The use of ultrasound in medical technology is gaining more and more momentum every day. They have just been reported to be used to treat patients with type 2 diabetes and waking coma.
And now, a research team from the University of Southern California (USC) is developing a new treatment model that can stimulate retinal neurons with ultrasound waves.
With the increase in the number of older people around the world, experts are expecting a “silver tsunami” and, in relation to this, it is not surprising that the number of visually impaired people is also expected to increase.
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Many cases are expected to suffer from retinal degenerative diseases, the progressive degeneration of photosensitive receptors in the retina. There is not yet a non-invasive treatment for the disorder, therefore new technologies capable of restoring vision loss are still needed.
The current treatment employed by ophthalmologists is invasive surgery that requires the implantation of electrode devices inside the eye. This new approach could therefore be the non-surgical solution we need to facilitate the treatment of vision loss.
“Right now, we’re doing animal studies trying to use ultrasound stimulation to replace electrical stimulation,” said Qifa Zhou, professor of biomedical engineering and ophthalmology at USC. He is also Zhou leading the study with Mark S. Humayun, one of the inventors of Argus II, the world’s first artificial retina.
Stimulate the retina
The treatment will be provided by a portable ultrasound device which will stimulate the retina by applying mechanical pressure to the eye. While the neurons will be activated and send signals to the brain.
“Neurons in the retina of the eye have mechanically responsive channels that respond to mechanical stimulation,” said Ph.D. Gengxi Lu. studying in Zhou’s lab. “These neurons are activated when we use ultrasound to generate mechanical pressure.”
For the process of testing the approach, the researchers used a blind rat and used high-frequency ultrasonic waves to stimulate its eyes. They projected patterns onto a specific region of the eye, but because the rat is unable to tell scientists what it was seeing, the team measured the activity of the rat’s visual cortex via an array of electrodes. In the end, it turned out that the rat perceived visualizations that were projected to the eye.
The next step is to test the method on non-human primates and then adapt the ultrasound waves to a wearable contact lens. “At the moment, we’re using a transducer placed in front of the rat’s eyeball to send the ultrasound signals to the retina, but our end goal is to create a wireless lens transducer,” Dr. Zhou said.
The study was published in the journal BME borders.
Goal. Retinal degeneration involving progressive deterioration and loss of function of photoreceptors is a leading cause of permanent vision loss worldwide. Strategies to treat these incurable conditions include retinal prosthetics via electrical stimulation of surviving retinal neurons with devices implanted in the eye, optogenetic therapy, and sonogenetic therapy. Existing challenges of these strategies include invasive manner, complex implantation surgeries and risky gene therapy. Methods and results. Here, we show that direct ultrasound stimulation to the retina can evoke neural activities of visual centers, including the superior colliculus and primary visual cortex (V1), in blind normal-vision or retinal degenerate rats in vivo. Neural activities induced by the custom 3.1 MHz spherically-focused ultrasound transducer showed both good spatial resolution of 250 μm and temporal resolution of 5 Hz in rat visual centers. An additional custom 4.4 MHz helical transducer was then implemented to generate a static stimulation pattern of the letterforms. Conclusion. Our results demonstrate that ultrasound stimulation of the retina in vivo is a safe and effective approach with high spatio-temporal resolution, indicating a promising future of ultrasound stimulation as a novel and noninvasive visual prosthesis for translational applications in blind patients.