New therapy allows blind people to detect simple objects

Finding a doorway, following a line or detecting an object on a table: For people who are nearly or completely blind due to advanced retinitis pigmentosa, such tasks can become impossible. Retinitis pigmentosa is a group of inherited retinal diseases in which the light-sensing cells of the retina gradually degenerate.

An international research team has tested a therapy in a group of ten patients. The study was led by Professor José-Alain Sahel from the University of Pittsburgh and Professor Botond Roska from IOB and the University of Basel. GenSight Biologics and other international research partners were also involved.

In 2021, the same research team reported that a single blind patient was able to perceive objects again using the approach. The new study, published in the New England Journal of Medicine, now shows that similar improvements can also be observed in other patients.

New light sensors for the retina

The approach combines gene therapy with special goggles. The gene therapy modifies certain nerve cells in the retina that remain intact despite the disease. Normally, these so-called retinal ganglion cells are not sensitive to light themselves. Instead, they transmit signals from the retina’s light-sensing cells to the optic nerve.

The gene therapy provides the ganglion cells with the genetic instructions for a light-sensitive protein. This enables the cells to respond to light themselves. This approach is known as optogenetics - a method for which three researchers were recently awarded the 2026 Nobel Prize in Medicine.

The accompanying goggles use a camera to capture the surroundings and convert changes in the visual scene into light signals that activate the modified ganglion cells.

The primary aim of the study was to assess the safety of the treatment. The researchers also investigated whether there were signs of improved visual function.

Overall, the treatment was well tolerated. Most eye-related adverse events were mild or moderate. A temporary blockage of blood flow in the retina immediately after the injection was classified as severe. It resolved completely within minutes after treatment.

With the special goggles, the treated eye became more sensitive to light in seven of the ten participants following gene therapy. In six of them, the improvement reached the predefined threshold for a clinically meaningful change.

Eight participants also completed a range of tests in which they had to detect objects or determine their location, for example. Four showed consistent improvements across several of these tests. However, the results varied considerably between individuals. 

One advantage of the new treatment is that it does not target a specific genetic defect. Changes in more than 100 different genes can cause retinitis pigmentosa. Treatments that address the genetic cause directly therefore need to be tailored to the particular form of the disease. Optogenetic therapy sidesteps this problem by turning surviving ganglion cells into new light sensors.

The brain has to learn to use the new signals

The treatment alone is not enough. Patients have to learn how to use the unfamiliar visual signals. In the study, participants who had more training with the goggles tended to perform better in the tests. Training could therefore become an important part of this type of therapy.