Eye drops often provide quick relief to those suffering from minor eye problems such as redness, itching and dryness, but doctors have found that such dollops of medicine do not work very well for more serious conditions such as glaucoma, chronic dry-eye and corneal ulcers. Help may be on the way for those suffering from these or other ocular ailments in the form of a contact lens that sandwiches medicine between two layers of polymer film and administers large doses of medication at constant rates over extended periods.
In lab tests, prototype multilayer lenses have shown they can release ciprofloxacin (an antibiotic often used to treat eye and other infections) for up to 100 days, according to a study published in the July issue of Investigative Ophthalmology and Visual Science by researchers from Children's Hospital Boston, the Massachusetts Eye and Ear Infirmary's (MEEI) ophthalmology department, Schepens Eye Research Institute in Boston, and the Massachusetts Institute of Technology's (M.I.T.) chemical engineering department.
One of the most important roles these contact lenses could play, according to the researchers, is simply getting all of a given medical dose into a patient's eyes. It is not uncommon for as little as 1 percent of eye-drop solution to get into and stay on the eye long enough to be absorbed, they add.
The breakthrough is the suspension of medicine in a layer made from PLGA (poly(lactic-co-glycolic acid)), a biodegradable polymer. PLGA regulates the amount of drugs medication that passes through it at any given time. The more PLGA there is in relation to the medication, the slower the drug it is released, says pediatric critical care specialist Daniel Kohane, director of the Laboratory for Biomaterials and Drug Delivery at Children's Hospital and the project's lead researcher.
The researchers coated the PLGA film with another polymer, poly-HEMA (poly(2-hydroxyethyl methacrylate)), to form the lens. Poly-HEMA is a transparent hydrogel that allows the patient to see as drugs from the degrading PLGA layer leak through it onto the eye's surface. Medicine-dispensing contacts should also serve as an efficient method of preventing potentially dangerous post-op infections, Kohane says.
Kohane and his colleagues, whose work is funded to the tune of about $250,000 annually from the National Institute of General Medical Sciences, are one of several teams investigating the use of layered drug-dispensing soft contact lenses. Researchers at Spain's University of Santiago de Compostela in the March issue of Biomaterials reported on their work developing acrylic hydrogels with an improved ability to carry drugs and maintain controlled release rate. Singapore's Institute of Bioengineering and Nanotechnology in 2004 announced it had developed a permeable polymer lens that could be laden with eye medication for ocular drug delivery. Two of its researchers were granted joint patents for "Drug-Loaded Contact Lenses for Ocular Drug Delivery" in Taiwan (2007) and Singapore (2008).
The concept of a disposable drug-doling contact lens has been kicked around at least since the 1960s, but attempts have ended with lenses unable to regulate drug diffusion well enough, says Joseph Ciolino, an ophthalmologist with the MEEI and another of the project's researchers. Although it is too early to determine how much such lenses might cost, given that they are only now being moved into animal testing, Ciolino says that he and Kohane think animal testing can be completed in a year. "I look at these lenses and think about people with corneal ulcers, and who have to put drops in every half hour, sometimes for months," he says. "That's a cruel punishment." As many as half of glaucoma sufferers do not follow doctors' orders because of the difficulty administering drops, he adds.
One of the key questions that the researchers will have to answer during testing is how well these special lenses will fit on patients' eyes, which vary in shape and size, says Mitchell Cassel, an optometrist and owner of Studio Optix in New York City who says he is familiar with the work being done by Kohane, Ciolino and their colleagues. "Some people have acute sensitivity in the insides of their eyelids, too," Cassel adds.