Researchers at the University of Washington have modified the standard process of OCT (optical coherence tomography) to detect minute changes in response to light in individual photoreceptors in the living eye. The technique has potential in the testing of therapies such as stem cells or gene therapy to treat retinal disease.
“Typically, retinal OCT systems are implemented by raster scanning a point of light across the retina. This provides excellent contrast, but at the cost of speed due to dual-axis scanning,” corresponding author Ramkumar Sabesan, assistant research professor of ophthalmology, told Photonics Media. “On the other end, full-field OCT systems exist that can operate at higher speeds, but have lower resolution and contrast. A line-scan OCT sits in the middle, and allows an excellent opportunity to optimize speed, sensitivity, and resolution for high-resolution retinal imaging.”
The researchers built a high-speed line-scan spectral OCT with adaptive optics. In a line-scan OCT, a linear broad spectral band illumination is shined on the retina, and the backscattered light is captured after diffraction on a 2D sensor. By virtue of parallel acquisition of an entire retinal cross-section (B-scan) in a single high-speed camera frame, Sabesan said, depth-resolved tomograms at speeds up to 16 kHz were achievable in this study. Implementing phase-resolved OCT acquisition allows monitoring of nanometer-scale optical changes in response to light.
“The high speed allows tracking fast retinal events corresponding to light-evoked electrical activity in photoreceptors, by overcoming the ever-present eye motion in a living human,” Sabesan said. “Adaptive optics allows correcting the eye’s native aberrations and visualizing these minute nanometer-millisecond-scale physiological events in individual cells.”
Because photoreceptors are the primary cells affected in retinal generation and the target of many treatments, noninvasive high-resolution visualization of their physiology is invaluable, the researchers said in their paper.
“We hope the technology will serve as an early, safe, and highly sensitive retinal biomarker and serve two purposes in the clinic,” Sabesan told Photonics Media. “First it will help understand the mechanisms and time-course of dysfunction in disease and response to existing therapies. Second, it will help evaluate the safety and efficacy of new therapies on the horizon.”
The research was published in Science Advances (www.doi.org/10.1126/sciadv.abc1124).