Summary: Focused ultrasound that stimulates the retina could offer a noninvasive path to restoring vision for people with blindness caused by photoreceptor degeneration.
Source: USC
The number of Americans living with visual impairment or blindness is projected to rise to more than 8 million by 2050, according to estimates from the USC Gayle and Edward Roski Eye Institute (2016).
As the youngest baby boomers reach age 65 by 2029, age-related eye disease is expected to increase dramatically during a so-called “silver tsunami.” A large portion of that burden will come from retinal degenerative diseases, in which the light-sensitive photoreceptors of the retina progressively deteriorate and die.
These projections highlight an urgent need for new, effective technologies to treat vision loss caused by photoreceptor degeneration. At present, there are few successful noninvasive therapies for restoring sight. The USC research team has developed a promising new approach that could fill this gap.
Today, restoring vision for many blind patients typically relies on electronic retinal prostheses that electrically stimulate surviving retinal neurons via implanted electrode arrays. While effective in some cases, these devices require complex and expensive eye surgery to implant hardware inside the body.
Researchers in the USC Viterbi School of Engineering’s Department of Biomedical Engineering are investigating a fundamentally different, non-surgical strategy that uses another sense to reactivate the visual system: sound.
Ultrasound technology
“This is an innovative technology,” said Qifa Zhou, professor of biomedical engineering and ophthalmology at USC. “We are currently conducting animal studies to determine whether ultrasound stimulation can effectively replace electrical stimulation.”
The team is led by Zhou and Mark S. Humayun, professor of ophthalmology and biomedical engineering and one of the inventors of the Argus II artificial retina. Their approach uses focused ultrasound waves to mechanically stimulate retinal neurons without implanting devices into the eye.
“A wearable ultrasound system would generate focused sound waves to stimulate the retina,” explained Gengxi Lu, a Ph.D. student in Zhou’s lab. “No invasive surgery and no implanted hardware would be required.”
The concept builds on a familiar observation: when you press gently on a closed eye, you can see flashes or shapes. Those sensations arise because mechanical pressure activates neurons in the retina and sends signals to the brain. In this work, the team uses ultrasonic pressure waves—inaudible high-frequency sound—to produce a similar mechanical activation of retinal neurons in blind eyes.
“Retinal neurons contain mechanically sensitive ion channels that respond to pressure,” Lu said. “Ultrasound generates localized mechanical forces that open these channels, triggering neural activity.”
How it works
To test the idea, the researchers used focused, high-frequency ultrasound to stimulate the retinas of blind rats in preclinical experiments. The ultrasound transducers they designed are comparable in concept to medical ultrasound probes used for fetal imaging, but they operate at higher frequencies and are tailored to target small regions of the eye.
By focusing the ultrasound beam on specific retinal locations, the team produced spatially patterned stimulation. For example, when ultrasound waves were projected in the shape of a letter “C,” electrophysiological recordings from the animals’ visual brain areas showed activity patterns consistent with that shape.
Because animals cannot describe their visual experience verbally, the researchers recorded electrical responses from the superior colliculus and primary visual cortex using multi-electrode arrays. These recordings demonstrated that the patterned ultrasound elicited spatially and temporally precise responses in visual centers of both sighted and retinal-degenerated rats.
The customized spherically focused 3.1 MHz transducer used in the study produced spatial resolution around 250 μm and temporal resolution up to 5 Hz in the rat visual centers. An additional 4.4 MHz helical transducer generated static stimulation patterns such as letter forms. These results were published in BME Frontiers.
The future
This work is supported by a four-year, $2.3 million grant from the National Eye Institute. The team has applied for additional NEI funding to advance the research toward translational studies. Current experiments use rodent models; the researchers plan to move to non-human primate studies before initiating human clinical trials.
“At present we place a transducer in front of the rat’s eye to deliver the ultrasonic stimulation,” Dr. Zhou said. “Our long-term goal is to develop a wireless, wearable lens-based transducer that can provide targeted, high-resolution retinal stimulation.”
Future work will focus on improving spatial and temporal resolution, refining stimulation patterns, and engineering a wearable ultrasound contact lens or headset suitable for human use. A patent application is pending for this ultrasound retinal stimulation technology, which could offer a safe, noninvasive visual prosthesis option for people with retinal degeneration.
About this visual neuroscience and neurotech research news
Author: Amy Blumenthal
Source: USC
Contact: Amy Blumenthal – USC
Image: The image is in the public domain
Original Research: Open access.
“Noninvasive Ultrasound Retinal Stimulation for Vision Restoration at High Spatiotemporal Resolution” by Qifa Zhou et al., published in BME Frontiers.
Abstract
Noninvasive Ultrasound Retinal Stimulation for Vision Restoration at High Spatiotemporal Resolution
Objective. Retinal degeneration, characterized by progressive loss of photoreceptors, is a leading cause of permanent vision loss worldwide. Current therapeutic strategies include implanted retinal prostheses that electrically stimulate surviving retinal neurons, optogenetic approaches, and gene-based sonogenetic techniques. These approaches face challenges such as invasiveness, complex surgeries, and gene therapy risks.
Methods and results. The study demonstrates that direct ultrasound stimulation of the retina evokes neuronal activity in visual centers—including the superior colliculus and primary visual cortex—in both normal and retinal-degenerated rats in vivo. A custom 3.1 MHz spherically focused transducer yielded spatial resolution of roughly 250 μm and temporal resolution of 5 Hz in the rat visual system. A 4.4 MHz helical transducer produced static letter-like stimulation patterns, and multi-electrode recordings confirmed corresponding activity in visual brain areas.
Conclusion. These findings indicate that focused ultrasound can safely and effectively stimulate the retina with high spatiotemporal precision in vivo, supporting the potential of ultrasound-based, noninvasive visual prostheses for translational application in patients with retinal degeneration.