Iontophoresis: a non-invasive ocular drug delivery

Spatial targeted delivery of riboflavin with a controlled corneal iontophoresis delivery system in theranostic-guided UV-A light photo-therapy

Seven human donor eye globes underwent corneal cross-linking using theranostic UV-A device with accessory corneal iontophoresis system for patterned delivery of a 0.22% riboflavin solution. Theranostic-guided UV-A light illumination assessed riboflavin distribution and treated corneas at 10 mW/cm2 for 9 min with a 5.0-mm beam size. Corneal topography maps were taken at baseline and 2-h post-treatment. Analysis utilized corneal topography elevation data, with results showing controlled riboflavin delivery led to a consistent gradient, with 40% higher levels centrally (248 ± 79 μg/cm3) than peripherally (180 ± 72 μg/cm3 at ±2.5 mm from the center). Theranostic-guided UV-A light irradiation resulted in significant changes in corneal topography, with a decrease in best-fit sphere value (-0.7 ± 0.2 D; p < 0.001) and consistent downward shift in corneal elevation map (-11.7 ± 3.7 μm). The coefficient of variation was 2.5%, indicating high procedure performance in achieving significant and reliable corneal flattening.

Multi-physics simulations for investigating the effect of electrode conditions on transscleral ocular iontophoresis for particulate drug delivery into ocular tissues

Purpose

Transscleral ocular iontophoresis has been proposed to deliver charged particulate drugs to ocular tissues effectively by transmitting a weak electrical current through the sclera. The electric fields formed are influenced by the electrode conditions, thus affecting the amount of particulate drugs delivered to the ocular tissues via iontophoresis. Computational simulation is widely used to simulate drug concentrations in the eye; therefore, reflecting the characteristics of the drugs in living tissues to the simulations is important for a more precise estimation of drug concentration. In this study, we investigated the effect of electrode conditions (location and size) on the efficacy of transscleral iontophoresis.

Methods

We first determined the simulation parameters based on the comparison of the amount of drug in the sclera in the simulation and in vivo experimental results. The injection of the negatively charged nanoparticles into the cul-de-sac of the lower eyelid was simulated. The active electrode (cathode) was attached to the skin immediately above the injection site, while the return electrode (anode) was placed over the eyebrow. The drug concentration distribution in the eye, based on either the location or size of each electrode, was evaluated using the finite element method with the estimated simulation parameters.

Results

Our results indicate that drug permeability varies depending on the location and the size of the electrodes.

Conclusion

Our findings demonstrate that the determination of optimal electrode conditions is necessary to enhance the effectiveness of transscleral iontophoresis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13534-024-00359-2.

Smart Nanocarriers for the Treatment of Retinal Diseases

Retinal diseases, such as age-related macular degeneration, diabetic retinopathy, and retinoblastoma, stand as the leading causes of irreversible vision impairment and blindness worldwide. Effectively administering drugs for retinal diseases poses a formidable challenge due to the presence of complex ocular barriers and elimination mechanisms. Over time, various approaches have been developed to fabricate drug delivery systems for improving retinal therapy including virus vectors, lipid nanoparticles, and polymers. However, conventional nanocarriers encounter issues related to the controllability, efficiency, and safety in the retina. Therefore, the development of smart nanocarriers for effective or more invasive long-term treatment remains a desirable goal. Recently, approaches have surfaced for the intelligent design of nanocarriers, leveraging specific responses to external or internal triggers and enabling multiple functions for retinal therapy such as topical administration, prolonged drug release, and site-specific drug delivery. This Review provides an overview of prevalent retinal pathologies and related pharmacotherapies to enhance the understanding of retinal diseases. It also surveys recent developments and strategies employed in the intelligent design of nanocarriers for retinal disease. Finally, the challenges of smart nanocarriers in potential clinical retinal therapeutic applications are discussed to inspire the next generation of smart nanocarriers.

Emerging delivery systems based on aqueous two-phase systems: A review

The aqueous two-phase system (ATPS) is an all-aqueous system fabricated from two immiscible aqueous phases. It is spontaneously assembled through physical liquid-liquid phase separation (LLPS) and can create suitable templates like the multicompartment of the intracellular environment. Delicate structures containing multiple compartments make it possible to endow materials with advanced functions. Due to the properties of ATPSs, ATPS-based drug delivery systems exhibit excellent biocompatibility, extraordinary loading efficiency, and intelligently controlled content release, which are particularly advantageous for delivering drugs in vivo . Therefore, we will systematically review and evaluate ATPSs as an ideal drug delivery system. Based on the basic mechanisms and influencing factors in forming ATPSs, the transformation of ATPSs into valuable biomaterials is described. Afterward, we concentrate on the most recent cutting-edge research on ATPS-based delivery systems. Finally, the potential for further collaborations between ATPS-based drug-carrying biomaterials and disease diagnosis and treatment is also explored.

Advanced Technologies of Drug Delivery to the Posterior Eye Segment Targeting Angiogenesis and Ocular Cancer

Retinoblastoma (RB), a childhood retinal cancer is caused due to RB1 gene mutation which affects the child below 5 years of age. Angiogenesis has been proven its role in RB metastasis due to the presence of vascular endothelial growth factor (VEGF) in RB cells. Therefore, exploring angiogenic pathway by inhibiting VEGF in treating RB would pave the way for future treatment. In preclinical studies, anti-VEGF molecule have shown their efficacy in treating RB. However, treatment requires recurrent intra-vitreal injections causing various side effects along with patient nonadherence. As a result, delivery of anti-VEGF agent to retina requires an ocular delivery system that can transport it in a non-invasive manner to achieve patient compliance. Moreover, development of these type of systems are challenging due to the complicated physiological barriers of eye. Adopting a non-invasive or minimally invasive approach for delivery of anti-VEGF agents would not only address the bioavailability issues but also improve patient adherence to therapy overcoming the side effects associated with invasive approach. The present review focuses on the eye cancer, angiogenesis and various novel ocular drug delivery systems that can facilitate inhibition of VEGF in the posterior eye segment by overcoming the eye barriers.

