Retinitis Pigmentosa | Is There Light at the End of the Tunnel?

Retinitis Pigmentosa | Is There Light at the End of the Tunnel?
September 30 15:21 2021 Print This Article

MEDIUM – Rebecca McClung, 30 September 2021:

For most of us, our ability to see is the single most important tool in our toolkit when it comes to navigating the world. We size up our surroundings, cook our food, read books, create art, write music, make, mimic, mold and master our world using sight as the first and fastest way to gather information.

Retinitis pigmentosa has challenged that ability for years.

Long thought of as a rare genetic mutation that results in the breakdown of photoreceptors in the eye, we now know that RP is actually a sort of custom cocktail of inherited genetic mutations that results in the deterioration of sight. For each individual sufferer, that combination of mutations can differ dramatically — so far, more than 50 genes have been identified as involved in the genetic mutations of RP. The sheer number of possible combinations of these genes and their mutations makes the treatment of RP exponentially challenging.

How Does RP Cause Blindness?

Most of us learned about rods and cones in the eyes during our school days. Found within the retina, these photoreceptors are light sensitive cells that allow us to see light, dark and details. About 95% of these cells are rods, while only about 5% are cones. In the early stages of retinitis pigmentosa, each one of those genetic mutations that are the hallmark of RP targets and kills rods, leaving only the cones intact.

While an RP sufferer can still see with just the cones left intact, the loss of rods causes a loss of night vision and peripheral vision, and in a cascading effect, the damage eventually spreads to the cones in the eye. Photoreceptors responsible for the ability to see fine detail and color, as the remaining cones gradually die off, the visual field shrinks, vision becomes tunneled and eventually blindness results.

There is no cure for this inherited disease, but there is hope.

A grim diagnosis for years, RP has been mostly under-researched or passed over for study due to the low number of afflicted — only about 1 in 4000 people worldwide are affected by the disease, although, interestingly, in India that number is dramatically higher, with 1 in 350 suffering from RP. In all, over 1.5 million people suffer from RP around the world.

Research funds have gone to more common diseases like macular degeneration, glaucoma and diabetic retinopathy. Today, however, studies have begun to find clues to new treatments that show promise for RP sufferers, and new technologies offer new methods of replacing or counteracting the loss of vision that has been inevitable until recently.

 

Photo by Erlend Ekseth on Unsplash

On the Horizon

While traditional treatments have focused on teaching coping skills, like using special lenses that magnify central vision, and text-to-speech tools to read emails online or materials aloud, new tech tools and new treatments are finally offering the hope of slowing or even stopping the disease.

Artificial intelligence is aiding in the development of customized doses of vitamin A to slow the progress of RP. Gene therapies, including gene editing, or CRISPR, are in development now that show real promise, including one highly touted clinical trial that actually led to improved vision in participants carrying a specific strain of RP.

On the technological front, new vision-assist glasses are available that help sufferers regain much of their autonomy, along with the ability to accomplish vision centric tasks, like reading, typing, working with tools and more. Implanted electrode arrays are available that work by using a tiny video camera on a pair of glasses to send signals to a processing unit implanted directly onto the retinal surface. The array then transmits low res signals to the front of the retina, allowing the user to see light sources and high contrast areas like doors or windows.

If You Can’t Beat Them all, Go Around — The ‘NAC Attack’

One of the most exciting developments in the entire research history of RP is going into the third phase of clinical trials of a drug being tested at Johns Hopkins Hospital’s Wilmer Eye Institute in Baltimore. Run by Dr. Peter Campochiaro, George S. and Delores D. Eccles Professor of Ophthalmology at the JH School of Medicine, and Director of the Retinal Cell and Molecular Laboratory, the phase III trial is testing the effectiveness of a drug called N acetylcysteine, or NAC.

NAC functions by reducing oxidative stress in the retina. Once the rods within the retina are dead, the retina uses 90–95% less oxygen, resulting in super high levels of unused oxygen bouncing around the retina with the remaining cones. This superfluous oxygen creates toxic by-products which in turn cause oxidation within critical elements of the cones, leading to damage and the cones’ eventual death.

NAC has already been shown to cause some short term improvement in the function of cones within the retina. The goal for this phase of the trial is to show that NAC may also be effective in preserving the cones outright, effectively removing the inevitability of blindness to sufferers of retinitis pigmentosa. Already considered safe by the FDA to treat another condition, the FDA approval process may be accelerated if the results of this trial are good.

Most significantly though, approval of NAC could provide the first-ever drug to treat RP that benefits not just certain combinations of mutations, but ALL sufferers of RP regardless of the mutations that cause the defect in each individual. That alone is cause for optimism, as the grueling task of concocting custom treatments is long, time-consuming and expensive.

There are still 4 years of testing to complete and much work to be done to make NAC avaialble, but now that the eyes of the research world are seeing RP as a beatable disease. With the innovative approach of Dr. Campochiaro leading the way in the ‘NAC Attack’ studies, there truly is light at the end of the tunnel for hundreds of thousands of people living in the dark today.

 

Rebecca McClung
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