Science & Technology (Commonwealth Union) – For the first time, scientific researchers have noticed a minute mechanical movement in living human and rodent eyes precisely when a rod photoreceptor senses light. The international study was led by Nanyang Technological University, Singapore (NTU Singapore).
According to the researchers, this discovery opens the door to a new, non-invasive method for evaluating retinal health and could allow blinding eye diseases to be detected at an earlier stage. The collaborative project involved researchers from several institutions, including the University of Washington (UW), the Singapore Eye Research Institute (SERI), and Duke-NUS Medical School.
Rod photoreceptors are specialised retinal cells responsible for vision in dim light. Often described as the eye’s “night-vision cells,” they are highly sensitive and are usually among the first cells to be damaged in conditions such as age-related macular degeneration. Current techniques for examining rod function, however, lack sufficient sensitivity and can cause discomfort for patients.
Lead researcher Dr Tong Ling, a Nanyang Assistant Professor at NTU’s School of Chemistry, Chemical Engineering and Biotechnology, indicated that the tiny ‘twitch’ they observed in these night-vision cells is comparable to the spark that triggers vision and while it has long been established that rods generate electrical signals when they absorb light, this is the first time their associated mechanical contraction has been detected inside the living eyes of humans or rodents.
Dr Ling, who is also affiliated with NTU’s School of Electrical & Electronic Engineering, added that the findings uncover a crucial step in how rod photoreceptors sense light and relay visual information to the brain. He indicated that these cells account for roughly 95 per cent of all photoreceptors in the human retina.
The results were initially unveiled by Dr Ling at the 2024 Annual Meeting of the Association for Research in Vision and Ophthalmology and were published in full yesterday in the peer-reviewed journal Light: Science & Applications.
A new frontier in non-invasive eye imaging
Using a cutting-edge imaging technique known as optoretinography (ORG), which measures minute cellular movements in the eye without the need for dyes or labels, the researchers observed that rod photoreceptors rapidly contract by as much as 200 nanometres within about 10 milliseconds of light striking the retina — a response faster than a single beat of a hummingbird’s wings.
By integrating these observations with biophysical models, the team determined that the movement is triggered when rhodopsin, the eye’s light-sensitive pigment, is activated. This reaction represents one of the earliest stages in the process by which light is transformed into electrical signals that the brain recognises as vision.
Co-corresponding author Professor Ramkumar Sabesan, a vision scientist at the University of Washington School of Medicine, indicated that this marks the first time this effect has been observed in rod cells within a living eye. He further pointed out that impairment of rod function is among the earliest indicators of many retinal disorders, including age-related macular degeneration and retinitis pigmentosa and the ability to directly measure how rods respond to light offers a highly sensitive, non-invasive way to detect disease and monitor treatment effectiveness far earlier than existing diagnostic tools.
Rod photoreceptors are typically among the earliest cells to degenerate in blinding eye diseases. Combined with a technique developed by the same research team and reported in Nature Communications in 2024—which tracks the comparatively slow responses of rod photoreceptors to low-light stimuli—the newly described method offers clinicians a non-contact, non-invasive way to identify and monitor rod function.
Professor Jost Jonas, an ophthalmologist, clinical scientist and Chairman of the Department of Ophthalmology, Heidelberg University, Germany, speaking independently says “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.”
