The Coming Rise of Drug-delivery Contact Lenses

This novel new system could mark a significant advancement for eye care.

By Melissa Barnett, OD

The use of contact lenses as ocular drug delivery systems was first introduced as an idea decades ago. As contact lenses have advanced, the once-futuristic thought of drug-delivery contact lenses is now becoming a reality. This article discusses how improvements in contact lenses have helped pave the way for a new wave of drug delivery systems.

Background

We are well aware that visual impairment and ocular disease are highly prevalent worldwide and can be debilitating. According to the National Eye Institute, the estimated number of people affected by the most common eye diseases will double between 2010 and 2050.1 These conditions include diabetic retinopathy, glaucoma, age-related macular degeneration and cataracts. Modern treatment modalities for ocular disease range from conventional liquid eye drops and ocular medications to invasive injections in the vitreous and surgical procedures to the removal of damaged areas and implant devices.2-4

Eye drops have traditionally been the standard method for delivering medications to the eye. Unfortunately, a major disadvantage with eye drops is their low bioavailability of less than 5%.5 That’s not all. A landmark review illustrated that eye drops are associated with a pulsatile delivery, with a wide range of tissue concentrations.6 This variability is undesirable, particularly in the case of chronic treatment of glaucoma with molecules of short duration of action. Eye drops for long-term use come with the same risk associated with any chronic patient-administered medication, requiring treatment adherence.

With respect to the application of drops, patient adherence to therapy is impacted by a variety of issues, including drug cost, accessibility, availability, regimen, convenience, iatrogenic discomfort or irritation, dropper tip contamination and side effects.7 At times, poor communication or understanding of why the medication is recommended is the culprit of nonadherence.8 Equally as important is proper instillation of eye drops, which is only correctly performed by a smaller subset of patients.9-11 Systemic disease such as advanced rheumatoid arthritis, poor dexterity, tremor, reduced grip strength, loss or deformity of digits and poor aim may make eye drop instillation difficult and bring about product waste.

Eye drops tend to have excessive volume since one dose is usually 20µL to 50µL, larger than the precorneal space of approximately 7µL.12 Typically, approximately only 1% to 5% of applied drug is absorbed into the eye.13 Ocular drug delivery systems are designed to overcome the limitations of eye drops in various ways, including extended residence time, decreased pulsatile delivery, controlled delivery and enhanced local delivery to the posterior segment.

The application of scleral lenses as drug delivery devices has been illustrated with the advantage of a large fluid reservoir. Scleral lenses provide a protected environment in which the corneal surface is continuously bathed in preservative-free fluid. These lenses are inherently stable to provide lasting ocular penetration of a drug. The main detriments of scleral lenses include handling and cost.14

Various publications have reported the use of scleral lenses as ocular drug delivery systems. Specifically, corneal infiltrates have been treated with topical fortified preservative-free antibiotics in the bowl of the lens.15 Preservative-free antibiotics in the bowl of a continuously worn scleral lens have helped treat persistent epithelial defects.16 Anti-VEGF agents have been used in the bowl of a scleral lens to treat corneal neovascularization.17,18 In addition, stem cells on a scleral lens carrier have been used in the management of chemical burns in an animal model.19