular Diseases

The eye is an organ with limited drug access due to its anatomical and physiological barriers, and the usual forms of ocular administration are limited in terms of drug penetration, residence time, and bioavailability, as well as low patient compliance. Hence, therapeutic innovations in new drug delivery systems (DDS) have been widely explored since they show numerous advantages over conventional methods, besides delivering the content to the eye without interfering with its normal functioning. Polymers are usually used in DDS and many of them are applicable to ophthalmic use, especially biodegradable ones. Even so, it can be a hard task to find a singular polymer with all the desirable properties to deliver the best performance, and combining two or more polymers in a blend has proven to be more convenient, efficient, and cost-effective. This review was carried out to assess the use of polymer blends as DDS. The search conducted in the databases of Pubmed and Scopus for specific terms revealed that although the physical combination of polymers is largely applied, the term polymer blend still has low compliance.

Light-responsive biomaterials for ocular drug delivery

Light-responsive biomaterials can be used for the delivery of therapeutic drugs and nucleic acids, where the tunable/precise delivery of payload highlights the potential of such biomaterials for treating a variety of conditions. The translucency of eyes and advances of laser technology in ophthalmology make light-responsive delivery of drugs feasible. Importantly, light can be applied in a non-invasive fashion; therefore, light-triggered drug delivery systems have great potential for clinical impact. This review will examine various types of light-responsive polymers and the chemistry that underpins their application as ophthalmic drug delivery systems.

Evaluation of Topical and Subconjunctival Injection of Hyaluronic Acid-Coated Nanoparticles for Drug Delivery to Posterior Eye

Posterior eye diseases, such as age-related macular degeneration and diabetic retinopathy, are difficult to treat due to ineffective drug delivery to affected areas. Intravitreal injection is the primary method for posterior eye drug delivery; however, it is usually accompanied by complications. Therefore, an effective and non-invasive method is required. Self-assembling nanoparticles (NPs) made from gelatin-epigallocatechin gallate (EGCG) were synthesized (GE) and surface-decorated with hyaluronic acid (HA) for drug delivery to the retinal/choroidal area. Different HA concentrations were used to prepare NPs with negative (GEH-) or positive (GEH+) surface charges. The size/zeta potential and morphology of the NPs were characterized by a dynamic light scattering (DLS) system and transmission electron microscope (TEM). The size/zeta potential of GEH+ NPs was 253.4 nm and 9.2 mV. The GEH- NPs were 390.0 nm and -35.9 mV, respectively. The cytotoxicity was tested by adult human retinal pigment epithelial cells (ARPE-19), with the results revealing that variant NPs were non-toxicity at 0.2-50 µg/mL of EGCG, and that the highest amount of GEH+ NPs was accumulated in cells examined by flowcytometry. Topical delivery (eye drops) and subconjunctival injection (SCI) methods were used to evaluate the efficiency of NP delivery to the posterior eyes in a mouse model. Whole eyeball cryosections were used to trace the location of fluorescent NPs in the eyes. The area of fluorescent signal obtained in the posterior eyes treated with GEH+ NPs in both methods (eye drops: 6.89% and SCI: 14.55%) was the greatest when compared with other groups, especially higher than free dye solution (2.79%). In summary, GEH+ NPs can be transported to the retina by eye drops and SCI; in particular, eye drops are a noninvasive method. Furthermore, GEH+ NPs, characterized by a positive surface and HA decoration, could facilitate drug delivery to the posterior eye as a useful drug carrier.

New Preservative-Free Formulation for the Enhanced Ocular Bioavailability of Prostaglandin Analogues in Glaucoma

Glaucoma is a wide-spread eye disease caused by elevated intraocular pressure. Uncontrolled, this pressure may lead to damages to the optic nerve. Prostaglandin analogues, such as latanoprost and travoprost (which are water-insoluble active substances), are the most used class of active pharmaceutical ingredient. To administer them as eye drops, preservatives, such as benzalkonium chloride, are used as solubilizers. The latter is known to cause a local inflammation when used chronically and is not recommended for patients with ocular surface disorders. In this work, we sought to use polysorbate 80 (PS80) as a solubilizing agent simultaneously with sodium hyaluronate (NaHA) as a thickener and cytoprotective agent for the corneal surface. The first part of this study assessed the compatibility of the excipients with the active substance, using physicochemical methods such as spectra fluorescence and differential scanning calorimetry (DSC), as well as the solubilization mechanism of PS80 regarding prostaglandin analogues using nuclear magnetic resonance (NMR). The second part evaluated the stability of a formula candidate, its viscosity upon instillation, and its pharmacokinetic profile in rabbits as compared to the commercially approved medicine Travatan®. The results show that sodium hyaluronate is inert with respect to travoprost, while PS80 successfully solubilizes it, meaning that benzalkonium chloride is no longer required. Moreover, the pharmacokinetic profiles of the rabbits showed that the original formula described in the present study enhanced the ocular bioavailability of the drug, making it a promising product to control intraocular pressure with a potential reduced dosage of travoprost, therefore minimizing its related side effects.