Application of iontophoresis in ophthalmic practice: an innovative strategy to deliver drugs into the eye

Delivery of drugs to special locations of ocular lesions, while minimizing systemic and local toxic effects, is recognized as a critical challenge in the ophthalmic practice. The special anatomy and physiology barriers within the eyeball entail effective drug delivery systems. Emerging attempts in drug delivery has led to developments in ocular iontophoresis, which acts as a noninvasive technology to enhance drug penetration using a small electric current. This technique offers greater flexibility to deliver desired drug dose in a controlled and tolerable manner. In previous studies, this technique has been testified to deliver antibiotics, corticoid, proteins and other gene drugs into the eye with the potency of treating or alleviating diverse ophthalmological diseases including uveitis, cataract, retinoblastoma, herpes simplex and cytomegalovirus retinitis (CMVR), etc. In this review, we will introduce the recent developments in iontophoresis device. We also summarize the latest progress in coulomb controlled iontophoresis (CCI), hydrogel ionic circuit (HIC) and EyeGate II delivery system (EGDS), as well as overview the potential toxicity of iontophoresis. We will discuss these factors that affect the efficacy of iontophoresis experiments, and focus on the latest progress in its clinical application in the treatment of eye diseases.

In Vivo Electroporation Improves Retinal Delivery of Intravitreally Injected Exosomes

Purpose: Mesenchymal stem cell (MSC)-derived exosomes are promising therapeutic agents and natural nanoscale delivery platforms for treating degenerative retinal diseases. This study investigated the effect of electroporation on the retinal delivery of intravitreally administered MSC-derived exosomes in a murine model. Methods: Exosomes isolated from adipose tissue-derived MSCs were stained with ExoGlow exosome-specific dye and administered to the right eyes of 40 Sprague-Dawley rats. Electroporation was performed in 20 rats immediately after intravitreal injection (electroporation group); 5 square pulses of 40 V/cm for 50 ms each with 950-ms intervals were administered. The remaining 20 rats were assigned to the no-electroporation group. The eyeballs were harvested 24 h later for evaluation. The total number of fluorescent particles per hyperfield was counted from the retinal flat mounts to quantify the retinal delivery of exosomes. Tissue damage after electroporation was evaluated using retinal histological sections and a terminal deoxynucleotidyl transferase-mediated deoxyuridine nick end labeling (TUNEL) assay. Results: A significantly higher number of fluorescent particles per hyperfield were observed in the retinal flat mounts of the electroporation group compared with that in the no-electroporation group (599.0 ± 307.5 vs. 376.9 ± 175.4; P = 0.013). Retinal histological sections and TUNEL assays showed no signs of tissue damage after electroporation. Conclusions: In vivo electroporation can improve the retinal delivery of intravitreally injected exosomes.

Application of Hydrogels in the Device of Ophthalmic Iontophoresis: Theory, Developments and Perspectives

The human eye is a consolidated organ with delicate structures and unique immune privileges. Ocular diseases are intractable due to the intrinsic biological barriers within the eyeball. Hydrogels are excellent drug-carrying substances with soft material and excellent properties. They have been extensively used to deliver drugs into ocular tissue via iontophoresis devices. Ophthalmic iontophoresis is an electrochemical technique using tiny electrical currents to deliver drugs into the eye non-invasively. The early infantile iontophoresis technique often required long applying time to achieve therapeutic dose in the posterior ocular segment. The potential limitations in the initial drug concentration and the maximum safe currents would also impede the efficiency and safety of iontophoresis. Moreover, the poor patient compliance always leads to mechanical damage to the cornea and sclera during application. Advantageously, the flexible drug-carrying hydrogel can be in direct contact with the eye during iontophoresis, thereby reducing mechanical damage to the ocular surface. Moreover, the water absorption and adjustable permeability of hydrogels can reduce the electrochemical (EC) reactions and enhance the efficiency of iontophoresis. In this review, we focus on recent developments of hydrogels iontophoresis in ophthalmologic practice. Refinements of the knowledge would provide an outlook for future application of hydrogels in treating ocular disease.

Dendrimers in Corneal Drug Delivery: Recent Developments and Translational Opportunities

Dendrimers are biocompatible organic nanomaterials with unique physicochemical properties, making them the focus of recent research in drug delivery. The cornea of the human eye presents a challenge for drug transit due to its inherently impenetrable nature, requiring nanocarrier-mediated targeted drug delivery. This review intends to examine recent advancements in the use of dendrimers for corneal drug delivery, including their properties and their potential for treating various ocular diseases. The review will also highlight the benefit of the novel technologies that have been developed and applied in the field, such as corneal targeting, drug release kinetics, treatments for dry eye disease, antibacterial drug delivery, corneal inflammation, and corneal tissue engineering. The review seeks to provide a comprehensive overview of the current state of research in this field, along with the translational developments in the field of dendrimer-based therapeutics and imaging agents and inspire the potential for future developments and translational opportunities in dendrimers based corneal drug delivery.

Trans-corneal drug delivery strategies in the treatment of ocular diseases

The cornea is a remarkable tissue that possesses specialized structures designed to safeguard the eye against foreign objects. However, its unique properties also make it challenging to deliver drugs in a non-invasive manner. This review highlights recent advancements in achieving highly efficient drug transport across the cornea, focusing on nanomaterials. We have classified these strategies into three main categories based on their mechanisms and have analyzed their success and limitations in a systematic manner. The purpose of this review is to examine potential general principles that could improve drug penetration through the cornea and other natural barriers in the eye. We hope it will inspire the development of more effective drug delivery systems that can better treat ocular diseases.

Ocular therapies with biomacromolecules: From local injection to eyedrop and emerging noninvasive delivery strategies

The last two decades have witnessed a continuously increasing number of biomacromolecules approved for the treatment of ocular diseases. The eye possesses multiple protective mechanisms to resist the invasion of exogenous substances, but meanwhile these physiological defense systems also act as strong barriers, impeding absorption of most biomacromolecules into the eye. As a result, local injections play predominant roles for posterior ocular delivery of biomacromolecules in clinical practice. To achieve safe and convenient application of biomacromolecules, alternative strategies to realize noninvasive intraocular delivery are necessary. Various nanocarriers, novel penetration enhancers and physical strategies have been explored to facilitate delivery of biomacromolecules to both anterior and posterior ocular segments but still suffered difficulties in clinical translation. This review compares the anatomical and physiological characteristics of the eyes from those frequently adopted experimental species and profiles the well-established animal models of ocular diseases. We also summarize the ophthalmic biomacromolecules launched on the market and put emphasis on emerging noninvasive intraocular delivery strategies of peptides, proteins and genes.

