Contact lenses could be used to deliver drugs to treat eye diseases like glaucoma, researchers say.
The team from the University of Florida say they have been able to make soft contact lenses which can slowly release drugs directly into the eye.
The lenses could also be made to correct vision problems.
It is hoped the lenses could replace eye drops, which are often difficult to use, mixing with tears and running down the face instead of going into the eye.
If drugs do drain into the nasal cavity and then into the bloodstream and to other organs, they can cause serious side effects such as heart problems.
Because of the process in which the drops are given, there may initially be an “overdose”, declining to levels too low to have an effect.
Drugs in a contact lens could be released slowly enough to stay in the eye, the researchers say.
Even antibiotics could be delivered through the lenses, making wearers less vulnerable to bacterial infections than they are with normal lenses.
Eye experts estimate around a quarter of a million people in the UK have glaucoma, but only half are diagnosed.
The researchers have been able to encapsulate drugs in nanoparticles, tiny particles which cannot be seen by the naked eye.
The nanoparticles can be mixed into the contact lens matrix during manufacture.
The lenses could be worn for up to two weeks, delivering the right amount of drug at the right time direct to the eyes.
The researchers say when the contact lenses are placed on the eye, the drug diffuses from the particles, travelling through the lens matrix, and into the thin film present between the film between the cornea and the lens.
The drugs remain in the film for much longer than drugs delivered via drops, which remain there for about two minutes.
Being present for longer means drugs are delivered directly into the eyes and does not go into the bloodstream.
Other researchers have tried to develop contact lenses which can deliver medication by soaking them in a drug solution or trapping the drug in a hollow cavity between two pieces of lens material.
But the researchers behind this latest development say, in tests, those methods often only work for a short period.
Dr Anuj Chauhan, who led the research said: “One of the biggest problems with using eye drops to deliver medication to the eyes is that about 95% of the medication goes where it’s not needed.
“Our approach allows us great flexibility in designing controlled drug delivery vehicles that can be tailored to different drugs, but are also effective for extended periods of time.”
He added that the lenses were only in the design stages and have not yet been tested clinically.
A spokesman for the Royal National Institute for the Blind told BBC News Online: “This type of direct delivery system is already used in the treatment of conditions, such as nicotine replacement patches.
“If pharmacologists and researchers are able to devise a way for this to be used successfully in the treatment of glaucoma, then that is good.”
He added: “The RNIB welcomes all scientific advances that lead to improvements in the treatment of eye conditions, but we do stress that this research is currently at a very early stage.”
The research was presented to the American Chemical Society meeting in New Orleans.
Revision date: July 6, 2011
Last revised: by Amalia K. Gagarina, M.S., R.D.