Ocular Fluid Mechanics and Drug Delivery: A Review of Mathematical and Computational Models

The human eye is a complex biomechanical structure with a range of biomechanical processes involved in various physiological as well as pathological conditions. Fluid flow inside different domains of the eye is one of the most significant biomechanical processes that tend to perform a wide variety of functions and when combined with other biophysical processes play a crucial role in ocular drug delivery. However, it is quite difficult to comprehend the effect of these processes on drug transport and associated treatment experimentally because of ethical constraints and economic feasibility. Computational modeling on the other hand is an excellent means to understand the associated complexity between these aforementioned processes and drug delivery. A wide range of computational models specific to different types of fluids present in different domains of the eye as well as varying drug delivery modes has been established to understand the fluid flow behavior and drug transport phenomenon in an insilico manner. These computational models have been used as a non-invasive tool to aid ophthalmologists in identifying the challenges associated with a particular drug delivery mode while treating particular eye diseases and to advance the understanding of the biomechanical behavior of the eye. In this regard, the author attempts to summarize the existing computational and mathematical approaches proposed in the last two decades for understanding the fluid mechanics and drug transport associated with different domains of the eye, together with their application to modify the existing treatment processes.

Feasibility of Therapeutic Ultrasound Application in Topical Scleral Delivery of Avastin

Purpose

Macromolecules have been shown to be effective in vision-saving treatments for various ocular diseases, such as age-related macular degeneration and diabetic retinopathy. The current delivery of macromolecules requires frequent intraocular injections and carries a risk of serious adverse effects.

Methods

We tested the application of therapeutic ultrasound as a minimally invasive approach for the delivery of Avastin into the diseased regions of the eye. Avastin (bevacizumab) is an anti-vascular endothelial growth factor (VEGF) antibody with a molecular weight of 149 kDa. We tested the effectiveness and safety of Avastin delivery through rabbit sclera in vitro using a standard diffusion cell model. Ultrasound at frequencies of 400 kHz or 3 MHz with an intensity of 1 W/cm2 was applied for the first 5 minutes of 1-hour drug exposure. Sham treatments mimicked the ultrasound treatments, but ultrasound was not turned on. Absorbance measurements of the receiver compartment solution were performed at 280 nm using a spectrophotometer.

Results

Absorbance measurements indicated no statistical difference between the sham (n = 13) and 400 kHz ultrasound group (n = 15) in the delivery of Avastin through the sclera. However, the absorbance values were statistically different (P < 0.01) between the 3 MHz ultrasound group (0.004, n = 8) and the matched sham group (0.002, n = 7). There was 2.3 times increase in drug delivery in the 3 MHz ultrasound when compared to the corresponding sham group. Histological studies indicated no significant damage in the ultrasound-treated sclera due to ultrasound application.

Conclusions

Our preliminary results provided support that therapeutic ultrasound may be effective in the delivery of Avastin through the sclera.

Translational Relevance

Our study offers clinical potential for a minimally invasive retinopathy treatment.

Drug delivery to the anterior segment of the eye: A review of current and future treatment strategies

Research in the development of ophthalmic drug formulations and innovative technologies over the past few decades has been directed at improving the penetration of medications delivered to the eye. Currently, approximately 90% of all ophthalmic drug formulations (e.g. liposomes, micelles) are applied as eye drops. The major challenge of topical eye drops is low bioavailability, need for frequent instillation due to the short half-life, poor drug solubility, and potential side effects. Recent research has been focused on improving topical drug delivery devices by increasing ocular residence time, overcoming physiological and anatomical barriers, and developing medical devices and drug formulations to increase the duration of action of the active drugs. Researchers have developed innovative technologies and formulations ranging from sub-micron to macroscopic size such as prodrugs, enhancers, mucus-penetrating particles (MPPs), therapeutic contact lenses, and collagen corneal shields. Another approach towards the development of effective topical drug delivery is embedding therapeutic formulations in microdevices designed for sustained release of the active drugs. The goal is to optimize the delivery of ophthalmic medications by achieving high drug concentration with prolonged duration of action that is convenient for patients to administer.