Smart Contact Lens Systems for Ocular Drug Delivery and Therapy

Ocular drug delivery and therapy systems have been extensively investigated with various methods including direct injections, eye drops and contact lenses. Nowadays, smart contact lens systems are attracting a lot of attention for ocular drug delivery and therapy due to their minimally invasive or non-invasive characteristics, highly enhanced drug permeation, high bioavailability, and on-demand drug delivery. Furthermore, smart contact lens systems can be used for direct light delivery into the eyes for biophotonic therapy replacing the use of drugs. Here, we review smart contact lens systems which can be classified into two groups of drug-eluting contact lens and ocular device contact lens. More specifically, this review covers smart contact lens systems with nanocomposite-laden systems, polymeric film-incorporated systems, micro and nanostructure systems, iontophoretic systems, electrochemical systems, and phototherapy systems for ocular drug delivery and therapy. After that, we discuss the future opportunities, challenges and perspectives of smart contact lens systems for ocular drug delivery and therapy.

Challenges in Age-Related Macular Degeneration: From Risk Factors to Novel Diagnostics and Prevention Strategies

Age-related macular degeneration (AMD) is a chronic multifactorial eye disease representing the primary cause of vision loss in people aged 60 years and older. The etiopathogenesis of the disease remains uncertain, with several risk factors contributing to its onset and progression, such as genotype, aging, hypertension, smoking, overweight, and low dietary intake of carotenoids. Since the aging populations of the industrialized world are increasing rapidly, the impact of AMD in the socio-economical life-developed countries is expected to increase dramatically in the next years. In this context, the benefits of prevention and early disease detection for prompt and effective treatment can be enormous to reduce the social and economic burden of AMD. Nutritional and lifestyle changes, including dietary intake of xanthophyll pigments, such as lutein and zeaxanthin, no smoking, and regular exercise, are known to protect from risk of AMD progression from early to advanced disease stages. In this review, we present the clinical outcomes of a pilot study on trans-scleral iontophoresis delivery of lutein in patients with AMD. Topical delivery of lutein directly to the macula may provide a more efficient method for enriching the macular pigment and for achieving greater patient compliance to therapy than oral administration and thus enhancing prevention strategies. Modern diagnostic methodologies shall address the major problem of accurately detecting the risk of transition from intermediate AMD to advanced AMD stages. Adaptive optics retinal imaging and resonance Raman spectroscopy are two highly promising technologies for the objective assessment of patients with AMD. In this review, we present some of their clinical applications for collecting quantitative measurements of retinal cellular changes and macular content of xanthophyll pigments, respectively. In conclusion, there is great expectation that technological advancements in AMD management will deliver improved screening, therapeutic prevention, and diagnostic systems in the coming decade through a pro-active strategy of “treatment for prevention” that will aim to reduce the global burden of vision loss caused by AMD in the elderly.

Iontophoretic ocular delivery of latanoprost-loaded nanoparticles via skin-attached electrodes

Prolonged drug efficacy to reduce the number of administrations is a key factor in the successful treatment of glaucoma through topical drug delivery to the eye. Therefore, we propose a new strategy for iontophoretic ocular delivery of drug-loaded nanoparticles. Considering safety and convenience, our strategy is involved with topical administration of the drug-loaded nanoparticles followed by their permeation into the eye tissues via noninvasive iontophoresis, using the skin-attached electrodes. Thus, those nanoparticles stayed longer in the eye, and during this period, the drug was released in a sustained manner, thereby prolonging drug exposure even with one-time treatment. The nanoparticles were made of poly(lactic-co-glycolic acid) (PLGA), which were loaded with a glaucoma drug, latanoprost. We varied the size of the nanoparticles at 100, 200, 300, and 500 nm and sought to find the optimum size under the fixed conditions for iontophoresis proposed in this work (4 mA; 30 min). Even with iontophoresis through the skin-attached electrodes, the nanoparticles were indeed deposited in the eye tissues, where with an increase in particle size, drug release was more sustained, but fewer particles could permeate into the eye tissues. Because of these two competing factors, iontophoretic delivery of the 300-nm particles exhibited the most prolonged drug efficacy in vivo for more than 7 days, and showed an approximately 23-fold increase in drug efficacy compared with that of Xalatan®, a commercially available eye drop of latanoprost developed for once-a-day administration every day. STATEMENT OF SIGNIFICANCE: To treat glaucoma, conventional eye drops are often prescribed; however, they often require multiple daily administrations due to rapid preocular clearance. To resolve this, we suggest a noninvasive iontophoretic ocular delivery of latanoprost-loaded PLGA nanoparticles using the skin-attached electrodes. Even with iontophoresis via the skin-attached electrodes, the nanoparticles can indeed be deposited into the eye tissues. However, with an increase in particle size, fewer particles can permeate into the eye tissues, although drug release is more sustained. Therefore, the particles with a size of 300 nm show the optimal in vivo delivery profile in this work, where the drug efficacy can be extended for more than 7 days with a single administration.

