Using ultrasound to restore vision

A normal human hears sound in the frequency range 20 hertz (Hz) to 20 kilohertz, and the normal loudness, measured in decibels (dB), is between 30 and 70 db. Higher volumes, e.g. 85 dB and above, can lead to hearing damage. Ultrasound is defined as sound frequencies far beyond the audible range, and are expressed in kilohertz (kHz) or megahertz (MHz).

Regardless of its intensity, ultrasound is inaudible to the human ear. Ultrasound’s very short wavelength allows it to travel through biological tissues. It is also propagated as a mechanical wave, where one molecule pushes against the next, and therefore it travels at a faster speed in stiff and incompressible tissues such as bone but is slower in tissues such as fat. This property is used to generate ultrasound ‘images’ of human foetuses. (Ultrasound is much safer than X-rays, whose ionising effects can damage DNA.)

At a low intensity, low frequency ultrasound (200-700 kHz) allows the modulation of neural activities in mouse brains. W.J. Tyler et al. of Arizona State University showed this in 2008. Similarly, M. Menz et al. pointed out in 2013 that neural stimulation in the retina of a test amphibian (salamander) occurred when ultrasound of 43 MHz was applied (Journal of Neuroscience, 33, 4550). At such a high frequency, constant pressure is applied on the surface of the retinal tissue, which results in the activation of the retinal ganglion cells that send signals to the brain.

This phenomenon recently sparked interest in the potential of ultrasound stimulation and sonogenetics to restore vision (Jie Ji et al.; Neural Regen. Res. 20: 3501). Sonogenetics makes use of the non-invasive nature of ultrasound to modulate the activity of small groups of neurons in living organisms. Genetic engineering is first used to deliver a gene that makes a mechanosensitive protein in a neuron’s cell membrane. The neurons can then be activated on demand by ultrasound waves.

The eye, in particular, is easily accessible to ultrasound and the lens, cornea, retina, and the vitreous humor are easily studied using ultrasound. Of particular interest are attempts to restore vision when the optic nerve is impaired. This happens in degenerative conditions such as glaucoma, and the ensuing optic neuropathy, and infectious diseases that affect the brain (e.g. meningitis). In these conditions, ultrasound stimulation of the visual cortex in the brain can lead to some restoration of vision (Chen Gong et al., Bioengineering 10:577, 2023).

High-intensity focused ultrasound waves have other therapeutic uses, too. For example, in cancer treatment, precision focusing on a tumour can cause the temperature in these cells to rise rapidly to 65-85 ºC, effectively killing these cells while leaving the surrounding tissue unharmed.

All these studies have used animals as models. Has anyone actually used sound waves to treat retinal disorder in human patients? The answer is yes. In 2025, Wang et al. from Chongqing Medical University in China did so with 16 glaucoma patients, using ultrasound, and with success. Further, an agency called Focused Ultrasound Foundation from Charlottesville, Virginia, in the U.S., has also developed a device called ‘Eye Tech Care’ that the Foundation has claimed can focus ultrasound on the ciliary body, decreasing the intraocular pressure and thus treating glaucoma. This technology, however, needs to be cleared by the U.S. National Health Agency.

The author thanks Dr. Srinivasu Karri of the Hormel Institute, Minnesota, USA, for access to several references.

dbala@lvpei.org