Controlled bimatoprost release from graphene oxide laden contact lenses: In vitro and in vivo studies

Ocular drug delivery using contact lenses may be able to substitute for eye drop therapy. However, issues with hydrophobic drugs (like bimatoprost that is used to treat glaucoma) such as low drug uptake using a simple soaking method into preformed contact lenses and alteration in the swelling and transmittance of lenses restricts the application for drug delivery. This research uses graphene oxide (GO) to control the release of bimatoprost from contact lenses along with improvements in the drug uptake, and lens swelling and transmittance. GO was loaded into silicone hydrogel contact lenses by adding the GO at the same time as lenses were polymerized. These lenses were soaked in bimatoprost. Alternatively contact lenses, either with or without GO, were produced by adding bimatoprost during lens polymerization. GO improved contact lens swelling due to its water binding capacity and lens transmittance due to the molecular dispersion of bimatoprost on the surface of the GO which prevented the local precipitation of the drug. The bimatoprost uptake was not improved in the presence of GO. However, its in vitro release profile was improved. Adding bimatoprost and GO at the same time as lenses were polymerized (DL-GO-BMT) significantly decreased the loss of drug during extraction and sterilization in comparison to contact lenses (DL-BMT) without GO. As the amount of GO was increased, the DL-GO-BMT lenses showed a significant decrease in the burst and cumulative release of bimatoprost. Ocular irritation and histopathology reports demonstrated the safety of GO contact lens. The in vivo pharmacokinetic studies in the rabbit tear fluid showed significant improvement in mean residence time (MRT) and area under the curve (AUC) with DL-GO-0.2 μg-BMT-100 contact lens in comparison to eye drop solution. The study demonstrated that the addition of GO to contact lenses can control the release of bimatoprost as well as improved the lens swelling and transmittance. However, further optimization is needed to modulate the release of drug within the therapeutic level to manage glaucoma.

Characteristics of Chlamydia suis Ocular Infection in Pigs

Chlamydia (C.) suis can often be isolated from conjunctival swab specimens from pigs with conjunctivitis or keratoconjunctivitis. In the field, it is assumed to be a multifactorial disease triggered by immunosuppressing factors. This is the first experimental study to provoke clinical signs of conjunctivitis in pigs after C. suis primary mono-infection. Five six-week-old male piglets, free of ocular chlamydia shedding and seronegative for Chlamydia, were conjunctivally infected with the C. suis-type strain S45 (1 × 10⁹ inclusion forming units), while four piglets served as negative controls. The infection group developed clinical signs of conjunctivitis with a peak in the first week post-infection. Immunohistochemical evaluation revealed the presence of Chlamydia not only in the conjunctival epithelium, but also in the enlarged lacrimal glands, lungs, and intestine. No circulating antibodies could be detected during the whole study period of three weeks, although three different test systems were applied as follows: the complement fixation test, MOMP-based Chlamydiaceae ELISA, and PmpC-based C. suis ELISA. Meanwhile, high numbers of IFN-γ-producing lymphocytes within PBMC were seen after C. suis re-stimulation 14 days post-infection. Hence, these data suggest that entry via the eye may not elicit immunological responses comparable to other routes of chlamydial infections.

Progress in drug formulation design and delivery of medicinal substances used in ophthalmology

Due to the very low bioavailability of drugs administered to the surface of the eyeball, issues related to the formulation of an ophthalmic drug pose a technological challenge. The essence of an ophthalmic drug is the selection of an appropriate active substance (API), but also auxiliary substances that determine the desired drug quality and API availability. The ophthalmic drug is not only classic eye drops. Therefore, on the basis of the literature data, the properties and application of auxiliary substances increasing the pharmaceutical availability of API, improving the penetration of API into the eye structures and modifying the viscosity of eye drops were characterized. The possibility of chemical modification of API and the use of prodrugs in ophthalmic drug forms was also noted. Taking into account the progress in the field of ophthalmic drug formulation, the use of multi-compartment systems (lipid particles, nanoparticles, microparticles, liposomes, niosomes, dendrimers) and modern ophthalmic drug delivery systems (inserts, implants, microneedles, contact lenses, ionophoretic systems) have been indicated. Examples of solutions already used by manufacturers, as well as those in the phase of laboratory or clinical trials, were indicated.

