Using Microneedles To Deliver Drugs to the Retina: Helpful for Macular Degeneration?
by Maureen Duffy
Using a Microneedle for Drug Delivery to the Posterior Segment of the Eye was published in the July 2012 issue of Investigative Ophthalmology & Visual Science, the official journal of the Association for Research in Vision and Ophthalmology (ARVO).
ARVO is an international organization that encourages and assists research, training, publication, and dissemination of knowledge in vision and ophthalmology, including low vision.
The authors are Samirkumar R. Patel, Damian E. Berezovsky, Bernard E. McCarey, Vladimir Zarnitsyn, Henry F. Edelhauser, and Mark R. Prausnitz, representing the following institutions: the Georgia Institute of Technology and Emory University School of Medicine, Atlanta, Georgia.
About the Study and Some Terminology
The objective of the study was to determine whether injection into the suprachoroidal space using a microneedle (with an animal model) offered a simple and minimally invasive way to target the delivery of injectable drugs, such as Avastin and Lucentis for macular degeneration, to the posterior segment of the eye.
Here are some definitions that can help explain and interpret this research:
- The posterior segment is the back two-thirds of the eye that includes the vitreous humor, retina, choroid, and optic nerve.
- The choroid is a dark brown membrane that is rich with blood vessels, located between the sclera and the retina. It supplies blood and nutrients to the retina and nourishes all of the other structures within the eye.
- The sclera is a tough white outer coating of fibrous tissue that covers the entire eyeball (all the way around) except for the cornea. The muscles that move the eye are attached to the sclera.
- The suprachoroid, which is the injection site used in the study, is the thin, outermost layer of the choroid that lies against the sclera.
- The microneedles used in the research are stainless steel and less than one millimeter long. The researchers hypothesized that microneedles would cause less trauma to the eye than the larger hypodermic needles currently used with injectable eye drugs and reduce the risk of infection.
The injectable materials/substances included fluorescein, glucose molecules, Avastin (bevacizumab), and polymers, or polymeric particles. Fluorescein is an orange dye that is injected intravenously (usually in the arm). Ultraviolet light makes the fluorescein dye "light up" as a fluorescent yellow-green color and allows doctors and researchers to observe the path of blood flow within the eye.
The Study Results
The researchers demonstrated that microneedles can deliver drug molecules and particles to the eye in an animal model. The study revealed that the concentration of injected substances was at least ten times greater in the back of the eye tissues than in the tissues at the front of the eye, which is extremely helpful when targeting or treating macular degeneration and other diseases of the retina.
The study also showed that injections of fluids into the suprachoroidal space can reach the targeted parts of the eye and remain there for extended periods of time; in addition, the injected substances did not significantly reach the lens or the front part of the eye, where side effects from drugs can occur.
From a Newswise.com press release:
"The study showed that if we inject non-degradable particles into the suprachoroidal space and wait as long as two months, the particles remain," said [study author] Mark Prausnitz. "That means there is no natural mechanism to remove the particles from the eye. Knowing this, we can design biodegradable particles with drugs encapsulated in them that can slowly release those drugs over a period of time that we could control."
"This research could lead to a simple and safe procedure that offers doctors a better way to target drugs to specific locations in the eye," said Samirkumar Patel, the paper's first author … "The design and simplicity of the microneedle device may make it more likely to be used in the clinic as a way to administer drug formulations into the suprachoroidal space that surrounds the eye."
The next step in the study will examine how efficient the microneedle technique is moving real drugs to the necessary eye structures. VisionAware will provide updates of this important research as they become available.
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