Gene Therapy to Add a New Photosensitive Protein to the Retina
Researchers have delivered a non-human photosensitive protein to the retina of a patient long blind from the loss of photoreceptor cells caused by retinitis pigmentosa. The outcome as described is not as good as the results produced by implantation of grids of electrodes into the retina, but that strategy has been under development for a somewhat longer number of years. This approach is in the very early stages: it is unclear as to how well one can engineer the retina to use alternative means of translating light into signals to the optic nerve, and how well the brain will adapt to such new sources of information over time. Still, the prospects for the blind are becoming more promising year after year, as the number of approaches to regeneration or replacement grows.
Optogenetics may enable mutation-independent, circuit-specific restoration of neuronal function in neurological diseases. Retinitis pigmentosa is a neurodegenerative eye disease where loss of photoreceptors can lead to complete blindness. In a blind patient, we combined intraocular injection of an adeno-associated viral vector encoding the channelrhodopsin 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.
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. The patient could not visually detect any objects before injection with or without the goggles or after injection without the goggles. This is the first reported case of partial functional recovery in a neurodegenerative disease after optogenetic therapy.