A corneal-PAMPA-based in silico model for predicting corneal permeability

The capability to predict corneal permeability based on physicochemical parameters has always been a desirable objective of ophthalmic drug development. However, previous work has been limited to cases where either the diversity of compounds used was lacking or the performance of the models was poor. Our study provides extensive quantitative structure-property relationship (QSPR) models for corneal permeability predictions. The models involved in vitro corneal permeability measurements of 189 diverse compounds. Preliminary analysis of data showed that there is no significant correlation between corneal-PAMPA (Parallel Artificial Membrane Permeability Assay) permeability values and other pharmacokinetically relevant in silico drug transport parameters like Caco-2, jejunal permeability and blood-brain partition coefficient (logBB). Two different QSPR models were developed: one for corneal permeability and one for corneal membrane retention, based on experimental corneal-PAMPA permeability data. Partial least squares regression was applied for producing the models, which contained classical molecular descriptors and ECFP fingerprints in combination. A complex validation protocol (including internal and external validation) was carried out to provide robust and appropriate predictions for the permeability and membrane retention values. Both models had an overall fit of R² > 0.90, including R²-values not lower than 0.85 for validation runs, and provide quick and accurate predictions of corneal permeability values for a diverse set of compounds.

Borneol: a Promising Monoterpenoid in Enhancing Drug Delivery Across Various Physiological Barriers

Incorporation of permeation enhancers is one of the most widely employed approaches for delivering drugs across biological membranes. Permeation enhancers aid in delivering drugs across various physiological barriers such as brain capillary endothelium, stratum corneum, corneal epithelium, and mucosal membranes that pose resistance to the entry of a majority of drugs. Borneol is a natural, plant-derived, lipophilic, volatile, bicyclic monoterpenoid belonging to the class of camphene. It has been used under the names "Bing Pian" or "Long Nao" in Traditional Chinese Medicine for more than 1000 years. Borneol has been incorporated predominantly as an adjuvant in the traditional Chinese formulations of centrally acting drugs to improve drug delivery to the brain. This background knowledge and anecdotal evidence have led to extensive research in establishing borneol as a permeation enhancer across the blood-brain barrier. Alteration in cell membrane lipid structures and modulation of multiple ATP binding cassette transporters as well as tight junction proteins are the major contributing factors to blood-brain barrier opening functions of borneol. Owing to these mechanisms of altering membrane properties, borneol has also shown promising potential to improve drug delivery across other physiological barriers as well. The current review focuses on the role of borneol as a permeation enhancer across the blood-brain barrier, mucosal barriers including nasal and gastrointestinal linings, transdermal, transcorneal, and blood optic nerve barrier.

Comparative Analysis of Morphological and Release Profiles in Ocular Implants of Acetazolamide Prepared by Electrospinning

The visual impairment that often leads to blindness causes a higher morbidity rate. The goal of this work is to create a novel biodegradable polymeric implant obtained from coaxial fibers containing the dispersed drug-acetazolamide-in order to achieve sustained drug release and increase patient compliance, which is of the highest importance. Firstly, during this work, uncoated implants were produced by electrospinning, and rolled in the shape of small cylinders that were composed of uniaxial and coaxial fibers with immobilized drug inside. The fibers were composed by PCL (poly ε-caprolactone) and Lutrol F127 (poly (oxyethylene-b-oxypropylene-b-oxyethylene)). The prepared implants exhibited a fast rate of drug release, which led to the preparation of new implants incorporating the same formulation but with an additional coating film prepared by solvent casting and comprising PCL and Lutrol F127 or PCL and Luwax EVA 3 ((poly (ethylene-co-vinyl acetate)). Implants were characterized and in vitro release profiles of acetazolamide were obtained in phosphate buffered saline (PBS) at 37 °C. The release profile of the acetazolamide from coated implant containing Luwax EVA 3 is considerably slower than what was observed in case of coated implants containing Lutrol F127, allowing a sustained release and an innovation relatively to other ocular drug delivery systems.

