RECENT ADVANCES in biomaterials and nanotechnology have opened new possibilities for soft contact lenses (CLs) beyond vision correction. One of the most promising developments is the futuristic use of soft CLs as drug delivery devices, which could revolutionize the way medications are administered to the eye.
The human eye is naturally designed to protect itself from foreign substances, and treating ocular diseases traditionally requires the application of topical medications or injections. However, these methods have limitations.
Eye drops have less than 5% bioavailability because much of the drug is washed away by the tear film or drains into the nasolacrimal system, bypassing the ocular tissue itself (Järvinen, 1995). On the other hand, injections can be invasive, carry the risk of endophthalmitis, and are uncomfortable for the patient, making them a less-than-ideal method of drug administration for routine treatments.
Soft CLs offer a compelling alternative by integrating pharmaceutical agents into the lens material, allowing the drug to be delivered gradually and directly to the ocular surface, ensuring a longer contact time, improved bioavailability, as well as diminished dosing frequency (Mobaraki, 2020).
Advancements in Drug-Eluting Contact Lenses
Several innovative techniques are being explored to integrate drugs into soft contact lenses.
1. Molecular imprinting involves creating nanoscopic cavities within the lens polymer that match the size and shape of the drug molecules, leaving high-affinity pockets to achieve drug loading (Gao, 2024). This enables the controlled and sustained release of the drug over an extended period.
2. With nanoparticle embedding, colloidal nanoparticles entrap or encapsulate the drug within the CL matrix to attain better control over its release rate over an extended period of time (Lovrec-Krstic, 2023).
3. The soaking method involves soaking the CL in a drug solution that is then released into the tear film. However, this approach retains the drug poorly and releases it quickly with a sharp decline. Altering the hydrophilic/hydrophobic monomer ratio of the hydrogel CL influences the drug uptake and release kinetics (Xu, 2011).
4. Layer-by-layer coating involves depositing multiple thin layers of drug-loaded polymers onto the CL surface, allowing for controlled diffusion of medication into the eye (Gao, 2024).
Applications
The ability to deliver drugs via CLs holds immense potential for treating various ocular conditions, including the following:
Glaucoma: Drug-eluting CLs could ensure continuous controlled release of intraocular pressure-lowering medications, improving patient compliance and disease management.
Dry eye disease: CLs infused with lubricating agents or anti-inflammatory drugs could provide long-lasting relief compared to artificial tears.
Allergic conjunctivitis: Antihistamine-loaded CLs offer targeted relief from allergy symptoms without the need for frequent eye drops. Etafilcon A CLs with ketotifen were approved by the US Food and Drug Administration in 2022 and provided relief from ocular itching as quickly as 3 minutes after application, with a therapeutic effect that lasts for up to 12 hours (Pall, 2019); these lenses were later discontinued.
Infections and inflammation: Antibiotic or anti-inflammatory drugs could be embedded in CLs for patients who have ocular infections or inflammation, reducing the need for frequent drop administration and ensuring targeted treatment.
The Future
Soft CLs hold great potential as drug delivery systems but face challenges like enhancing comfort, stability, and controlled release without impairing vision, scaling up manufacturing, and ensuring long-term safety. Despite these obstacles, advancements in science and technology promise a bright future, with soft CLs offering efficient, precise, and patient-friendly treatments that could revolutionize ocular care and improve outcomes for chronic eye diseases.
References
1. Järvinen K, Järvinen T, Urtti A. Ocular absorption following topical delivery. Adva Drug Delivery Rev. 1995 Aug 1;16(1):3-19. https://doi.org/10.1016/0169-409X(95)00010-5
2. Mobaraki M, Soltani M, Zare Harofte S, et al. Biodegradable Nanoparticle for Cornea Drug Delivery: Focus Review. Pharmaceutics. 2020;12(12):1232. doi: 10.3390/pharmaceutics12121232
3. Gao D, Yan C, Wang Y, et al. Drug-eluting contact lenses: Progress, challenges, and prospects. Biointerphases. 2024 Jul 1;19(4):040801. doi: 10.1116/6.0003612
4. Lovrec-Krstič T, Orthaber K, Maver U, Sarenac T. Review of potential drug-eluting contact lens technologies. Materials. 2023 May 11;16(10):3653. doi: 10.3390/ma16103653
5. Xu J, Li X, Sun F. In vitro and in vivo evaluation of ketotifen fumarate-loaded silicone hydrogel contact lenses for ocular drug delivery. Drug Deliv. 2011;18(2):150-158. doi: 10.3109/10717544.2010.522612
6. Pall B, Gomes P, Yi F, Torkildsen G. Management of ocular allergy itch with an antihistamine-releasing contact lens. Cornea. 2019 Jun 1;38(6):713-717. doi: 10.1097/ICO.0000000000001911