A new method to deliver therapy to the eyes using tiny needles coated with drugs could offer a better way to treat people with diseases such as glaucoma, macular degeneration and diabetic retinopathy — thus, avoiding complications associated with current intraocular injections and systemic administration of drugs.

"The concept of microneedles existed a long time ago," Samirkumar Patel, a researcher at Georgia Institute of Technology (Atlanta) told Medical Device Daily. "There were patents filed in the 1970s on this idea, that you could use tiny needles to create pathways into tissues to allow drugs to diffuse across a given tissue faster. But they were primarily designed for use on the skin."

Patel is part of a team that includes researchers from Emory University (Atlanta) who are working to exploit this concept for new therapeutic applications.

"Our group at Georgia Tech designed and fabricated these microneedles in the 1990s," Patel said. "The reason they didn't exist until then is because the technology didn't exist to fabricate them at that [micro-sized] scale. We decided to branch out of transdermal delivery and started looking to deliver drugs into the eye, which is a completely new idea."

The solid metal microneedles, measuring 500 to 750 micro-millimeters in length, are used to penetrate the eye but go only as deep as a half-millimeter into the tissue. This means that the needles do not penetrate far enough to cause as much damage — such as retinal detachment — as traditional needles. As a result, they can be applied to the eye using only local anesthetic.

Traditional ocular drug delivery methods, such as eye drops, don't efficiently reach the back of the eye. Injections with even the smallest standard hypodermic needles are unacceptably invasive because the needle penetrates across eye tissues. And repeated injections with regular needles can result in complications to vision.

Patel said, "With eye drops, only 1% to 3% of the drug actually gets into the front portion of the eye. It's a very low percentage for drug delivery efficiency. For older people who have serious vision issues, the drug needs to be delivered to the back of the eye and these injections are not one-time treatments. They are typically done multiple times over four to eight weeks.

"It's very invasive and repeated injections can cause complications."

By using the tiny needles, drugs can be delivered locally, minimizing the amount of drugs used and reducing side effects and costs, according to Patel.

"And, what you deliver can be designed to stay longer in the tissues and eventually diffuses into the retina," he said. "The microneedle has versatility to deliver drug to different parts of the eye. Now they just try to get it into the eye and hope it reaches the target. With the microneedle, you can selectively deliver to a region of the eye."

"So far, tests indicate the microneedles showed very little reaction from rabbits," Patel said. "In visual tests done within a matter of hours after delivery, you couldn't tell that anything happened."

Research on this method of ocular drug delivery is at a very early stage, the team so far working with eyes from cadavers and rabbits.

Patel predicts that it will be about five more years until the microneedles are ready for human clinical trials.