Therapeutic Ophthalmic Lenses: A Review

An increasing incidence of eye diseases has been registered in the last decades in developed countries due to the ageing of population, changes in lifestyle, environmental factors, and the presence of concomitant medical conditions. The increase of public awareness on ocular conditions leads to an early diagnosis and treatment, as well as an increased demand for more effective and minimally invasive solutions for the treatment of both the anterior and posterior segments of the eye. Despite being the most common route of ophthalmic drug administration, eye drops are associated with compliance issues, drug wastage by lacrimation, and low bioavailability due to the ocular barriers. In order to overcome these problems, the design of drug-eluting ophthalmic lenses constitutes a non-invasive and patient-friendly approach for the sustained drug delivery to the eye. Several examples of therapeutic contact lenses and intraocular lenses have been developed, by means of different strategies of drug loading, leading to promising results. This review aims to report the recent advances in the development of therapeutic ophthalmic lenses for the treatment and/or prophylaxis of eye pathologies (i.e., glaucoma, cataract, corneal diseases, or posterior segment diseases) and it gives an overview of the future perspectives and challenges in the field.

Steroid-eluting contact lenses for corneal and intraocular inflammation

Ocular inflammation is one of the leading causes of blindness worldwide, and steroids in topical ophthalmic solutions (e.g. dexamethasone eye drops) are the mainstay of therapy for ocular inflammation. For many non-infectious ocular inflammatory diseases, such as uveitis, eye drops are administered as often as once every hour. The high frequency of administration coupled with the side effects of eye drops leads to poor adherence for patients. Drug-eluting contact lenses have long been sought as a potentially superior alternative for sustained ocular drug delivery; but loading sufficient drug into contact lenses and control the release of the drug is still a challenge. A dexamethasone releasing contact lens (Dex-Lens) was previously developed by encapsulating a dexamethasone-polymer film within the periphery of a hydrogel-based contact lens. Here, we demonstrate safety and efficacy of the Dex-Lens in rabbit models in the treatment of anterior ocular inflammation. The Dex-Lens delivered drug for 7 days in vivo (rabbit model). In an ocular irritation study (Draize test) with Dex-Lens extracts, no adverse events were observed in normal rabbit eyes. Dex-Lenses effectively inhibited suture-induced corneal neovascularization and inflammation for 7 days and lipopolysaccharide-induced anterior uveitis for 5 days. The efficacy of Dex-Lenses was similar to that of hourly-administered dexamethasone eye drops. In the corneal neovascularization study, substantial corneal edema was observed in rabbit eyes that received no treatment and those that wore a vehicle lens as compared to rabbit eyes that wore the Dex-Lens. Throughout these studies, Dex-Lenses were well tolerated and did not exhibit signs of toxicity. Dexamethasone-eluting contact lenses may be an option for the treatment of ocular inflammation and a platform for ocular drug delivery. STATEMENT OF SIGNIFICANCE: Inflammation of the eye can happen either on the ocular surface (i.e. the cornea) or inside the eye, both of which can result in loss of vision or even blindness. Ocular inflammation is normally treated by steroid eye drops. Depending on the type and severity of inflammation, patients may have to take drops every hour for days at a time. Such severe dosing regimen can lead to patients missing doses. Also, more than 95% drug in an eye drop never goes inside the eye. Here we present a contact lens that release a steroid (dexamethasone) for seven days at a time. It is much more efficient than eye drops and a significant improvement since once worn, the patient will avoid missing doses.

Micelles: Promising Ocular Drug Carriers for Anterior and Posterior Segment Diseases

Micelles have been studied in the targeting of drug substances to different tissues as a nano-sized delivery system for many years. Sustained drug release, ease of production, increased solubility, and bioavailability of drugs with low water solubility are the most important superiorites of micellar carriers. These advantages paved the way for the use of micelles as a drug delivery system in the ocular tissues. The unique anatomical structure of the eye as well as its natural barriers and physiology affect ocular bioavailability of the drugs negatively. Conventional dosage forms can only reach the anterior segment of the eye and are used for the treatment of diseases of this segment. In the treatment of posterior segment diseases, conventional dosage forms are administered sclerally, via an intravitreal injection, or systemically. However, ocular irritation, low patient compliance, and high side effects are also observed. Micellar ocular drug delivery systems have significant promise for the treatment of ocular diseases. The potential of micellar systems ocular drug delivery has been demonstrated by in vivo animal experiments and clinical studies, and they are continuing extensively. In this review, the recent research studies, in which the positive outcomes of micelles for ocular targeting of drugs for both anterior and posterior segment diseases as well as glaucoma has been demonstrated by in vitro, ex vivo, or in vivo studies, are highlighted.

