A novel microscopy technique that expands on existing principles of adaptive optics — first developed to capture images of the sky without distortions from Earth’s atmosphere — has enabled University of Rochester researchers to track, in real time, the interactions of immune cells in a living eye without damaging the cells or surrounding tissue. The method is part of an imaging system that incorporates AI and infrared videography to noninvasively image and track translucent immune cells in live retinal tissue. The technique avoids the need to label individual immune cells with fluorescent agents, as well as the potential need to reinject the cells — a procedure that, while sometimes necessary for imaging purposes, may influence the behavior of the ocular cells. Where adaptive optics technology provides a way to correct for aberrations of the eye, allowing researchers and medical personnel to visualize individual cells located at the back of the eye, it fails to precisely inform on cellular behaviors. Optical coherence tomography (OCT) measures the thickness of retinal tissue, and, while that determination can serve as an accurate marker for the extent to which tissue may be inflamed, OCT too is unable to evaluate the behavior of tissue. However, by integrating a phase contrast technique into adaptive optics to capture images of translucent objects such as immune cells, University of Rochester vision scientist Jesse Schallek and his lab at the University of Rochester Center for Visual Science and Flaum Eye Institute reliably captured what cells are doing. By using time-lapse videography to capture images of immune-cell activity over periods of time ranging from milliseconds to months, the system allows Schallek to examine the cells at any speed over any timespan. Because multiple types of immune cells live in the eye, the team has additionally developed and deployed AI computer code to perform cellular differentiation. Ultrahigh-speed imaging of individual red blood cells allowed the team to simultaneously track blood flow and gauge how it changes in response to inflammation. Immune cells can cause the type of inflammation that is characteristic of most retinal diseases that lead to blindness, Schallek said. The cells mobilize to the site of affected tissue in the eye. Once there, they release compounds that bring additional immune cells to the location. “A defining characteristic of immune cells is that they are truly mobile and incredibly dynamic, rushing to wherever inflammation occurs,” said ophthalmologist Colin Chu, a visiting senior research fellow from the University of Bristol who worked in Schallek’s lab. “The first time we successfully imaged them was astounding, as we were essentially spying on them as they worked within their actual native setting.” Chu was part of the team that led the research study producing the technology with Aby Joseph, a Ph.D. candidate at the Institute of Optics at the University of Rochester. Microscopic immune cells escape a nearby blood vessel in response to inflammation. The color overlay shows computer detection of single cells that are tracked over time. Courtesy of Schallek lab. Beyond immune cells traveling to affected tissue and releasing compounds, changes in blood flow can also interfere with vision and complicate the progression of certain diseases. The high-speed imaging process indicated that veins and arteries achieve an increase in blood flow to the inflamed retina in different ways, Joseph said. The revelation could prove vital to theorizing, designing, and testing future treatments aimed at resolving inflammation. The new technology may hold forthcoming pharmaceutical applications, Schallek said. “Companies will now have way to look at how well specific drugs target specific components within the immune system. They will be able to see if they can improve the efficacy of drugs that are already approved, and others that are still in development.” The work was supported with funding from the National Eye Institute of the National Institutes of Health (NIH); Research to Prevent Blindness; F. Hoffmann-La Roche Ltd. Roche Academy of Distinguished Scholars; the Dana Foundation; and the World Universities Network WUN Research Mobility Programme award. The research was published in eLIFE (www.doi.org/10.1101/2020.07.07.191890).