Modern OCT devices can see inside the eye without a scalpel, but they don’t always capture everything that’s important. Some important information is simply lost and blurred by scattered photons. STOC-T technology, developed over many years by Professor Maciej Wojtkowski and his team at ICTER, aims to solve this problem by fundamentally changing the way image data is collected, rather than post-processing.
Optical coherence tomography (OCT) has become one of the cornerstones of modern ophthalmology. The patient sits in front of the device, focuses on the target, and immediately the doctor can see a detailed cross-section of the retina, layer by layer, without any physical contact with the eye. This is one of the most important advances in ophthalmology in the past 30 years. OCT allows clinicians to detect glaucoma, age-related macular degeneration, diabetic retinopathy, and macular edema before patients experience significant vision loss.
However, there is complex physics behind this seemingly simple test. The light that enters the eye does not return to the detector in perfect order. Some photons carry useful information about the tissue being examined. Other signals are scattered, reflected in random directions, and mixed with the desired signal. The result is reduced image contrast, increased graininess, and reduced clarity. Ironically, these obscure details often hide early signs of illness. Professor Maciej Wojtkowski, director of the International Center for Translational Eye Research (ICTER) at the Institute of Physical Chemistry at the Polish Academy of Sciences in Warsaw, has been working on this challenge for many years. In the article:Spatiotemporal optical coherence imaging and tomography for in vivo applications” was published. Biomedical Optics JournalWe now discuss STOC technology and its three-dimensional implementation, STOC-T. This method is designed not only to improve image quality but, more importantly, to separate true tissue signal from noise already at the data acquisition stage.
Why are eye images sometimes incomplete?
The retina is thin, complex, and delicate, but the choroid (the vascular layer directly beneath it) is even more difficult to visualize at full resolution. Photoreceptors, the cells directly involved in vision, are only a few micrometers in size. All these properties of the eye’s components make imaging extremely difficult, especially considering the properties of the stimulating light.
If a photon originating from a single point within the eye tissue hits multiple detection pixels instead of the correct pixel, the resulting image will not be a faithful representation of the structure being examined. Professor Wojcikowski calls this phenomenon “optical crosstalk” (OC). For physicists, OC is a problem of interference and loss of coherence. For physicians, OC results in a loss of diagnostic information. For patients, OC may increase the risk of early pathological changes remaining undetected.
“The goal in imaging biological tissue is not just to collect as much light as possible. We also need to know which light tells us something meaningful about the tissue and which light simply degrades the image.” says Professor Maciej Wojtkowski.
How does STOC-T improve images?
STOC-T is not another image processing filter applied after signal acquisition. Instead, the way data is collected changes. The system uses different spatial patterns known as phase masks to repeatedly change the phase of light that illuminates the tissue. The recorded signals are then compared and averaged. The scattered light behaves chaotically and differently for each mask, gradually canceling out its contribution to the image. In contrast, light carrying reliable structural information remains stable and becomes increasingly dominant after averaging.
A useful analogy is trying to hear a particular conversation in a crowded, noisy room. If the background noise is random but the desired audio is consistent, a well-designed recording system can isolate the noise. Similarly, STOC-T uses light instead of sound to focus on the desired signal in real time.
“We don’t treat noise as something to be fixed visually after the fact. Instead, we strive to design the measurement process so that interfering signals never have a chance to contaminate the image in the first place.” Professor Maciej Wojtkowski added:
In highly scattered tissues, some of the information may be lost at the moment of acquisition. Therefore, no post-acquisition algorithm can completely reconstruct an accurate image from an already distorted image. STOC-T resolves issues early, before the image is built.
What did the team demonstrate?
This publication describes results obtained in both laboratory models and living biological tissues. In one experiment, Professor Wojcikowski’s team imaged a standard-resolution target that was first covered with a strongly scattering artificial layer and then with a 100-micrometer-thick layer of rat skin representing natural tissue. Without STOC-T, the images were highly distorted in both cases. After applying phase modulation, the target structure became clearly visible again. This experiment illustrates the scale of the challenge. The object was always present, but without STOC-T, information about it was effectively lost on the way to the detector.
However, the most important results come from applying this technique to retinal imaging. STOC-T can visualize the ultrastructure of retinal layers, photoreceptors, ganglion cells, and the choroid with a lateral resolution of approximately 5 micrometers, close to the scale of individual cells.
Additionally, STOC-T facilitates optical retinography (ORG), which records photoreceptor responses to light. While it is useful to know what these light-sensing cells look like, knowing whether they function properly is often a more clinically important question. This journal article describes the measurement of cone photoreceptor responses to flickering light at frequencies between 1.5 and 45 Hz. The derived time constants were approximately 398 ms and 43 ms. These values are in good agreement with measurements of photoreceptor activity obtained using patch-clamp recordings in the primate retina, suggesting that STOC-T-based ORGs may indeed reflect local cone responses. Such information is particularly valuable in diseases where cellular function begins to decline before structural changes become visible. In these cases, the eye may still look normal, even though the cells are already behaving differently.
Who will benefit from improved imaging?
According to the World Health Organization, at least 2.2 billion people around the world live with visual impairment. In more than 1 billion cases, vision loss could have been prevented or treated if diagnosed early and accurately. In glaucoma, it is difficult to restore lost nerve fibers. Diabetic retinopathy can lead to serious complications if vascular changes are detected too late. In macular diseases, rapid diagnosis and accurate treatment monitoring can determine whether a patient retains central vision.
STOC-T is not yet a clinical product. This report clearly outlines the current limitations. This method requires a high-speed CMOS camera (512 x 512 pixels, operating at 60,000 frames per second) and a tunable laser that covers the wavelength range from 800 to 870 nm. And it generates huge amounts of data. A single retrieval can exceed 8.5 GB, creating a significant computational challenge.
The researchers also believe there is great potential in using multimode optical fibers as an alternative phase modulation mechanism. For example, a fiber with a core diameter of 50 μm and a length of 300 m can support approximately 800 propagation modes. In theory, this could reduce optical crosstalk noise by almost 29 times without the need for active control electronics.
“This is not the end of the journey. We already know what needs to be improved: speed, data volume, phase encoding, automation of reconstruction, etc. But the underlying concepts and ways of explaining the phenomena offer tremendous opportunities both for the development of new imaging devices and for further innovation of the method itself.” Professor Maciej Wojtkowski concludes:
sauce:
Institute of Physical Chemistry, Polish Academy of Sciences
Reference magazines:
Wojtkowski, M., (2026) Spatiotemporal optical coherence imaging and tomography. alive application. Journal of Biomedical Optics. DOI: 10.1117/1.JBO.31.11.113504. https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-31/issue-11/113504/Spatio-temporal-optical-coherence-imaging-and-tomography-for-in-vivo/10.1117/1.JBO.31.11.113504.full