Trimethyl chitosan nanoparticles for ocular baicalein delivery: Preparation, optimization, in vitro evaluation, in vivo pharmacokinetic study and molecular dynamics simulation

To improve ocular bioavailability of baicalein (BAI), trimethyl chitosan coated lipid nanoparticles of baicalein (TMC-BAI-LNPs) were prepared, optimized and characterized. The properties of TMC-BAI-LNPs such as morphology, particle size, zeta potential and fourier transform infrared spectroscopy were investigated. Additionally, molecular dynamics simulation was applied as a new method to evaluate drug-biological membrane interactions. Transmission electron microscopy showed that the LNPs were approximately spherical in shape with a smooth surface. TMC-BAI-LNPs had a particle size of 162.8 nm, a positive surface charge with a zeta potential of 26.6 mV. The entrapment efficiency and drug loading values of BAI in the formulation were 90.65% and 2.04%, respectively. Moreover, in vitro drug release revealed that TMC-BAI-LNPs had a sustained release effect. In vivo studies indicated TMC-BAI-LNPs had no ocular irritation and the AUC of TMC-BAI-LNPs was 3.17-fold than that of the control (p < 0.01). Molecular dynamics simulation data showed that BAI had a poor membrane permeability, which limited the ocular bioavailability. The results indicated that TMC-BAI-LNPs might open up a new avenue for ocular administration. Furthermore, molecular dynamics simulation could predict permeability of drugs.

Sustained-release voriconazole-thermogel for subconjunctival injection in horses: ocular toxicity and in-vivo studies

Background

Keratomycosis is a relatively common, sight threatening condition in horses, where treatment is often prolonged and costly. Subconjunctival (SCo) injections offer less resistance to drug diffusion than the topical route, resulting in better penetration to the ocular anterior segment. Voriconazole, a second generation triazole antifungal, is effective against common fungal organisms causing keratomycosis. If combined with a thermogel biomaterial, voriconazole can be easily injected in the SCo space to provide sustained drug release. The purpose of this study was to evaluate the drug concentrations in the anterior segment and clinical effects after SCo injections of voriconazole-containing thermogel: poly (DL-lactide-co-glycolide-b-ethylene glycol-b-DL-lactide-co-glycolide) (PLGA-PEG-PLGA) in healthy equine eyes.

Results

Voriconazole aqueous humor (AH) and tear concentrations were compared between 6 horses, receiving 1% voriconazole applied topically (0.2 mL, q4h) (Vori-Top) or 1.7% voriconazole-thermogel (0.3 mL) injected SCo (Vori-Gel). For the Vori-Gel group, voriconazole concentrations were measured in AH and tears at day 2 and then weekly for 23 days, and at day 2 only for the Vori-Top group. Ocular inflammation was assessed weekly (Vori-Gel) using the modified Hackett-McDonald scoring system. Ocular tissue concentrations of voriconazole following SCo 1.7% voriconazole-thermogel (0.3 mL) injections were evaluated post euthanasia in 6 additional horses at 3 different time points. Three horses received bilateral injections at 2 h (n = 3, right eye (OD)) and 48 h (n = 3, left eye (OS)) prior to euthanasia, and 3 horses were injected unilaterally (OS), 7 days prior to euthanasia. Voriconazole-thermogel was easily injected and well tolerated in all cases, with no major adverse effects. On day 2, drug concentrations in tears were higher in the Vori-Top, but not statistically different from Vori-Gel groups. For the Vori-Gel group, voriconazole was non-quantifiable in the AH at any time point. Total voriconazole concentrations in the cornea were above 0.5 μg/g (the target minimum inhibitory concentration (MIC) for Aspergillus sp.) for up to 48 h; however, concentrations were below this MIC at 7 days post treatment.

Conclusions

Voriconazole-thermogel was easily and safely administered to horses, and provided 48 h of sustained release of voriconazole into the cornea. This drug delivery system warrants further clinical evaluation.

