Rod-cone therapy is independent of the gene and focused on treating the rods in the eye while keeping the cones intact. With Usher Syndrome, the rods of the retina die first (see light and dark). Then the cones, which are more important for seeing because they enable us to read and to see colours, degenerate. The rods are important for night vision, but they can also produce proteins that are essential for survival of the cones. When a rod degenerates, the cones also degenerate after this.
Professor Sahel from Paris demonstrated in various animal models with rods-cones dystrophy such as retinitis pigmentosa that he could protect the cones by means of this therapy. Even the structure of the cones, the morphology, was improved. A clinical trial with a selective group of patients will start in 2020. Hopefully, this trial will prove that the degeneration of the cones can be prevented. Subsequently, this therapy is to be tested in a much larger group of patients, including patients suffering from Usher Syndrome and retinitis pigmentosa.
There are two types of photoreceptors: cones and rods. The cones work when there is light outside or when enough lamps are on. Then we see colours and the details straight ahead of us. Most cones are in the centre of the retina, the macula (yellow spot). Reading and recognising faces is the work of the macula. The rods are used to see in the dark and so observe things out of the corners of our eyes. However, we cannot see details and colours with rods. Therefore we cannot read or properly recognise faces in the dark and we see everything in shades of grey at night.