Advanced Solutions for Sustained Delivery of Ocular Therapies

Aging of the global population and the rise of chronic diseases, particularly diabetes, have contributed to an increase in the occurrence of eye diseases, such as glaucoma, keratitis, age-related macular degeneration (AMD), dry eye disorder (DED), and diabetic retinopathy (DR). Pharmaceutical companies have responded with growing investment in the research and development of novel eye treatments and drug delivery systems designed to address key challenges in ocular therapy. Current treatments range from traditional small-molecule and antibody-based drugs to cell and gene therapies and nanoparticle delivery solutions, along with various types of ocular implants and the use of drug-eluting contact lenses (1,2).

One area of focus has been the development of solutions for the sustained delivery of treatments, particularly to the posterior part of the eye. Many ocular therapies are formulated as eye drops that must be administered frequently to overcome the many physical and mechanistic barriers in the eye and ensure sufficient dosing. Sustained and targeted delivery products are helping reduce the dosing frequency by overcoming ocular barriers and increasing bioavailability.

Anterior delivery challenges

Delivery of therapeutics to the anterior, or front of the eye, is generally simpler than delivery to the posterior part, because topical eye drops are an option. There are limitations to their effectiveness, however. “Drops do not maintain good bioavailability and are relatively quickly flushed out by nasolacrimal drainage,” explains Jeffrey S. Heier, chief scientific officer with Ocular Therapeutix. “While they are a convenient mode of delivery,” he adds, “they present challenges in terms of not only bioavailability, but limited duration of therapeutic effect, both of which contribute to inconsistent patient compliance and suboptimal outcomes.”

Treatments for glaucoma (high eye pressure), as well as infections and inflammation of the eye, are good examples. Glaucoma eye drops typically need to be administered at least once daily, and in many cases, multiple times a day. For some conditions, Heier observes, drops must be delivered on an hourly basis. “Such a dosing frequency is only sustainable for a short period of time. In fact, it is readily accepted that even with easy-to-administer options like eye drops that must be applied just once daily, adherence remains a major issue due to the frequency of this regimen,” he says.

Another option for treatment of the anterior segment of the eye is straightforward intracameral injections, according to Heier. This method of administration delivers ocular therapies directly into the anterior chamber of the eye, allowing for targeted delivery and resulting in enhanced bioavailability (3).

While treatments for infection, inflammation, high eye pressure, and neovascularization have been shown to be effective, this method of delivery is considered “off-label,” as FDA has not approved products specifically for this use, except two intracameral implants (see below). In addition, many patients are hesitant to receive eye injections.

Posterior delivery even more difficult

Targeting the back of the eye presents unique challenges, not only in achieving therapeutic durability but also in navigating complex regulatory expectations, Heier comments. Indeed, delivery to the posterior segment is anatomically more complicated, especially when the durability of treatment is a primary objective.

“Although advances in intravitreal medicines have shown incremental increases in durability compared to prior standard of care, current retinal therapies rely on frequent intravitreal injections to maintain their effect,” observes Peter Jarrett, chief technical officer for Ocular Therapeutix.

For many patients, even therapies that require administration every three to four months can be challenging, as this type of regimen places a significant burden on patients and care partners, according to Jarrett. “To treat the full spectrum of patients with retinal disease or other conditions affecting the posterior segment, there is still a need for more durable treatments, and the development of longer-lasting treatments is such a critical focus,” he says.

New sustained-delivery therapies, however, must be proven to be as safe and effective as existing treatments that may require much more frequent administration. In addition, Jarrett notes that targeted delivery to the retina and posterior segment of the eye necessitates overcoming several blood-ocular barriers, including the blood-aqueous barrier and the blood-retina barrier.

“Historically,” Jarrett explains, “overcoming these physiological defenses has required delivering drugs at high concentrations. However, this approach often results in increased systemic exposure, which in turn can lead to a higher incidence of adverse events and toxicities. Striking the right balance between effective ocular delivery and systemic safety remains a focus in the development of retinal therapies.”

Potential for better treatments with greater convenience

While small steps taken to enhance ocular delivery have had positive impacts, there is still real potential for innovative solutions, particularly those leveraging sustained-release delivery technologies, to have dramatic effects on patient outcomes.

“While incremental improvements can be achieved through sophisticated formulations, such as enhancing solubility, prolonging ocular surface retention, or improving penetration through ocular barriers, these refinements often reach a ceiling in terms of clinical impact,” Heier remarks. “In contrast, transformative advances in treating chronic eye diseases are more directly realized through sustained-release delivery technologies, which bypass many of the pharmacokinetic limitations of topical or injectable drugs by providing continuous, controlled delivery of therapeutics directly to targeted intraocular tissues over extended periods,” he contends.

