The retina—the thin, fragile layer of tissue lining the back of the eye—gives us the invaluable gift of vision. It works like film or digital sensors in a camera by converting the light that enters our eye into electrical signals. Those signals are sent over the optic nerve to the back of the brain, where they are used to create the images we see.
The retina is an extension of the brain. Like the brain tissue inside our skulls, the retina is comprised of neural cells. This fact is highly significant because it means that a drug or biological therapy that helps save retinal cells in a person with a retinal degenerative disease like retinitis pigmentosa (RP) or macular degeneration might also preserve cells in the brain of someone with a neurodegenerative condition such as Parkinson’s, Alzheimer’s or multiple sclerosis.
For researchers developing treatments for neurodegenerations, the retina is often a better target for testing and evaluating potential therapies than tissue inside the skull would be. First and foremost, the retina is much more accessible than the brain, because it’s a small piece of tissue and is located outside of the skull. Also, because people have two retinas, one in each eye, scientists can treat one retina and compare the effect of a therapy—for example, a change in vision—to the untreated retina. Last, because the retina is relatively isolated, there is less chance of collateral damage if an emerging therapy has unwanted effects.
Retinal research is moving at an incredible pace. Just 10 years ago, there were few therapies in clinical trials. But, today, dozens of drugs, gene therapies and stem-cell treatments for retinal degenerative diseases are now moving into and through human studies. Some are even restoring vision to people who are blind.
The retinal-disease gene therapy for RPE65 gene mutations being developed by Spark Therapeutics—and made possible by decades of Foundation-funded research—is in good position to be approved by the U.S. Food and Drug Administration (FDA). Researchers studying brain and neural diseases closely monitor the success of retinal researchers, because it gives them clear, attractive targets for therapy development.
Optogenetics is a prime example of a promising, emerging therapeutic technique that shows great potential for conditions that affect the retina, brain and central nervous system. It works by bestowing light sensitivity to neural cells. In the retina, the approach shows promise for restoring vision to someone who is otherwise completely blind. By bestowing light sensitivity to the brain, researchers hope to use light to activate neural cells to restore function to someone with a neurodegenerative disease (e.g., Parkinson’s), depression or even a sleep disorder.
RetroSense, a start-up biopharmaceutical company in Michigan that’s been supported by the Foundation, recently received FDA authorization to launch a clinical trial of its optogenetic therapy for people who are blind from RP. If the study is successful, the company hopes to use it for people with macular degeneration as well.
Stay tuned to Eye on the Cure and the Foundation’s website for updates on emerging retinal-disease therapies, including those that may bolster development of treatments for the brain.
Brain image, above, courtesy of the National Institute of General Medical Sciences.