By David Warmflash
Management of glaucoma depends on the application of agents directly to the eye to lower intraocular pressure (IOP). Although available drugs are highly effective in controlling IOP and preventing blindness, generally the drugs are applied in the form of eye drops. For optimal efficacy, drops need to be instilled correctly, with strict adherence to a fairly rigid schedule, a scenario that often does not lend itself to good patient compliance. This highlights the need for new drug delivery approaches, particularly those that deliver the drug without the patient having to do much, or systems that reduce the number of drug administrations that are needed throughout the day.
One novel delivery system uses a contact lens as the dispensing device. While it sounds exotic, the idea actually has been around for about 50 years, but is becoming a reality now because of advances in materials science. According to researchers exploring the technology at Harvard Medical School, MIT, and several other Boston centers, latanoprost-polymer films (used commonly in lens hydrogel) are encapsulated in a process that creates a clear central aperture, the periphery of which is made to hold a drug-polymer film. This allows the drug to be released gradually into the eye.
Two years ago, a study at Case Western Reserve University looked at effects of the system on IOP in beagles, using extended-wear contact lenses loaded with timolol, a beta andrenergic blocker frequently given for glaucoma. In addition to the control condition in which timolol was administered as standard drops, lenses were either kept in the eye for four days straight, or replaced once per day. Although IOP reduction occurred both for the drops and the day-to-day lens protocol, the latter scenario achieved the effect at 1/5th the dose of the drop method. Additionally, the researchers found that adding vitamin E made the four-day method effective as well.
When considering these results, we should keep in mind that “compliance” with the drop method was optimal, since the dogs were given the medication on the appropriate schedule. For people, who have to use the drops themselves (or with assistance of a relative or friend),compliance often is not optimal. While patients may have even more trouble inserting the contact lenses and replacing them, this drawback seems less troublesome if we consider the four-day replacement protocol. In or out of medicine, once a certain technology has been developed, it improves rapidly. Just thinking about early contact lenses that were enormous and rigid, most modern contact lens wearers would cringe. But we all know how quickly the innovations came, and today, there are contact lenses that can be worn for a week or more. Extending this idea to lenses that dispense drugs, we can anticipate lenses dispensing medication for much longer than four days before they need to be replaced. With such an extended schedule, anybody uncomfortable changing the lenses themselves could have it done in the setting of the doctor’s office, making compliance optimal as with the dogs in the lab.
With current designs, drug-dispensing contact lenses are not made to provide any refractive power. The purpose is drug administration only, so those needing refraction correction would have to wear regular eyeglasses at the same time. But that of course is a minor issue. All in all, because compliance with eye drop medication for glaucoma is notoriously low, novel delivery systems like this one stand to improve the management of eye conditions substantially.