Researchers take a fresh look at conventional eye drops

Imagine not having to use daily eye drops for chronic dry eye and other anterior segment diseases. Researchers in Canada did.

Researchers have developed and tested tiny polymer-coated, medication-delivering packets in rats. Those packets (called micelles) are applied to the wet surface of the eye. In their study, the packets gradually dissolve over a two-week period, releasing medication to treat dry eye and other eye diseases, and make the daily application of eye drops unnecessary.

Heather Sheardown, Ph.D., professor of chemical engineering, and other researchers at McMaster University in Hamilton, Ontario, presented on the packets in mid-September at the 8th International Conference on the Tear Film & Ocular Source: Basic Science and Clinical Relevance, in France.

Their study, "Phenylboronic-Acid-Based Polymeric Micelles for Mucoadhesive Anterior Segment Ocular Drug Delivery," was published in Biomacromolecules earlier this year.

"Mucoadhesive micelles offer significant potential to increase the bioavailability of topically applied ophthalmic drugs," the researchers write in the conclusion of their study. "This will help to decrease the dosage, frequency of dose, and off-target systemic toxicity that are commonly associated with topical pharmacologic drops."

"It's a novel delivery mechanism for enhancing drug absorption through the ocular surface," says A. Paul Chous, O.D., optometric representative to the National Diabetes Education Program of the National Institutes of Health, who practices in Tacoma, Washington.

The study

According to researchers, eye drops are commonly used because they are inexpensive, easy to apply and non-invasive. Unfortunately, they aren't the most efficient and effective treatment option for patients.

Only 5% of a dose reaches the anterior tissues of the eye, where it will do the most good, the study's researchers say.

"The volume of tears that can be accommodated by the cul de sac of the eye is approximately 7 microliters while the volume of a typical drop is 30 microliters," Dr. Sheardown says. "That immediately leads to a significant loss. As well, the tears quickly dilute any drop that is put in the eye, as a protective mechanism, leading to even more losses.  

"Finally, the cornea itself provides a further barrier to the medication actually getting inside the eye," she adds. "This leads to a loss of as much as 95%."

Enter the researchers who work in the area of drug delivery. They developed the imperceptibly small packets. The eyes are responding well in preclinical testing in animals, Dr. Sheardown says.

"The packets were designed to take advantage of the natural properties of the tears and the ocular surface," she says. "This means that we can overcome some of the natural protective mechanisms of the eye and allow for longer periods of time between the instillation of drops, as well as allowing lower concentrations of drug to be in the tear film at any time." 

Great potential

It's a patient-friendly way of delivering medicine, says Dr. Chous, who noted that it will potentially provide another treatment option for doctors of optometry to offer their patients.

"An aggregate of insoluble drug molecules in solution (a colloid) was developed to form micelles (similar to surfactant cleaners) with mucoadhesive properties, allowing dramatically enhanced contact time with corneal epithelial cells and facilitating drug entry with much lower concentrations and over an extended period of time," Dr. Chous says. "Early measures of safety (minimal or no drug toxicity) were demonstrated in vitro and in an animal model.

"The potential is great for conditions requiring repetitive administration of eye drops to treat glaucoma and retinal vascular disease (e.g., anti-VEGF agents for age-related macular degeneration or diabetic macular edema), particularly as the possibility of systemic adverse reactions from high concentrations of drug through intravitreal absorption or via the nasolacrimal duct with vascular absorption are greatly reduced," he adds. "In essence, this technology might allow any pharmaceutical agent to have all the benefits of a 'prodrug,' without having to engineer the conversion of inactive molecules into active molecules, once the corneal barrier is crossed."

The AOA follows all research closely, including potential treatments for dry eye and other eye diseases; however, research is continuing on this novel drug delivery option. For more information or help for better vision, please visit the  AOA website.