A Hydrogel Ionic Circuit Based High-Intensity Iontophoresis Device for Intraocular Macromolecule and Nanoparticle Delivery

Iontophoresis is an electrical-current-based, noninvasive drug-delivery technology, which is particularly suitable for intraocular drug delivery. Current ocular iontophoresis devices use low current intensities that significantly limit macromolecule and nanoparticle (NP) delivery efficiency. Increasing current intensity leads to ocular tissue damage. Here, an iontophoresis device based on a hydrogel ionic circuit (HIC), for high-efficiency intraocular macromolecule and NP delivery, is described. The HIC-based device is capable of minimizing Joule heating, effectively buffering electrochemical (EC) reaction-generated pH changes, and absorbing electrode overpotential-induced heating. As a result, the device allows safe application of high current intensities (up to 87 mA cm-2 , more than 10 times higher than current ocular iontophoresis devices) to the eye with minimal ocular cell death and tissue damage. The high-intensity iontophoresis significantly enhances macromolecule and NP delivery to both the anterior and posterior segments by up to 300 times compared to the conventional iontophoresis. Therapeutically effective concentrations of bevacizumab and dexamethasone are delivered to target tissue compartments within 10-20 min of iontophoresis application. This study highlights the significant safety enhancement enabled by an HIC-based device design and the potential of the device to deliver therapeutic doses of macromolecule and NP ophthalmic drugs within a clinically relevant time frame.

In-vivo estimation of tissue electrical conductivities of a rabbit eye for precise simulation of electric field distributions during ocular iontophoresis

Precise estimation of electrical conductivity of the eyes is important for the accurate analysis of electric field distributions in the eyes during ocular iontophoresis. In this study, we estimated the tissue electrical conductivities of a rabbit eye, which has been widely employed for neuro-ophthalmological experiments, through an in vivo experiment for the first time. Electrical potentials were measured at multiple locations on the skin, while weak currents were transmitted into the skin via two surface electrodes attached to the skin around the eye. A finite element model was constructed to calculate the electric potentials at the measurement locations. The conductivity values of different tissues were then estimated using an optimization procedure to minimize the difference between the measured and calculated electric potentials. The accuracy of the estimated tissue conductivity values of the rabbit eye was validated by comparing the measured and calculated electric potential values for different electrode montages. Further multi-physical analyses of iontophoretic drug delivery to the rabbit eye showed a significant influence of the conductivity profile on the resultant particle distribution. Overall, our results provide an important reference for the tissue electrical conductivity values of the rabbit eye, which could be further utilized for designing new medical devices for delivering electric fields to the eyes, such as transorbital and transscleral electrical stimulations.

[Ocular iontophoresis]

Iontophoresis in medicine is a combined pharmacological and physical method of treatment that unites the therapeutic effect of an electric current with the pharmacological effect of medicinal substances administered at the same time via an electric current. The article describes the physical basis of the therapeutic effect of direct electric current on biological tissues, and highlights the physical and chemical mechanisms of target administration of pharmaceutical substances into the human body through intact skin or mucous membrane by means of direct electric current. In addition, it presents the results of international as well as Russian domestic scientific studies on the clinical effectiveness of iontophoresis in ophthalmology.

Enhanced topical corticosteroids delivery to the eye: A trade-off in strategy choice

Topical corticosteroids are the primary treatment of ocular inflammation caused by surgery, injury, or other conditions. Drug pre-corneal residence time, drug water solubility, and drug corneal permeability coefficient are the major factors that determine the ocular drug bioavailability after topical administration. Although growing research successfully enhanced local delivery of corticosteroids utilizing various strategies, rational and dynamic approaches to strategy selection are still lacking. Within this review, an overview of the various strategies as well as their performance in retention, solubility, and permeability coefficient of corticosteroids are provided. On this basis, the tradeoff of strategy selection is discussed, which may shed light on the rational choice and application of ophthalmic delivery enhancement strategies.

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 Review on Newer Ocular Drug Delivery Systems with an Emphasis on Glaucoma

Glaucoma is an irreversible condition resulting from the increase in intraocular pressure (IOP); which leads to permanent loss of vision with the destruction of retinal ganglion cells (RGCs). The IOP elevations are controlled in normal by the physiological flow of aqueous humour. A population with age above 40 is more susceptible to glaucoma. Other factors like gender, genetics, race etc. plays major roles in the development of the disease. Current treatment methods available for the disease includes drugs come under the classes of beta receptor blockers, carbonic anhydrase inhibitors, cholinergic agonists, prostaglandins etc. N-methyl-D-aspartate (NMDA) antagonists, inducible nitric oxide synthase (iNOS) inhibition, cytoskeletal agents, Rho-kinase inhibitors etc are few novel targets sites which are in research focus for the treatment of the disease. Developments in nanomedicine are also being evaluated for their potential in treating the growing glaucomatous population. Nanosystems are suggested to avoid the difficulties in tackling the various ocular barriers to a limit, help to decrease the instillation frequency of topical medication and can provide drug delivery in a sustained or controlled manner. This review focuses on the current and emerging treatment methods for glaucoma along with some of the nanoformulations for ocular drug delivery.

Smart nano-micro platforms for ophthalmological applications: The state-of-the-art and future perspectives

Smart nano-micro platforms have been extensively applied for diverse biomedical applications, mostly focusing on cancer therapy. In comparison with conventional nanotechnology, the smart nano-micro matrix can exhibit specific response to exogenous or endogenous triggers, and thus can achieve multiple functions e.g. site-specific drug delivery, bio-imaging and detection of bio-molecules. These intriguing techniques have expanded into ophthalmology in recent years, yet few works have been summarized in this field. In this work, we provide the state-of-the-art of diverse nano-micro platforms based on both the conventional materials (e.g. natural or synthetic polymers, lipid nanomaterials, metal and metal oxide nanoparticles) and emerging nanomaterials (e.g. up-conversion nanoparticles, quantum dots and carbon materials) in ophthalmology, with some smart nano/micro platformers highlighted. The common ocular diseases studied in the field of nano-micro systems are firstly introduced, and their therapeutic method and the related drawback in clinic treatment are presented. The recent progress of different materials for diverse ocular applications is then demonstrated, with the representative nano- and micro-systems highlighted in detail. At last, an in-depth discussion on the clinical translation challenges faced in this field and the future direction are provided. This review would allow the researchers to design more smart nanomedicines in a more rational manner for specific ophthalmology applications.

