Millions of people all over the world suffer from partial blindness – caused by glaucoma, a stroke or traumatic brain injury. For years, the loss of vision was deemed irreversible. But now a new treatment makes it possible to improve eyesight and vision.
At MEDICA.de, Prof. Bernhard Sabel explains the connection between electrical stimulation and vision and their impact on people affected by partial blindness.
Professor Sabel, before we address the subject of "being unable to see", we first need to know how "normal vision" works. Could you briefly explain this?
Prof. Bernhard Sabel: Vision begins with the eye where light is transduced by the retina into neural impulses. The optic nerve then carries the impulses to the brain. The brain interprets and analyzes these impulses. The eye is a "microphone" as it were, while the brain is the "amplifier". This means the brain plays a key role in vision. There are many diseases that can affect this nervous system and that cannot be improved by prescribing glasses as is the case in problems with the lens.
What happens in the case of partial vision loss caused by glaucoma for example?
Sabel: Injury resulting in loss of vision is caused by nerve cells being damaged or destroyed. This might occur at various locations along the visual system, in the retina, in or at the nerve or in the brain. The primary trigger is cells not being sufficiently supplied with blood or oxygen. That’s because the blood vessels are no longer able to supply enough blood to the cells due to high pressure in the eye, as is the case with glaucoma. But there are also acute diseases that are not directly caused by insufficient blood flow. In the case of an accident, for example, a bone might press against the optic nerve, causing a partial transection. Ultimately, the cause is inactivation or even the death of cells that process the visual information in the brain, nerve and in the retina.
You developed a treatment that improves eyesight and vision in glaucoma patients, among others. How does this work?
Sabel: The goal of the treatment is to strengthen the remaining vision. You can visualize this like a lawn. If you rake a lawn, you destroy a lot of grass but some of it survives. The nervous system works the same way. Damage to the nervous system might mean that there are areas where all the cells have died off. And there are other areas that remained completely intact. And there are yet other areas where some cells survived even though others have died off. Typically, these few remaining cells are not enough to drive normal functions since they are being "ignored" by the brain. That is to say, the brain focuses on the intact regions and neglects the partially damaged areas. By using stimulation, we generate more activity in the partially damaged tissue regions.Basic research has taught us that those areas of the brain we regularly use are being strengthened. This same principle is behind electrical stimulation. The alternating current stimulates cells to become active to where they are being supplied with more blood. The electrical stimulation also results in cells being prompted to send impulses again. If they do this often enough, the cells in the partially damaged areas are subsequently strengthened in their function. This gives them an advantage over the "competing" healthy tissue, which in turn improves vision. This is not a regeneration but rather an activation of cells that wake up from their "hibernation" so to speak
How did you come up with the idea of using electrical impulses to improve vision?
Sabel: Around 1900, Dr. Mann made a similar observation. He reported that it might help patients to improve their eyesight if electrical current stimulates the brain. But this knowledge was forgotten. Much later, around the year 2000, it became popular in neuroscience to use direct current to stimulate the brain. That said, this "neuromodulation" process was first researched in other areas unrelated to vision. Eventually, we used this technique for these treatment purposes.
We already observed in the past that it is possible to improve eyesight through vision training, for instance with simple exercises on the computer. The conclusion was that eyesight works even better with electrical stimulation. After all, it generates far greater cell activation than simple exercises on a monitor are capable of doing. We subsequently conducted several clinical trials and have treated hundreds of patients by now. We have achieved excellent results with this.
"Brain plasticity" also plays an essential role in your treatment. What is that?
Sabel: The brain is able to adapt and improve, for instance through training. This capability of the brain is called "plasticity". The brain does a wonderful job in extracting and strengthening information even if this information is very sparse. This knowledge is also vitally important for ophthalmology.
What types of opportunities do you see in the future to combine electrical stimulation with ophthalmology?
Sabel: I believe that electrical stimulation will essentially become a new treatment option for ophthalmology. The brain does not care why there are fewer signals coming in. Instead, it strengthens those that do arrive. This is why electrical stimulation is well suited as a kind of universal process for different types of diseases in ophthalmology; at least for those people who still have some remaining vision. Today the field of neurology fiercely researches how electrical stimulation therapy can improve functions to where various types of applications are already available, such as the improvement of motor function in patients with apraxia and movement disorders for example. There are already a number of studies worldwide on the use of non-invasive brain stimulation. In neurology, and especially in the area of neurological rehabilitation, these new approaches are widely accepted. Having said that, this knowledge has not fully made its way into ophthalmology yet.