In addition, Jarrett emphasizes how important it is for developers to realize that results obtained in clinical trials often do not translate to the real world for treatments with dosing regimens patients have difficulty consistently maintaining as part of their daily lives. “A durable therapy that reduces treatment burden could offer not just convenience, but potentially better long-term outcomes for patients who would otherwise fall through the cracks of an intensive treatment schedule. Recognizing this balance between ideal clinical trial conditions and the real-world experience of patients is key to advancing more durable treatment options,” he states.

Nanoscale enablers of sustained delivery

Nanoscale drug-delivery systems are recognized to achieve enhanced bioavailability and targeted and sustained delivery of many types of therapeutics addressing a wide variety of conditions, including eye diseases (2). Examples of different types of nanoparticles used for ocular drug delivery include nanomicelles, liposomes, polymeric nanospheres, and peptide-based nanoparticles (2).

Nanomicelles in preclinical testing have been shown to experience good uptake by corneal cells and when administered topically to achieve sustained delivery of drugs to treat DED, neovascular AMD, inflammation, and other eye disorders (1). Biocompatible lipid nanoparticles can deliver drugs with both hydrophobic and hydrophilic properties for extended periods. In one animal model of glaucoma, large unilamellar liposomes achieved sustained delivery of latanoprost, a common drug used to reduce eye pressure, for up to five days (4).

Peptide-based nanoscale delivery systems are particularly attractive because they are not only biocompatible, but can be used to target specific cell receptors, disrupt endosomal membranes, and carry drug payloads to the nucleus (1). Of the two main types of systems (elastin-like polypeptides and silk fibroin polymers), the former have been investigated for sustained release of drug substances from contact lenses due to their ability to remain adhered to their surfaces.

Researchers continue to investigate the potential of nanoscale materials for the formulation of extended-release ocular therapeutics, with efforts focused on increased drug-loading capacity, ocular residence time, and release periods while reducing potential toxicities (1).

Drug-eluting contact lenses and canalicular plugs

Given the limitations and issues associated with the use of eye drops and intracameral injections for treatment of conditions in the anterior segment of the eye, other options for delivery are looking to leverage the accessibility of this portion of the eye, according to Heier. Examples include drug-eluting contact lenses and canalicular plugs.

As indicated previously, sustained, topical delivery of ocular therapies to the anterior of the eye is possible using contact lenses loaded with active drug substances, such as peptide-based nanoparticles carrying drug payloads. It is even possible to improve drug loading by incorporating non-covalent binding sites into the lenses when they are manufactured (1). Delivering drugs using contact lenses is attractive because this approach is non-invasive and can potentially support increased drug uptake compared to topical applications (eye drops, creams, ointments). ACUVUE Theravision contact lenses (Johnson & Johnson Vision Care), which provide sustained delivery of ketotifen for the treatment of itchy eyes, are the first FDA-approved drug-eluting contact lens product (5).

Canalicular plugs belong to a class of treatments known as punctal plugs, which are inserts designed to slow or block the outflow of tears from the eye (6). Punctal plugs can be temporary, semi-permanent (resorbable), or permanent (synthetic, usually silicone), and some are able to provide sustained release of drug substances. They are most widely used to treat DED and have been shown over three decades to be generally safe and effective; although, they can fall out, become partially displaced, or lead to watery eyes.

Recent developments have helped address many of these issues. One example is a canalicular gel device (Lacrifill, Nordic Pharma) introduced in June 2024 (7). The chemically crosslinked particulate hyaluronic acid (HA) hydrogel device is designed to completely fill the canaliculus regardless of its size in different patients, preventing dislodgement and the buildup of stagnant tears and mucus that can result in infection. It is meant to be used for up to six months and can be easily removed by applying a sterile solution.

Ocular implants

Significant advances have also been made over the past two decades in ocular implant technology for sustained release of drugs that treat a number of eye diseases. Implants can be biodegradable, although some are not (8). The former can suffer from the rapid release of remaining active drug substance upon degradation, while the latter require surgical removal when the drug substance is fully released.

Bioerodable implants are thus receiving more attention. These products are slowly solubilized upon exposure to biological fluids, leading to slow release of the drug and absorption of the implant material into the eye, avoiding a final “burst” release (8). The rate of dissolution can also be controlled by modifying the chemical composition of the polymer used in the implant. Theoretically, these devices could provide sustained release of therapeutics for months to years.

Jarrett highlights the use of degradable or erodible matrix materials for the sustained delivery of small-molecule drugs. “The choice of drug and implant material are extremely important in designing such a sustained-release system,” he says. “Challenges include drug potency, safety, control of drug release rate, local and systemic drug concentrations, implant biocompatibility and bioresorption, implant size and placement position, and the injection technology utilized,” Jarrett denotes.

As an example, Jarrett points to bioresorbable hydrogel technology as offering a long-term option for delivering small molecules to the posterior segment. Hydrogels, he says, are well-suited to deliver extremely low solubility, lipophilic drugs because the release rate is being controlled by drug solubility. “Drug solubility in both the hydrogel matrix and in the vitreous humor fluid are important rate control factors. These factors may be combined to create a constant release rate in the eye,” he explains.

