Ultrasound Retinal prosthesis
Retinal diseases caused by progressive degeneration of photosensitive photoreceptors are one of the main causes of irreversible vision loss and blindness affecting tens of millions of people worldwide. Even when the photosensitive cells (rods and cones) of the retina completely degenerate, the nerve circuits going to the brain usually remain intact, and it is possible to partially restore vision by stimulating neurons. Strategies for treating degeneration include electrical stimulation of surviving retinal neurons using devices implanted in the eye and genetic therapy. The disadvantages of these methods are invasiveness, complex implantation operations and the risks accompanying gene therapy.
A research team led by Professors Kifa Zhou and Mark Humayun at the University of Southern California in Los Angeles subjected the eyes of both healthy rats and rats with retinal degeneration to stimulation with high-frequency sound waves. This sound is not perceived by the human ear, it can be manipulated and focused on the desired area of the eye. It is known that ultrasound can generate controlled mechanical pressure, and it activates neurons with the help of an unknown mechanism. Ultrasound stimulation led to the activation of small groups of neurons in the eyes of rats, just as light signals can activate retinal cells of a healthy eye.
The main limitation of the experiments conducted on animals is that, unlike humans, researchers could not get a reliable answer from them about visual sensations during ultrasound stimulation of the eye. The group solved this problem by measuring the activity of the visual region of the rat brain, to which the optic nerve is connected. With the help of a multielectrode matrix placed in this area, they recorded the activation of the retina. The study showed that when projecting ultrasound in the form of a pattern on the retina (for example, the letter "C"), it is possible to catch the corresponding activity in the brain.
One of the important requirements for an ultrasound prosthesis is to ensure the ability to see images as clearly as possible. To do this, the incoming data must contain many individual points. Are sound waves capable of transmitting small details to retinal neurons that do not merge with each other? The problem of resolving the experimental system has not yet been overcome. In rats, the ultrasound beam stimulated an area of the retina with a diameter of about 250 microns, while in the retina, individual neurons are only a few microns in size. Therefore, in order to achieve a better resolution, it is necessary to achieve a more subtle stimulation with ultrasound.
Experiments have shown that the neurons reacted most actively to ultrasound stimulation with a frequency of 5 Hz. But the human brain works at a much higher frequency, so with the new device, it can only see each image separately. Movie and video game makers know that images merge only at 24 frames per second. When the researchers performed ultrasound stimulation of the rat's retina at such a frequency, the neurons stopped functioning.
The authors believe that they can at least partially solve this problem. Experiments have shown that ten frames per second should be enough to successfully deliver signals to the brain.
If subsequent experiments are successful, the new technology can be translated into clinical trials within 3-5 years.
Article X.Qian et al. Noninvasive Ultrasound Retinal Stimulation for Vision Restoration at High Spatial Resolution is published in the journal BMEF (BME Frontiers).
Aminat Adzhieva, portal "Eternal Youth" http://vechnayamolodost.ru based on EurekAlert materials: Sound can stimulate blind retina to transmit signals to the brain – ultrasonic retinal prosthesis.