Novel Drug Delivery Systems Fighting Glaucoma: Formulation Obstacles and Solutions

Glaucoma is considered to be one of the biggest health problems in the world. It is the main cause of preventable blindness due to its asymptomatic nature in the early stages on the one hand and patients' non-adherence on the other. There are several approaches in glaucoma treatment, whereby this has to be individually designed for each patient. The first-line treatment is medication therapy. However, taking into account numerous disadvantages of conventional ophthalmic dosage forms, intensive work has been carried out on the development of novel drug delivery systems for glaucoma. This review aims to provide an overview of formulation solutions and strategies in the development of in situ gel systems, nanosystems, ocular inserts, contact lenses, collagen corneal shields, ocular implants, microneedles, and iontophoretic devices. The results of studies confirming the effectiveness of the aforementioned drug delivery systems were also briefly presented.

Modeling iontophoretic drug delivery in a microfluidic device

Iontophoresis employs low-intensity electrical voltage and continuous constant current to direct a charged drug into a tissue. Iontophoretic drug delivery has recently been used as a novel method for cancer treatment in vivo. There is an urgent need to precisely model the low-intensity electric fields in cell culture systems to optimize iontophoretic drug delivery to tumors. Here, we present an iontophoresis-on-chip (IOC) platform to precisely quantify carboplatin drug delivery and its corresponding anti-cancer efficacy under various voltages and currents. In this study, we use an in vitro heparin-based hydrogel microfluidic device to model the movement of a charged drug across an extracellular matrix (ECM) and in MDA-MB-231 triple-negative breast cancer (TNBC) cells. Transport of the drug through the hydrogel was modeled based on diffusion and electrophoresis of charged drug molecules in the direction of an oppositely charged electrode. The drug concentration in the tumor extracellular matrix was computed using finite element modeling of transient drug transport in the heparin-based hydrogel. The model predictions were then validated using the IOC platform by comparing the predicted concentration of a fluorescent cationic dye (Alexa Fluor 594®) to the actual concentration in the microfluidic device. Alexa Fluor 594® was used because it has a molecular weight close to paclitaxel, the gold standard drug for treating TNBC, and carboplatin. Our results demonstrated that a 50 mV DC electric field and a 3 mA electrical current significantly increased drug delivery and tumor cell death by 48.12% ± 14.33 and 39.13% ± 12.86, respectively (n = 3, p-value <0.05). The IOC platform and mathematical drug delivery model of iontophoresis are promising tools for precise delivery of chemotherapeutic drugs into solid tumors. Further improvements to the IOC platform can be made by adding a layer of epidermal cells to model the skin.

Corticosteroids in ophthalmology: drug delivery innovations, pharmacology, clinical applications, and future perspectives

Corticosteroids remain the mainstay of the treatment for various ocular conditions affecting the ocular surface, anterior and posterior segments of the eye due to their anti-inflammatory, anti-oedematous, and anti-neovascularization properties. Prednisolone, prednisolone acetate, dexamethasone, triamcinolone acetonide, fluocinolone acetonide, and loteprednol etabonate are amongst the most widely used ophthalmic corticosteroids. Corticosteroids differ in their activity and potency in the eye due to their inherent pharmacological and pharmaceutical differences. Different routes and regimens are available for ocular administration of corticosteroids. Conventional topical application to the eye is the route of choice when targeting diseases affecting the ocular surface and anterior segment, while periocular, intravitreal, and suprachoroidal injections can be potentially effective for posterior segment diseases. Corticosteroid-induced intraocular pressure elevation and cataract formation remain the most significant local risks following topical as well as systemic corticosteroid administration. Invasive drug administration via intracameral, subconjunctival, and intravitreal injection can enhance ocular bioavailability and minimize dose and dosing frequency of administration, yet may exacerbate ocular side effects of corticosteroids. This review provides a critical appraisal of the ophthalmic uses of corticosteroid, routes of administration, drug delivery fundamentals and novel ocular implantable steroid delivery systems, factors influencing side effects, and future perspectives for ocular corticosteroid therapy.

Physical triggering strategies for drug delivery

Physically triggered systems hold promise for improving drug delivery by enhancing the controllability of drug accumulation and release, lowering non-specific toxicity, and facilitating clinical translation. Several external physical stimuli including ultrasound, light, electric fields and magnetic fields have been used to control drug delivery and they share some common features such as spatial targeting, spatiotemporal control, and minimal invasiveness. At the same time, they possess several distinctive features in terms of interactions with biological entities and/or the extent of stimulus response. Here, we review the key advances of such systems with a focus on discussing their physical mechanisms, the design rationales, and translational challenges.

Ocular Disease Therapeutics: Design and Delivery of Drugs for Diseases of the Eye

The ocular drug discovery field has evidenced significant advancement in the past decade. The FDA approvals of Rhopressa, Vyzulta, and Roclatan for glaucoma, Brolucizumab for wet age-related macular degeneration (wet AMD), Luxturna for retinitis pigmentosa, Dextenza (0.4 mg dexamethasone intracanalicular insert) for ocular inflammation, ReSure sealant to seal corneal incisions, and Lifitegrast for dry eye represent some of the major developments in the field of ocular therapeutics. A literature survey also indicates that gene therapy, stem cell therapy, and target discovery through genomic research represent significant promise as potential strategies to achieve tissue repair or regeneration and to attain therapeutic benefits in ocular diseases. Overall, the emergence of new technologies coupled with first-in-class entries in ophthalmology are highly anticipated to restructure and boost the future trends in the field of ophthalmic drug discovery. This perspective focuses on various aspects of ocular drug discovery and the recent advances therein. Recent medicinal chemistry campaigns along with a brief overview of the structure-activity relationships of the diverse chemical classes and developments in ocular drug delivery (ODD) are presented.

Hydrogel Biomaterials for Application in Ocular Drug Delivery

There are many challenges involved in ocular drug delivery. These are a result of the many tissue barriers and defense mechanisms that are present with the eye; such as the cornea, conjunctiva, the blinking reflex, and nasolacrimal drainage system. This leads to many of the conventional ophthalmic preparations, such as eye drops, having low bioavailability profiles, rapid removal from the administration site, and thus ineffective delivery of drugs. Hydrogels have been investigated as a delivery system which is able to overcome some of these challenges. These have been formulated as standalone systems or with the incorporation of other technologies such as nanoparticles. Hydrogels are able to be formulated in such a way that they are able to change from a liquid to gel as a response to a stimulus; known as "smart" or stimuli-responsive biotechnology platforms. Various different stimuli-responsive hydrogel systems are discussed in this article. Hydrogel drug delivery systems are able to be formulated from both synthetic and natural polymers, known as biopolymers. This review focuses on the formulations which incorporate biopolymers. These polymers have a number of benefits such as the fact that they are biodegradable, biocompatible, and non-cytotoxic. The biocompatibility of the polymers is essential for ocular drug delivery systems because the eye is an extremely sensitive organ which is known as an immune privileged site.

