And now, a research team at the University of Southern California (USC) is developing a new treatment model that can stimulate retinal neurons with ultrasound waves.
With the increasing rate of elderly people around the world, a 'silver tsunami' is expected by experts, and in relation to this, it is not surprising that the number of people with visual impairment is also anticipated to surge.
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Many of the cases are expected to have retinal degenerative diseases, the progressive degeneration of the light-sensitive receptors in the retina. There isn't a non-invasive treatment for the disorder yet, therefore, new technologies that can restore vision loss are still needed.
The current treatment employed by ophthalmologists is an invasive surgery that requires the implantation of electrode devices inside the eye. So this new approach may be the non-surgical solution we need for easier treatment of vision loss.
"Right now, we are doing animal studies trying to use ultrasound stimulation to replace electric stimulation," said Qifa Zhou, a professor of biomedical engineering and ophthalmology at USC. He is also Zhou leads the study along with Mark S. Humayun, one of the inventors of Argus II, the world's first artificial retina.
Stimulating the retina
The treatment will be provided by a wearable ultrasound device that will stimulate the retina by applying mechanical pressures to the eye. So that neurons will be activated and will send signals to the brain.
"The neurons present in the retina of the eye possess mechanically sensitive channels that respond to mechanical stimulation," said Gengxi Lu, who is a Ph.D. student in Zhou's lab. "These neurons are activated when we use ultrasound to generate mechanical pressure."
For the testing process of the approach, the researchers used a blind rat and used high-frequency ultrasound waves to stimulate its eyes. They projected patterns on a specific region of the eye, but since the rat is unable to inform the scientists about what it was seeing, the team measured the activity of the visual cortex of the rat via an electrode array. In the end, it turned out that the rat perceived visualizations that were projected to the eye.
The next step is testing the method on non-human primates and then adapting the ultrasound waves to a wearable contact lens. "Right now, we are using a transducer placed in front of the rat's eyeball to send the ultrasound signals to the retina, but our final goal is to create a wireless lens transducer" stated Dr. Zhou.
The study was published in the journal BME Fronters.
Objective. Retinal degeneration involving progressive deterioration and loss of function of photoreceptors is a major cause of permanent vision loss worldwide. Strategies to treat these incurable conditions incorporate retinal prostheses via electrically stimulating surviving retinal neurons with implanted devices 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 on the retina can evoke neuron activities from the visual centers including the superior colliculus and the primary visual cortex (V1), in either normal-sighted or retinal degenerated blind rats in vivo. The neuron activities induced by the customized spherically focused 3.1 MHz ultrasound transducer have shown both good spatial resolution of 250 μm and temporal resolution of 5 Hz in the rat visual centers. An additional customized 4.4 MHz helical transducer was further implemented to generate a static stimulation pattern of letter forms. Conclusion. Our findings demonstrate that ultrasound stimulation of the retina in vivo is a safe and effective approach with high spatiotemporal resolution, indicating a promising future of ultrasound stimulation as a novel and noninvasive visual prosthesis for translational applications in blind patients.