Article

CONTACT LENS DESIGN & MATERIALS

THE ESSENTIALS OF DRUG-DELIVERING LENSES

Did you know that only about 3% of the medication in an eye drop reaches its target tissue (Maulvi et al, 2016)? This is a considerable problem for the patients who have a microbial keratitis that requires a high concentration of medication to achieve maximum therapeutic value or for glaucoma patients who need a sustained dose of medication to control their ocular pressure (Hui, 2017). Although medicated eye drops are effective, many investigators feel that drug-delivering contact lenses (CLs) could result in better outcomes because they have the potential to provide a more appropriate amount of medication while at the same time reducing systemic absorption and decreasing medication application burden (Maulvi et al, 2016).

The Road to Today

The idea to create drug-delivering CLs has long been contemplated, though problems of material technology (e.g., uncontrolled medication release, poor optics, and poor oxygen transmission) have limited their utility (Maulvi et al, 2016; Hui, 2017). Development began by simply soaking currently approved (unmodified) CLs in a desired medication and then applying them to an eye that needed treatment (Hui, 2017). While unmodified CLs are mass-produced and available to most practitioners, they are limited by uncontrolled release of medication and the inability to absorb large therapeutic molecules (Hui, 2017).

Vitamin E Coating Investigators have attempted to improve medication release properties of commercially available CLs by coating them with a biocompatible layer of vitamin E, which can effectively control the release of medications while at the same time retaining the lens’ optical properties and providing ultraviolet protection (Hui, 2017). Nevertheless, the layer of vitamin E increases the CLs’ thickness and limits oxygen transmission through the CL (Hui, 2017).

Molecular Imprinting Modified CL materials, particularly materials created with molecular imprinting, have also been developed to create viable drug-delivering CLs (Hui, 2017). Molecular imprinting is a type of polymerization technology that mixes the medication with monomers that are then polymerized to create a matrix that has medication-shaped pockets; after polymerization, the medication is replaced with new medication, which is released at the desired amount and rate (Hui, 2017). Drug-delivering CLs developed with molecular imprinting likewise have been limited by unacceptable oxygen transmission for extended wear purposes as well as by poor optical quality (Maulvi et al, 2016).

Other Modifications In addition to molecularly imprinted CLs, other modified materials have been created that take advantage of a material’s charge or of slow-release nanoparticles that have been applied to the CL’s surface (Hui, 2017).

Leading to Tomorrow

While drug-delivering CLs have not fully come of age, a growing body of evidence suggests that they have the potential to treat both acute conditions such as microbial keratitis and chronic conditions such as glaucoma (Hui and Wilcox, 2016; Hui, 2017). Although much progress has been made, material advances are still needed before the ideal drug-delivering CL materials will be cleared by the U.S. Food and Drug Administration.

Once created and shown to be effective at treating ocular disease, these materials will also need to be suitable for mass manufacturing and will need to be able to survive the packaging process (Hui, 2017). Likewise, if the CLs are created for daily wear, they will need to be able to withstand overnight storage and a daily cleaning regimen (Ribeiro et al, 2015; Hui, 2017). Overall, it is only a matter of time before the scientific community is able to find the perfect combination for producing a viable CL that is able to deliver medications for treating ocular disease. CLS

For references, please visit www.clspectrum.com/references and click on document #271.