Transscleral Iontophoresis for Noninvasive Ocular Drug Delivery of Macromolecules

Purpose: The objectives were to investigate the effect of transscleral iontophoresis of macromolecules in vitro and in vivo, to study the importance of electroosmosis on macromolecules of low charge to mass ratio, and to evaluate transscleral iontophoresis efficacy in a choroidal neovascularization (CNV) animal model. Methods: Through in vitro transport experiments, the permeability coefficients of macromolecules [eg, immunoglobulin G (IgG), dextran 70 kDa] were determined under different conditions. The effect of ionic strength formulations and iontophoretic conditions was studied on the distribution of IgG and bevacizumab into the eye in vivo. Magnetic resonance imaging (MRI) was utilized to evaluate in vivo real time distribution of gadolinium-labeled albumin (Galbumin) following iontophoresis. The efficacy between no treatment, intravitreal injection (IVT), and iontophoresis of bevacizumab on a CNV model of subretinal injection of adeno-associated virus encoding human VEGF-165 was investigated. Results: The permeability data suggested a significant effect of ionic strength on the iontophoretic transport of macromolecules. Transscleral iontophoresis of IgG at 4 mA with a low ionic strength formulation was about 600 times greater than passive diffusion and 14-fold over a conventional formulation in vitro. Approximately 0.6 mg of bevacizumab can be delivered into the rabbit eye in vivo with a 20-min treatment of iontophoresis. MRI showed that Galbumin was in the posterior tissues after iontophoresis. In the CNV model, the iontophoresis and IVT methods of bevacizumab delayed retinal neovascularization by 4 and 8 weeks, respectively. Conclusions: Transscleral iontophoresis is capable of delivering macromolecule drugs through the conjunctiva and sclera, eventually exposing the retina/choroid to the drugs.

The Use of Electrotherapeutics in Ophthalmology

PURPOSE

To present a perspective on the use of electrotherapeutics in the history of ophthalmology along with the development of novel contemporary ophthalmic instrumentation.

DESIGN

Perspective study.

METHODS

We reviewed historical journals, articles, and books discussing the use of electricity and electrotherapeutics in ophthalmology.

RESULTS

Electrotherapeutic applications have been researched and used to treat ocular diseases as far back as the 18th century. By the 20th century, research in electrotherapeutics in ophthalmology had caught the eye of Edward Jackson, the first president of the American Academy of Ophthalmology and Otolaryngology and first editor of the present (third) series American Journal of Ophthalmology. Edward Jackson published an extensive review on this topic and reported a variety of modalities used to treat ocular diseases.

CONCLUSIONS

While many early therapeutic uses of electricity did not produce effective and replicable results, studies on electrical stimulation of the eye provided the foundation for the development of clinically significant vision enhancing and restoring instrumentation.

Iontophoretic Dexamethasone Phosphate Compared to Topical Prednisolone Acetate 1% for Noninfectious Anterior Segment Uveitis

PURPOSE

To evaluate the safety and efficacy of dexamethasone phosphate ophthalmic solution (EGP-437) delivered by a transscleral iontophoresis delivery system (EyeGate II) compared to that of topical prednisolone acetate 1% (PA 1%) in subjects with noninfectious anterior uveitis.

DESIGN

Prospective, randomized, double-masked, parallel group, noninferiority clinical trial.

METHODS

A total of 193 subjects with active noninfectious anterior uveitis (anterior chamber [AC] cell count ≥11 cells) were randomized to EGP-437 delivered by iontophoresis (days 0 and 7) or self-administered PA 1% daily (tapered schedule, days 0-28). Masking was maintained with placebo iontophoresis or eye drops. The primary efficacy endpoint was the proportion of subjects with an AC cell count of zero on day 14. Noninferiority of EGP-437 was defined if the lower limit of the confidence interval (CI) for the difference (EGP-437 minus PA 1%) was less than -10%.

RESULTS

At day 14, 32 of 96 EGP-437 subjects (33.3%) and 32 of 97 PA 1% subjects (33.0%) had an AC cell count of zero (difference, 0.34; 95% CI, -12.94 to 13.63; P = 0.064). Efficacy trended better with EGP-437 among patients with more severe baseline uveitis (AC cell count >25). Safety and tolerability were good with both treatments. EGP-437 subjects experienced fewer IOP elevations ≥6 mm Hg versus PA 1% subjects (13 vs 24 incidents, respectively, through day 28).

CONCLUSIONS

Despite clinically similar response rates, statistical noninferiority of EGP-437 versus a tapered regimen of PA 1% was not achieved. Numerical trends suggesting fewer IOP elevations with EGP-437, similar efficacy overall, and possibly better efficacy in more severe disease warrant further study.

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.

Extended release of dexamethasone from oleogel based rods

HYPOTHESIS

Topical and systemic methods are not able to deliver ophthalmic drugs for treatment of retinal diseases. Consequently, invasive monthly intravitreal injections through the eyeball are required to deliver retinal drugs. A reduction in the frequency of the injection through extended release of the drugs could have significant clinical benefits.

EXPERIMENTS

Oleogels containing ethyl cellulose as the gelator at 10% (wt%) in soybean oil were loaded with dexamethasone above the solubility limit and expunged from a syringe to create cylindrical rods for extended drug delivery. The devices were imaged to explore particle distribution and drug release was measured under sink conditions in buffer. A model was developed and fitted to data to determine effective drug diffusivity.

FINDINGS

Dexamethasone is released slowly due to the presence of the drug particles that serve as drug depots. The release increases from 600 to 3000 h as the drug loading is increased from 3% to 28%. The release profiles can be modeled by considering drug dissolution and diffusion, as well as the tortuosity of the matrix due to the presence of the voids formed after the drug particles have dissolved. The proposed approach is promising as the release profiles of the drug are comparable to commercial devices.