Ophthalmic Drug Delivery Using Iontophoresis: Recent Clinical Applications

Background: Iontophoresis is a noninvasive delivery system designed to overcome barriers to ocular penetration of topical ophthalmic medications by employing a low-amplitude electrical current to promote the migration of a charged drug substance across biological membranes. Trans-scleral iontophoresis of dexamethasone phosphate has demonstrated dramatically increased intraocular concentrations of dexamethasone in rabbit ocular tissues compared with topical instillation, including 50- to 100-fold greater aqueous humor concentrations. Methods: This article reviews available data on recent clinical applications of iontophoretic ophthalmic drug delivery. Results: The EyeGate II delivery system (EGDS) is a trans-scleral iontophoresis system that has been used in conjunction with EGP-437, a proprietary-charged formulation of dexamethasone phosphate for iontophoretic delivery. In patients with noninfectious anterior uveitis, EGP-437, delivered through 2 iontophoretic treatments using the EGDS, demonstrated similar efficacy to topical prednisolone acetate 1% eye drops instilled 8 times daily over 28 days, suggesting the potential to decrease or eliminate the need for daily dosing of topical steroids in this patient population. Other applications for EGP-437 delivered through the EGDS that have been explored in clinical trials include treatment of dry eye, postsurgical inflammation and pain, and scleritis. In addition, transcorneal iontophoresis has been used outside of the United States to enhance riboflavin penetration in patients undergoing corneal cross-linking as therapy for progressive keratoconus. Conclusions: The reviewed studies demonstrate the feasibility of using iontophoresis to enhance drug delivery to ocular tissues and support the potential of this noninvasive technique across a range of ophthalmic indications.

Evaluation of epithelial transport and oxidative stress protection of nanoengineered curcumin derivative-cyclodextrin formulation for ocular delivery

Ocular drug delivery has been a well-known route for the drug administration for the treatment of ocular diseases. However, numerous anatomical and physiological barriers prevailing in the eye itself create considerable challenges for achieving the necessitated therapeutic efficacy along with ocular bioavailability. However, recent advances in nanoengineered strategies hold definite promises in terms of devising improved ophthalmic medicines for the effective drug delivery to target the sites with enhanced ocular bioavailability. Curcumin, a hydrophobic polyphenol yellow colored compound, and its metabolic reduced product, tetrahydrocurcumin (THC), have been known for their beneficial pharmacological functions, such as anti-inflammatory or anti-oxidant activities at various tissue sites. However, the low aqueous solubility of these compounds results in their poor bioavailability, thereby limiting their widespread application. Therefore, in the present study, we investigated the changes in drug solubility by forming inclusion complexes with different derivatives of hydroxypropyl (HP)-cyclodextrins (CD). To this end, the spray drying technique was used for nanoengineering curcumin or THC-loaded formulations to improve the stability of formulations during the storage. The formulations were characterized in terms of physicochemical properties and cellular permeability. The results demonstrated that the encapsulation of curcumin (or THC) into the HP-CDs significantly increased the drug solubility and enhanced the corneal and retinal epithelial permeability. Curcumin or THC complexes in HP-CDs with improved bioavailability also induced anti-oxidant activity (SOD1, CAT1, and HMOX1) in higher levels in the ocular epithelial cells and showed oxidative protection effects in rabbit cornea tissues that will boost up their application in ocular medicine.

Ocular Drug Delivery

Although the eye is an accessible organ for direct drug application, ocular drug delivery remains a major challenge due to multiple barriers within the eye. Key barriers include static barriers imposed by the cornea, conjunctiva, and retinal pigment epithelium and dynamic barriers including tear turnover and blood and lymphatic clearance mechanisms. Systemic administration by oral and parenteral routes is limited by static blood-tissue barriers that include epithelial and endothelial layers, in addition to rapid vascular clearance mechanisms. Together, the static and dynamic barriers limit the rate and extent of drug delivery to the eye. Thus, there is an ongoing need to identify novel delivery systems and approaches to enhance and sustain ocular drug delivery. This chapter summarizes current and recent experimental approaches for drug delivery to the anterior and posterior segments of the eye.

Ocular Drug Delivery: Role of Degradable Polymeric Nanocarriers for Ophthalmic Application

Ocular drug delivery has been a major challenge for clinical pharmacologists and biomaterial scientists due to intricate and unique anatomical and physiological barriers in the eye. The critical requirement varies from anterior and posterior ocular segments from a drug delivery perspective. Recently, many new drugs with special formulations have been introduced for targeted delivery with modified methods and routes of drug administration to improve drug delivery efficacy. Current developments in nanoformulations of drug carrier systems have become a promising attribute to enhance drug retention/permeation and prolong drug release in ocular tissue. Biodegradable polymers have been explored as the base polymers to prepare nanocarriers for encasing existing drugs to enhance the therapeutic effect with better tissue adherence, prolonged drug action, improved bioavailability, decreased toxicity, and targeted delivery in eye. In this review, we summarized recent studies on sustained ocular drug/gene delivery and emphasized on the nanocarriers made by biodegradable polymers such as liposome, poly lactic-co-glycolic acid (PLGA), chitosan, and gelatin. Moreover, we discussed the bio-distribution of these nanocarriers in the ocular tissue and their therapeutic applications in various ocular diseases.

