An experimental optogenetic therapy improved light sensitivity in some people with advanced retinitis pigmentosa, an inherited group of diseases that progressively destroys the retina’s light-sensing cells. The early results are encouraging, but they fall well short of restoring normal sight.
The open-label study published in the New England Journal of Medicine enrolled 10 people who were legally blind and had little or no remaining vision. Seven participants became more sensitive to light after treatment, and six met the researchers’ threshold for a clinically meaningful improvement. That threshold, drawn from previous research rather than set before the trial, was a gain of at least 0.6 log units, or roughly four times greater light sensitivity.
How the treatment works
Retinitis pigmentosa can result from changes in more than 100 genes. Instead of correcting any one of them, the therapy targets retinal ganglion cells that can survive after photoreceptors have been lost.
Researchers injected the worse-seeing eye of each participant with an adeno-associated virus carrying instructions for ChrimsonR, a protein that responds to a particular wavelength of light. The goal was to turn the surviving ganglion cells into substitute light sensors. Participants then used special goggles with a camera and processor that translated the scene in front of them into light patterns capable of activating those modified cells.
The goggles produced a monochrome image, and the visual gains remained limited. According to the University of Pittsburgh School of Medicine’s account of the trial, some participants became better at detecting, locating or reaching for objects while wearing the goggles. Four showed consistent improvement across multiple practical tasks. Examples described in independent reporting by The Guardian included finding a notebook or doorway and following a line on the floor.
The treatment did not restore normal vision. Participants could not read or recognize faces, and the gains depended on using the goggles.
An early safety study
Safety was the study’s primary outcome. Researchers recorded 34 eye-related adverse events among nine participants: 23 were mild and 10 were moderate. One participant experienced a severe, temporary blockage of the central retinal artery after the injection. It resolved within minutes after treatment to lower pressure in the eye.
