Confocal microscope image of rod (green) and cone (red) photoreceptors in a human retina.Dr. Robert Fariss, National Eye Institute, NIH, CC BY
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.