Effective In Vivo Topical Delivery of siRNA and Gene Silencing in Intact Corneal Epithelium Using a Modified Cell-Penetrating Peptide

Autosomal dominantly inherited genetic disorders such as corneal dystrophies are amenable to allele-specific gene silencing with small interfering RNA (siRNA). siRNA delivered to the cornea by injection, although effective, is not suitable for a frequent long-term treatment regimen, whereas topical delivery of siRNA to the cornea is hampered by the eye surface's protective mechanisms. Herein we describe an attractive and innovative alternative for topical application using cell-penetrating peptide derivatives capable of complexing siRNA non-covalently and delivering them into the cornea. Through a rational design approach, we modified derivatives of a cell-penetrating peptide, peptide for ocular delivery (POD), already proved to diffuse into the corneal layers. These POD derivatives were able to form siRNA-peptide complexes (polyplexes) of size and ζ-potential similar to those reported able to undergo cellular internalization. Successful cytoplasmic release and gene silencing in vitro was obtained when an endosomal disruptor, chloroquine, was added. A palmitoylated-POD, displaying the best delivery properties, was covalently functionalized with trifluoromethylquinoline, an analog of chloroquine. This modified POD, named trifluoromethylquinoline-palmitoyl-POD (QN-Palm-POD), when complexed with siRNA and topically applied to the eye in vivo, resulted in up to 30% knockdown of luciferase reporter gene expression in the corneal epithelium. The methods developed within represent a valid standardized approach that is ideal for screening of a range of delivery formulations.

Targeting drug delivery within the suprachoroidal space

The suprachoroidal space (SCS), a potential anatomical space between the sclera and choroid, is a novel route for drug delivery targeting the chorioretinal layers of the eye. The safety and efficacy of SCS drug delivery have been shown in multiple clinical trials. Recent studies have developed methods for more precise targeting within the SCS at sites of action at the posterior pole (e.g., macula), near the limbus (e.g., ciliary body), and throughout the SCS using iontophoresis, swollen hydrogels, high-density particle emulsions, highly viscous and non-Newtonian fluids, and microstents. Here, we review novel technologies targeting the posterior, anterior, or entire SCS.

ISOPT Clinical Hot Topic Panel Discussion on Ocular Drug Delivery

Ocular drug delivery offers unique challenges and opportunities in the era of novel therapeutic agents ranging from small molecules to gene therapies. Noninvasive delivery of drugs into the back of the eye or any part of the eye is extremely limited by short precorneal residence time and formidable biological barriers. The eye is a sensitive, sensory organ that requires a high level of material and procedural safety, while achieving therapeutic efficacy. Some recent advances and unmet needs for ocular drug delivery and disposition are discussed in this article. Specifically, nanomedicines, physical and chemical means to enhance delivery, stimuli-responsive delivery systems, the role of vitreal binding on ocular pharmacokinetics, and the influence of aging eye on drug delivery, and the associated unmet needs are highlighted. Additionally, the unmet needs in the medication management for the elderly patients with eye diseases are discussed.

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.

Trans-ocular Electric Current In Vivo Enhances AAV-Mediated Retinal Gene Transduction after Intravitreal Vector Administration

Adeno-associated virus (AAV) vector-mediated gene delivery is a promising approach for therapy, but implementation in the eye currently is hampered by the need for delivering the vector underneath the retina, using surgical application into the subretinal space. This limits the extent of the retina that is treated and may cause surgical injury. Vector delivery into the vitreous cavity would be preferable because it is surgically less invasive and would reach more of the retina. Unfortunately, most conventional, non-modified AAV vector serotypes penetrate the retina poorly from the vitreous; this limits efficient transduction and expression by target cells (retinal pigment epithelium and photoreceptors). We developed a method of applying a small and safe electric current across the intact eye in vivo for a brief period following intravitreal vector administration. This significantly improved AAV-mediated transduction of retinal cells in wild-type mice following intravitreal delivery, with gene expression in retinal pigment epithelium and photoreceptor cells. The low-level current had no adverse effects on retinal structure and function. This method should be generally applicable for other AAV serotypes and may have broad application in both basic research and clinical studies.

Controlled non-invasive iontophoretic delivery of triamcinolone acetonide amino acid ester prodrugs into the posterior segment of the eye

This study investigated short duration transscleral iontophoretic delivery of four triamcinolone acetonide (TA) amino acid ester prodrugs (TA-AA) (alanine, Ala; arginine, Arg; isoleucine, Ile and lysine, Lys) using whole porcine eyes globes in vitro. Post-iontophoretic biodistribution of TA was quantified by UHPLC-MS/MS in the different ocular compartments (cornea, aqueous humor, sclera, ciliary body, choroid and retinal pigmented epithelium (RPE), neural retina and vitreous humor). Transscleral iontophoresis (3 mA/cm² for 10 min) increased total drug delivery of the TA-AA prodrugs by 14-30-fold as compared to passive diffusion. The TA-AA prodrugs had distinct biodistribution profiles - the penetration depth achieved was dependent on their physicochemical properties (e.g. lipophilicity for TA-Ile) and susceptibility to hydrolysis (e.g. TA-Arg). Intraocular drug distribution was also influenced by prodrug binding to melanin (TA-Lys). Interestingly, under conditions of equivalent charge (6 mA/cm² for 5 min vs. 1.5 mA/cm² for 20 min, i.e. 1.44 C respectively) the longer duration (20 min) at lower current density resulted in ∼6 times more TA delivery into the vitreous humor. Overall, the study provided further evidence of the potential of transscleral iontophoresis for the non-invasive treatment of posterior segment inflammatory diseases.

