An NTU Singapore-led team has, for the first time, captured a tiny mechanical twitch in the eye’s night-vision cells as they detect light. The breakthrough could pave the way for earlier, non-invasive detection of diseases that cause blindness.
A team led by Nanyang Technological University, Singapore, has captured a tiny mechanical movement in the eye at the exact moment it detects light — a discovery that could change how doctors spot blinding diseases long before vision is lost.
Using an advanced imaging technique, the international group recorded a rapid contraction in rod photoreceptors, the eye’s so-called night-vision cells, in both living human and rodent eyes. These cells allow us to see in dim light and are among the first to deteriorate in conditions such as age-related macular degeneration and retinitis pigmentosa.
Lead investigator Tong Ling, a Nanyang Assistant Professor in NTU’s School of Chemistry, Chemical Engineering and Biotechnology, described the newly observed motion as a kind of ignition point for sight.
“The ‘twitch’ of the eye’s night-vision cells is akin to the ignition spark of vision. We have long known that these cells produce electrical signals when they absorb light, but no one had, until now, ever reported the accompanying mechanical contraction of these cells inside the living eyes of humans or rodents,” he said in a news release.
Rod photoreceptors sit in the retina at the back of the eye and make up the vast majority of its light-sensing cells. They are incredibly sensitive, able to respond to very low levels of light, which makes them crucial for night vision but also vulnerable to early damage.
Ling noted that the work sheds light on a basic step in how the eye turns light into signals the brain can understand.
“The findings reveal a fundamental step in the process by which rod photoreceptors detect light and send visual information to the brain. These cells make up about 95% of all photoreceptors in the human retina,” he added.
The team’s findings were presented by Ling at the Association for Research in Vision and Ophthalmology 2024 Annual Meeting and published in the journal Light: Science & Applications.
To make the discovery, the researchers used a cutting-edge method called optoretinography, or ORG. Unlike traditional eye tests that rely on electrical recordings or require bright flashes and contact with the eye, ORG can detect extremely small movements in retinal cells without dyes, labels or touching the eye.
With ORG, the scientists measured a rapid contraction of rod cells of up to about 200 nanometers — roughly a thousandth the width of a human hair — within about 10 milliseconds of light hitting the retina. That is faster than a single flap of a hummingbird’s wings.
By combining these measurements with biophysical modeling, the team linked the motion to the activation of rhodopsin, the light-sensitive molecule inside rods. When rhodopsin absorbs light, it kicks off a cascade of events that ultimately produces the electrical signals sent along the optic nerve to the brain. The newly observed mechanical “twitch” appears to be one of the earliest physical signs of that process beginning.
Co-corresponding author Ramkumar Sabesan, an assistant research professor in the Department of Ophthalmology at the University of Washington School of Medicine, emphasized how powerful it could be to watch rods in action in real time.
“This is the first time we’ve been able to see this phenomenon in rod cells in a living eye. Rod dysfunction is one of the earliest signs of many retinal diseases, including AMD and retinitis pigmentosa. Being able to directly monitor the rods’ response to light gives us a powerful tool for disease detection and tracking treatment responses earlier and with greater sensitivity than any conventional diagnostic instrument,” he said in the news release.
Today, many clinical tools for assessing rod function are relatively blunt. They may require patients to sit through uncomfortable tests or can only pick up damage once it is fairly advanced. Because ORG is non-contact and non-invasive, it could make it easier to screen patients more frequently and to detect subtle changes in rod health before symptoms appear.
The new work builds on an earlier technique from the same research group, reported in 2024, that measured slower rod movements in response to dim visual stimuli. Together, these approaches offer a more complete picture of how rod cells behave over different timescales and light levels, potentially giving clinicians a richer set of signals to track disease.
Independent experts say the technology could be a game changer for both science and medicine. Jost Jonas, an ophthalmologist and clinical scientist who chairs the Department of Ophthalmology at Heidelberg University in Germany, called the approach both novel and promising.
“Optoretinography as brand-new technique is clinically and scientifically very interesting and promising, since it allows for the first time the non-invasive visualisation of movements of the cellular structures in a living person’s eye at the nanoscale. This holds true for the rods as photoreceptors as well as for other cells in the retina,” he said.
He added that the method “may thus open new avenues to better understand retinal cells in their working and in their relationship with neighbouring cells as well as may clinically allow a more detailed, and potentially earlier, diagnosis of retinal diseases, in particular of disorders primarily affecting the photoreceptors,” highlighting its potential reach beyond rod cells alone.
The project brought together biomedical engineers, physicists and clinical scientists from multiple institutions, including teams at the Singapore Eye Research Institute and Duke-NUS Medical School, who contributed expertise in retinal imaging and rodent models.
Looking ahead, the researchers envision ORG being refined and adapted for use in eye clinics. If future studies confirm that subtle changes in the rod “twitch” can reliably signal early disease, doctors could one day use a quick, painless scan to catch retinal disorders at a stage when treatments have the best chance of preserving sight.
For patients at risk of blindness, that could mean something simple but profound: keeping the spark of vision alive for many more years.