Ophthalmic drug administration
Two of the largest challenges faced when using topicals to treat pathological states of the eye include patient compliance and ineffective absorbance of drugs into the cornea due to short contact times, solution drainage, tears turnover, and dilution or lacrimation.
Together, these two factors drive a need in the field of scientific research and engineering for a way to better deliver drugs to the cornea of the eye while decreasing dosing frequency and demand for patient compliance.
Strategies to achieve a prolonged residence time of drug delivery systems on ocular surface include mucoadhesive and in situ gelling polymers and thiolated cyclodextrins (see thiomers).
[2][3][6] The U.S. Centers for Disease Control and Prevention (CDC) claims that there were "about 41 million contact lens wearers greater than 18 years old in the United States" in 2018.
However, each of these different types of loading techniques results in contact lenses that all have separate physical and chemical challenges when it comes to the sustained release and penetration of specific drugs at the molecular level in regards to the cornea of the eye.
Since contact lenses are used on a part of the body that is important for normal daily functioning (sight) it is critical that scientists take into account the transparency of the lens.
[5] As larger and more drugs/objects are loaded to a contact lens it begins to physically crowd the space available, making it more difficult for light to penetrate and reach the eye.
[5][12] Oxygen permeability is another important feature of all contact lenses and much be optimized to the largest degree possible when creating drug delivery devices for the eye.
[12] In regards to whether silicon-based lenses or SCLs are a better candidate as an ophthalmic drug delivery device is a question that remains unanswered and is not uniformly agreed upon in the scientific community.
[2][3] Conversely, Kim et al. suggest that SCLs are better candidates because they show the possibility to be able to overcome the difficult of oxygen permeability as well as mechanical integrity of the lens.
[6] Oxygen permeability continues to be an extremely important factor in the development of these devices and is one of the main reason that much research is beginning to focus on this area of drug delivery.
[5] Furthermore, Guzman-Aranguez et al. has shown that when using the molecular imprinting method for loading drugs such as ketotifen and norfloxacin into the contact lens, the water content is not largely impacted.
Researchers such as C. Alvarez-Lorenzo have tested (with animal models) and have data which supports that molecularly imprinted contact lenses release drugs in a sustained and long period of time.
The systemic side effects of glaucoma medications such as latanoprost increased heart rate resulting in cardiac arrhythmias, bronchoconstriction, and hypotension.
It is of utmost importance that these drugs stay in the therapeutic window for an extended period of time in order to be fully effective and kill bacteria.
Researchers have gathered data to support the idea that silicon-based contact lenses with ciprofloxacin could release the drug in the therapeutic window for approximately one month.
[5] Ana Guzman-Aranguez et al. also confirmed that the contact lens used also retained important properties such as transparency, oxygen permeability, mechanical strength, and zero-order release pharmacokinetics.
These cells play a role in creating a physical environment that can correctly bend light rays to help project images to the retina of the eye.
[5][12] There have been successful human clinical trials with using SCLs infused with epidermal growth factor (EGF) that showed increased rate of healing of the epithelial cell layer of the cornea.
[5] In order to help combat this issue and be assured that this does not occur in people that will one day be using drug eluting contact lenses, it is important to make sure that this complication is highly investigated.