A comprehensive review on contact lens for ophthalmic drug delivery

With the prevalence of electronic devices and an aging population, the number of people affected with eye disease is increasing year by year. In spite of a large number of eye drops on the market, most of them do not perform sufficiently, due to rapid clearance mechanisms and ocular barriers. To enhance drug delivery to the eye, a number of novel formulations for ocular diseases have been investigated over recent decades, aiming to increase drug retention and permeation while also allowing for sustained drug release over prolonged periods. The contact lens, initially used to correct visual acuity and beautify female eyes, is one such novel formulation with outstanding potential. Recently, contact lenses have been extensively used for ocular drug delivery to enhance ocular bioavailability and reduce side effects, and are particularly suitable for the treatment of chronic diseases, and thus are of interest to ophthalmic scientists. This review summarizes contact lens classification, methods of preparation, strategies for integrating drugs into lenses, in vitro and in vivo studies, and clinical applications. This review also discusses the current state of ocular drug therapy and provides an outlook for future therapeutic opportunities in the field of ocular drug delivery.

Efficacy of iontophoresis-assisted epithelium-on corneal cross-linking for keratoconus

Corneal cross-linking (CXL) is a noninvasive therapeutic procedure for keratoconus that is aimed at improving corneal biomechanical properties by induction of covalent cross-links between stromal proteins. It is accomplished by ultraviolet A (UVA) radiation of the cornea, which is first saturated with photosensitizing riboflavin. It has been shown that standard epithelium-off CXL (S-CXL) is efficacious, and it has been recommended as the standard of care procedure for keratoconus. However, epithelial removal leads to pain, transient vision loss, and a higher risk of corneal infection. To avoid these disadvantages, transepithelial CXL was developed. Recently, iontophoresis has been adopted to increase riboflavin penetration through the epithelium. Several clinical observations have demonstrated the safety and efficacy of iontophoresis-assisted epithelium-on CXL (I-CXL) for keratoconus. This review aimed to provide a comprehensive summary of the published studies regarding I-CXL and a comparison between I-CXL and S-CXL. All articles used in this review were mainly retrieved from the PubMed database. Original articles and reviews were selected if they were related to the I-CXL technique or related to the comparison between I-CXL and S-CXL.

Drug delivery devices for retinal diseases

Retinal degenerative diseases are a leading cause of irreversible blindness and visual impairment, affecting millions of people worldwide. Although intravitreal injection can directly deliver drugs to the posterior segment of the eye, it is invasive and associated with serious side effects. The design of drug delivery systems targeting the posterior segment of the eye in a less invasive manner has still been challenging because of various anatomical and physiological barriers. In this review, we provide an overview of the current implant device-based approaches used for treating retinal degenerative diseases. We then offer our perspectives on future directions and challenges that remain for developing more effective device-based therapies for retinal diseases.

Ocular drug delivery targeted by iontophoresis in the suprachoroidal space using a microneedle

Treatment of many posterior-segment ocular indications would benefit from improved targeting of drug delivery to the back of the eye. Here, we propose the use of iontophoresis to direct delivery of negatively charged nanoparticles through the suprachoroidal space (SCS) toward the posterior pole of the eye. Injection of nanoparticles into the SCS of the rabbit eye ex vivo without iontophoresis led to a nanoparticle distribution mostly localized at the site of injection near the limbus and <15% of nanoparticles delivered to the most posterior region of SCS (>9 mm from the limbus). Iontophoresis using a novel microneedle-based device increased posterior targeting with >30% of nanoparticles in the most posterior region of SCS. Posterior targeting increased with increasing iontophoresis current and increasing application time up to 3 min, but further increasing to 5 min was not better, probably due to the observed collapse of the SCS within 5 min after injection ex vivo. Reversing the direction of iontophoretic flow inhibited posterior targeting, with just ~5% of nanoparticles reaching the most posterior region of SCS. In the rabbit eye in vivo, iontophoresis at 0.14 mA for 3 min after injection of a 100 μL suspension of nanoparticles resulted in ~30% of nanoparticles delivered to the most posterior region of the SCS, which was consistent with ex vivo findings. The procedure was well tolerated, with only mild, transient tissue effects at the site of injection. We conclude that iontophoresis in the SCS using a microneedle has promise as a method to target ocular drug delivery within the eye, especially toward the posterior pole.

Assessment of trans-scleral iontophoresis delivery of lutein to the human retina

The efficacy of novel scleral iontophoresis device for in situ delivery of lutein to the human retina was assessed by Resonance Raman spectroscopy (RRS) technique. Eight human donor eye globes were used for experiments, 6 of which underwent trans-scleral iontophoresis delivery of lutein and the other 2 were used as controls. The scleral iontophoresis applicator was filled with liposome-enriched 0.1% lutein solution and the generator's current was set at 2.5 mA and delivered for 4 min. A custom RRS setup was used for detecting lutein in the inner sclera, choroid, retinal periphery and macula of treated samples and controls. Forty minutes after iontophoresis, the inner sclera, choroid and retinal periphery were greatly enriched with lutein (P < .05); no lutein was found in the same ocular regions of non-treated samples. In the same period, the average concentration of lutein in the macula (4.8 ± 1.7 ng/mm² ) of treated samples was 1.3 times greater than controls (3.7 ± 1.0 ng/mm² ; P = .4). Scleral iontophoresis was shown to be effective in delivering lutein to the human retina. Future studies will aim at assessing if this therapeutic strategy is valuable to enrich the macular pigment in human subjects.

Ocular delivery of proteins and peptides: Challenges and novel formulation approaches

The impact of proteins and peptides on the treatment of various conditions including ocular diseases over the past few decades has been advanced by substantial breakthroughs in structural biochemistry, genetic engineering, formulation and delivery approaches. Formulation and delivery of proteins and peptides, such as monoclonal antibodies, aptamers, recombinant proteins and peptides to ocular tissues poses significant challenges owing to their large size, poor permeation and susceptibility to degradation. A wide range of advanced drug delivery systems including polymeric controlled release systems, cell-based delivery and nanowafers are being exploited to overcome the challenges of frequent administration to ocular tissues. The next generation systems integrated with new delivery technologies are anticipated to generate improved efficacy and safety through the expansion of the therapeutic target space. This review will highlight recent advances in formulation and delivery strategies of protein and peptide based biopharmaceuticals. We will also describe the current state of proteins and peptides based ocular therapy and future therapeutic opportunities.