This article is more than 5 years old. Information may no longer be current.
Bandage contact lenses have potential as drug delivery vehicles
Drug delivery via contact lens may increase bioavailability up to 50%.
Click Here to Manage Email Alerts
In addition to providing comfort and pain relief from exposed corneal nerves and mechanical protection from the eyelid for newly produced epithelial cells, bandage contact lenses are under development as drug delivery vehicles, according to a physician.
“The cornea has one of the highest densities of nerve endings in the body. We obtain our innervation in the cornea from the long ciliary nerve, which forms the subepithelial plexus, and the cornea sensitivity is 100 times that of the conjunctiva,” Nicoletta Fynn-Thompson, MD, said at Hawaiian Eye 2013.
Bandage contact lenses serve as a protective barrier, allowing new epithelial cells to form and migrate beneath the lens. They provide comfort and pain relief by restricting the contact of the eyelid against exposed corneal nerves, producing a smooth corneal surface and improving vision as the eye is healing beneath the lens, Fynn-Thompson said.
“Essentially, what we’re trying to avoid is the windshield wiper effect from the lid on the anterior surface of the cornea,” she said.
Indications for bandage contact lenses
Therapeutic bandage lenses are useful in treating symptomatic corneas from loosely adherent epithelium, painful erosions, bullous keratopathy, neurotrophic keratopathy and postoperative healing, Fynn-Thompson said.
Bandage lenses promote healing after corneal transplantations, suture exposure, or ablation with PRK or PTK while providing a protective effect.
“We also use them in conjunction with amniotic membrane grafts in patients who have persistent epithelial defect, nonhealing ulcerations, or with thinning or neurotrophic corneas,” Fynn-Thompson said.
Amniotic membranes can be cryopreserved or fresh and sutured in place or inserted with a self-retaining ring, she said.
Vehicles for drug delivery
Fynn-Thompson shared pearls on bandage contact lenses and drug delivery, particularly for patients on long-term therapy.
“The motivating factor for development is that our eye, the cornea in particular, has a very strong bioprotective mechanism that allows low permeability of medicines getting into the eye,” she said. “We know that the tear fluid that drains into the nasal cavity only allows about 1% to 5% of eye drops to be absorbed.”
In order to compensate, she said that viscous drops, gels and ointments have been used, but none have achieved desired results.
Drug delivery via contact lens would limit tear exchange on the corneal surface and increase bioavailability to 50%, she said.
Fynn-Thompson said that commercial lenses deliver drugs in 1 to 2 hours, so there is a need for other means to increase drug-release duration.
An innovative vehicle in the pipeline is nanoparticles, which are small particles that do not cause light scatter or affect vision. Nanoparticles have a high affinity for drugs and decrease the drug diffusion rate, thus allowing extended delivery, she said. Both lidocaine and timolol were encapsulated in nanoparticles and dispersed via bandage contact lens in recent studies designed to look at increasing drug delivery duration, according to Fynn-Thompson.
“Nanoberries” are another approach that extends delivery of multiple drugs through a contact lens with vitamin E, commonly used in silicone hydrogels.
“[Vitamin E] is hydrophobic so it allows a very tortuous, lengthy route for the drug to make it through and out of the contact lens. The benefit is that you can use this for multiple drugs for the contact lens,” she said.
Finally, using a “lock and key” model similar to the interaction between an enzyme and a substrate, molecular imprinting would create cavities in the contact lens with a high affinity for the drug to be delivered, again allowing an increased duration of drug delivery.
“Once the drug is out of the contact lens, you can reload more of the drug into the contact lens,” Fynn-Thompson said.
Besides delivering drugs through contact lenses, Fynn-Thompson said there is the added bonus of correcting vision.
“The baby boomers are comfortable wearing contact lenses. This would be a nice transition for them,” she said. – by Christi Fox