Production and characterization of drug-loaded toroidal vortices from a novel ocular drug delivery device

For the last several decades, the predominant method for delivering medicine to the surface of the eye has been the standard multiuse eye dropper. While being the most popular, this method has significant limitations. Recently, an effort has been made to explore the use of a directed toroidal vortex or "smoke ring" aerosol delivery system that may help overcome these limitations and enable delivery of precise amounts of formulation and drug to the ocular surface. Promising preliminary in vitro studies indicated dosing control, but the physical characteristics of the toriodal aerosol device performance and impaction forces related to patient comfort have yet to be established. Here, we experimentally investigate the mechanics and dynamics of these ocular aerosol vortices, including translational and rotational velocities, spatial droplet size distributions, and relative impaction forces in order to optimize the device performance and evaluate potential for clinical use. Maximal droplet velocity at various actuation forces was determined, and they were found to be all less than 6 m/s even at the highest actuation forces. Moreover, plume impaction forces were determined across a range of conditions and were all less than about 4.5 μN. Collectively, these studies showed that the physical and mechanical properties of the emitted drug-loaded vortices would be suitable for ocular administration.

Recent advances of controlled drug delivery using microfluidic platforms

Conventional systematically-administered drugs distribute evenly throughout the body, get degraded and excreted rapidly while crossing many biological barriers, leaving minimum amounts of the drugs at pathological sites. Controlled drug delivery aims to deliver drugs to the target sites at desired rates and time, thus enhancing the drug efficacy, pharmacokinetics, and bioavailability while maintaining minimal side effects. Due to a number of unique advantages of the recent microfluidic lab-on-a-chip technology, microfluidic lab-on-a-chip has provided unprecedented opportunities for controlled drug delivery. Drugs can be efficiently delivered to the target sites at desired rates in a well-controlled manner by microfluidic platforms via integration, implantation, localization, automation, and precise control of various microdevice parameters. These features accordingly make reproducible, on-demand, and tunable drug delivery become feasible. On-demand self-tuning dynamic drug delivery systems have shown great potential for personalized drug delivery. This review presents an overview of recent advances in controlled drug delivery using microfluidic platforms. The review first briefly introduces microfabrication techniques of microfluidic platforms, followed by detailed descriptions of numerous microfluidic drug delivery systems that have significantly advanced the field of controlled drug delivery. Those microfluidic systems can be separated into four major categories, namely drug carrier-free micro-reservoir-based drug delivery systems, highly integrated carrier-free microfluidic lab-on-a-chip systems, drug carrier-integrated microfluidic systems, and microneedles. Microneedles can be further categorized into five different types, i.e. solid, porous, hollow, coated, and biodegradable microneedles, for controlled transdermal drug delivery. At the end, we discuss current limitations and future prospects of microfluidic platforms for controlled drug delivery.

Drug delivery to the lens for the management of cataracts

Cataracts are one of the most prevalent diseases of the lens, affecting its transparency and are the leading cause of reversible blindness in the world. The clarity of the lens is essential for its normal physiological function of refracting light onto the retina. Currently there is no pharmaceutical treatment for prevention or cure of cataracts and surgery to replace the affected lens remains the gold standard in the management of cataracts. Pharmacological treatment for prevention of cataracts is hindered by many physiological barriers that must be overcome by a therapeutic agent to reach the avascular lens. Various therapeutic agents and formulation strategies are currently being investigated to prevent cataract formation as access to surgery is limited. This review provides a summary of recent research in the field of drug delivery to the lens for the management of cataracts including models used to study cataract treatments and discusses the future perspectives in the field.

Modern Therapeutic Approaches for Noninfectious Ocular Diseases Involving Inflammation

Dry eye disease, age-related macular degeneration, and uveitis are ocular diseases that significantly affect the quality of life of millions of people each year. In these diseases, the action of chemokines, proinflammatory cytokines, and immune cells drives a local inflammatory response that results in ocular tissue damage. Multiple therapeutic strategies are developed to either address the symptoms or abate the underlying cause of these diseases. Herein, the challenges to deliver drugs to the relevant location in the eye for each of these diseases are reviewed along with current and innovative therapeutic approaches that attempt to restore homeostasis within the ocular microenvironment.