In addition, the bioresorbable hydrogel vehicle can be designed to break down into water soluble molecules that are neutral pH, non-reactive, and readily cleared from the eye, with timing of resorption tailored to synchronize with drug depletion, allowing repeat injections without crowding the vitreous with empty vehicles or “shells” from earlier injections.

Implants have, in fact, been developed for insertion into both the anterior and posterior segments of the eye. The devices are either implanted surgically or via injection (intracameral for anterior and intravitreal for posterior applications). Injected implants are typically smaller as they must be able to fit into a needle (7).

Two examples of FDA-approved intracameral implants are Durysta (Allergan) and iDoseTR (Glaukos), both of which provide sustained release of drugs (bimatoprost and travoprost, respectively) to treat intraocular pressure in open-angle glaucoma/ocular hypertension.

There are also several intravitreal implants approved by FDA, including Ozurdex (AbbVie) for macular edema and Dexycu (EyePoint Pharmaceuticals) for post-operative inflammation. Encelto (Neurotech Pharmaceuticals), which leverages an encapsulated cell therapy technology to continually deliver therapeutic doses of ciliary neurotrophic factor to the retina to treat macular telangiectasia type 2, received FDA approval in early 2025 (9).

FDA approval was also granted in early 2025 to Susvimo (Roche) for the treatment of DME, which continuously delivers ranibizumab via the Port Delivery Platform, a refillable (every six months) eye implant surgically inserted into the eye (10).

Continued developments anticipated

While there remain many challenges to effectively treating diseases of the eye, significant strides have been made with recent advances in technologies supporting sustained, targeted release of effective ocular therapies. With many additional, innovative solutions in preclinical through late clinical development, additional progress is expected.

References

1. Whalen, M.; et al. Seeing the Future: A Review of Ocular Therapy. Bioeng. 2024 11 (2), 179. DOI: 10.3390/bioengineering11020179
2. Chandel, A. and Kandav, G. Insights into Ocular Therapeutics: A Comprehensive Review of Anatomy, Barriers, Diseases, and Nanoscale Formulations for Targeted Drug Delivery. J. Drug Del. Sci. and Tech. 2024 96. 105785.https://doi.org/10.1016/j.jddst.2024.105785
3. Gautam, M.; et al. Intracameral Drug Delivery: A Review of Agents, Indications, and Outcomes.J. Ocul. Pharmacol. Ther.2023 39 (2), 102-116. DOI:10.1089/jop.2022.0144
4. Natarajan, J.V.; et al. Sustained Release of an Anti-Glaucoma Drug: Demonstration of Efficacy of a Liposomal Formulation in the Rabbit Eye. PLoS ONE 2011 6, e24513.
5. Johnson & Johnson Vision. Johnson & Johnson Vision Care Receives FDA Approval for ACUVUE® Theravision™ with Ketotifen - World's First and Only Drug-Eluting Contact Lens. Press Release, March 2, 2022. https://www.prnewswire.com/news-releases/johnson--johnson-vision-care-receives-fda-approval-for-acuvue-theravision-with-ketotifen--worlds-first-and-only-drug-eluting-contact-lens-301493964.html
6. Cleveland Clinic. Punctal Plugs. ClevelandClinic.org (accessed June 20, 2025). https://my.clevelandclinic.org/health/treatments/25249-punctal-plugs
7. Charters, L. New Canalicular Gel Shows Promise for Dry Eye Treatment. Ophthalmol. Times2024 49 (11). https://www.ophthalmologytimes.com/view/new-canalicular-gel-shows-promise-for-dry-eye-treatment
8. Wykoff, C.C.; Kuppermann, B.D.; and Saïm, S. Extended Intraocular Drug-Delivery Platforms for the Treatment of Retinal and Choroidal Diseases. J. VitreoRet. Dis. 2024 8 (5). DOI:10.1177/2474126424126706
9. Neurotech Pharmaceuticals. Neurotech’s ENCELTOTM (revakinagene taroretcel-lwey) Approved by the FDA for the Treatment of Macular Telangiectasia Type 2 (MacTel). Press Release, March 6, 2025. https://www.neurotechpharmaceuticals.com/wp-content/uploads/Neurotech_Press-Release_BLA_Approval_FINAL.pdf
10. Roche. FDA Approves Roche’s Susvimo as the First and Only Continuous Delivery Treatment for the Leading Cause of Diabetes-related Blindness. Press Release, Feb. 3, 2025.https://www.roche.com/media/releases/med-cor-2025-02-04#:~:text=Susvimo%C2%AE%20(previously%20called%20Port,edema%20(DME)%20that%20continuously%20delivers

About the author

Cynthia A. Challener, PhD, is a contributing editor for Pharmaceutical Technology®.