Using Ultrasound to Restore Vision: How Sound Waves Could Help the Eye

Ultrasound is sound at frequencies far above what the human ear can hear. People normally hear between 20 hertz and 20 kilohertz, but ultrasound is measured in kilohertz (kHz) or megahertz (MHz) and stays inaudible no matter how intense it is. Because it has a very short wavelength, it can pass through body tissues. It travels as a mechanical wave, moving faster through stiff tissue like bone and slower through soft tissue like fat. This is the same property that lets doctors create ultrasound images of an unborn baby, and unlike X-rays, ultrasound does not have the ionising effects that can damage DNA.

Researchers have found that ultrasound can also influence nerve cells. Low-intensity, low-frequency ultrasound has been shown to change brain activity in mice, and other studies showed that ultrasound applied to the retina can switch on the retinal ganglion cells that carry visual signals to the brain. This has led to growing interest in using ultrasound to help restore sight, especially through a technique called sonogenetics.

In sonogenetics, genetic engineering is first used to add a gene that makes a special protein in a nerve cell's membrane. This protein responds to mechanical pressure, so the treated nerve cells can then be switched on, in a controlled way, using ultrasound waves. The eye is well suited to this approach because its parts, including the lens, cornea, retina and the fluid inside, are easy to reach with ultrasound. The aim is to help in conditions where the optic nerve is damaged, such as glaucoma or after infections that affect the brain, where stimulating the visual cortex can bring back some vision.

Most of this work has been done on animals, but human use has begun. In 2025, a team at a medical university in China used ultrasound on 16 glaucoma patients with reported success. A separate device has been developed that focuses ultrasound on a part of the eye called the ciliary body to lower the pressure inside the eye, which is the main problem in glaucoma. High-intensity focused ultrasound also has other medical uses, such as heating and destroying cancer cells precisely while sparing nearby healthy tissue. Such devices still need approval from the relevant national health regulators before wide use.

For exams, this topic fits science and technology current affairs and basic physics of sound. It is useful for understanding the difference between sound and ultrasound, why ultrasound is safer than X-rays, and how new techniques like sonogenetics combine genetics and physics for medical treatment.