Study shows partial vision re-stimulation in a patient with Retinitis pigmentosa.
Retinitis pigmentosa (RP) is a rare, inherited degenerative eye disease that causes severe vision impairment. Early symptoms may include decreased night vision and tunnel vision. Retinitis pigmentosa affects an estimated 2 million people around the world and is typically diagnosed in childhood or adolescence. However, it can take years for an individual’s vision loss to become so severe that they are, more or less, blind. There are certain medications that treat complications, but so far, there has been no proposed “cure.” Now, a recent study by a team of researchers led by Dr. José-Alain Sahel, professor of ophthalmology at Sorbonne University and the University of Pittsburgh, and published in Nature Medicine, has reported a simple yet effective way to restore partial vision.
The authors write, “more than 70 genes cause deterioration of the rod-shaped photoreceptors that principally govern peripheral vision and the cone-shaped receptors,” leading to Retinitis pigmentosa. Essentially, the retina quits working as it should. However, “Optogenetics may enable mutation-independent, circuit-specific restoration of neuronal function in neurological diseases.”
The team used ChrimsonR, a protein that opens electrical channels in neurons and makes them reactive to light, as well as a genetically manipulated, benign adenovirus to carry ChrimsonR when injected into the fluid-filled portion of the eye behind the lens. “The ChrimsonR sparks electrical activity,” said Sahel. “It transforms the cells and makes them able to absorb light, though it takes a while – about four months – for the cells to take up the virus and the protein with it.”
Initial primate studies showed the method caused no adverse reactions. So, the team advanced to a human trial. For this, Sahel and his team worked with “a 58-year-old man who had been diagnosed with RP 40 years earlier and whose vision was limited to rudimentary light perception,” they reported, adding, “In a blind patient, we combined intraocular injection of an adeno-associated viral vector encoding ChrimsonR with light stimulation via engineered goggles. The goggles detect local changes in light intensity and project corresponding light pulses onto the retina in real time to activate optogenetically transduced retinal ganglion cells.”
ChrimsonR is not sufficient to restore function of the rods and cones. Instead, the protein makes shapes and shadows discernible at an amber color frequency. And the patient needs to wear a pair of goggles in order to regulate the intensity of the introduced light.
The team noted, “The patient perceived, located, counted and touched different objects using the vector-treated eye alone while wearing the goggles. During visual perception, multichannel electroencephalographic recordings revealed object-related activity above the visual cortex…This is the first reported case of partial functional recovery in a neurodegenerative disease after optogenetic therapy.”
Just a few months following the introduction of the technique, the test subject’s vision began to improve. Over time, he was able to “detect the crosswalk at an intersection and count the number of white stripes demarcating it; perceive objects like a plate, a mug and a phone; spot a piece of furniture in a room and see a door in a corridor. He can also detect where people are,” said Sahel. “We think this could last at least ten years or it could be for a lifetime. If not, we can always go back and re-inject.”
Further research must be done in order to fine-tune the methods used. However, the results suggest that, eventually, this may be a permanent solution to reversing RP.