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REVITALIZATION OF PARTIAL VISION WITH OPTOGENETICS
16 July 2021
Retinitis Pigmentosa (RP) is a group of rare, genetic disorder that involves a breakdown and loss of cells in the retina. These cells are nothing but the light sensitive tissue that lines the back of the eye. It contain photoreceptors which are the cells present in the retina that begin the process of seeing by absorbing and converting the light into electrical signals which are further sent to other cells in the retina and ultimately through the optic nerve to the brain where they are processed into the images which we actually see. These are of types which include Rods present in the outer regions and Cones present in the central portion of the retina.
This inherited disorder results from harmful changes made in any of more than 50 genes which carry the information for making proteins that are needed for the photoreceptors. These mutations are so severe that the gene can't make the required protein, limiting the cells function. Few mutations even produce a toxic protein or even lead to a abnormal protein that doesn't function properly. In all these cases, the result is damage to the photoreceptors.
RP can be inherited in one of the three ways which includes firstly, Autosomal Recessive Inheritance where it take two copies of the mutant gene to give rise to the disorder. Secondly, Autosomal Dominant Inheritance where it takes just one copy of gene with a disorder-causing mutation to bring about the disorder. Thirdly, X-linked Inheritance where mother carry the mutation gene on one of their X-chromosome and pass it to their son as they have two x-chromosomes. Since mid 2000's, optogenetics, with it's potential to activate neurons with light, emerged as a promising technique for restoring vision in blind patient. The clinical trials to test optogenetics-based therapy in humans and one of them recently discovered that blind patient or nearly blind from RP could detect light and motion following treatment.
In regards this research, a 58-year old man who has already been diagnosed with Retinitis Pigmentosa, enrolled himself in the research. In order to compensate the loss of the photosensitive cells, the scientists has to make existing retinal ganglion cells which receive the information via other intermediate cells from photoreceptor respond to light. This is done by taking light sensors from microbes to the blind retina using gene therapy. Here, they have injected the gene for the artificial- channelrhodopsin Chrimsin R, into the central retina. The light sensing protein is delivered via adeno-associated viral vector, takes several months to be fully exposed on the surface of the cells.
Then it is activated with engineered goggles which detect light changes, correspond to peak sensitivity of the inserted protein onto the vector-treatment retinal cells. This coupling of injection and the goggles were not enough to restore vision, so the patient has been given visual training to control his eye movement. Before the treatment, the patient couldn't even able to detect anything but seven months after this training, he reported the first signals of visual improvement. Hence, this is a technique that enables rehabilitation. Now, the patient could able to perceive, locate and touch the objects in 92% of the trials which has been confirmed by EEG. The gain of sight in this patient is limiting which might be due to the low dose of viral vector but this research has given a huge hope for much more better results in the treatment of the patient suffering from RP and ultimately show them the light through the eyes of optogenetics.
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