High-Speed Laser System Takes Crisp, 3-D Retinal Images

In work that could improve diagnoses of many eye diseases, a new type of laser has been developed for taking high-resolution, 3-D images of the retina, the part of the eye that converts light to electrical signals that travel to the brain.

The research by Massachusetts Institute of Technology scientists will be presented at the Conference on Lasers and Electro-Optics and the Quantum Electronics and Laser Science Conference (CLEO/QELS) taking place in Baltimore May 6–11.

Professor James Fujimoto with a high-resolution, 3-D image generated using a new type of laser in combination with the optical coherence tomography (OCT) system he developed in the early 1990s with Eric Swanson of MIT Lincoln Laboratory. (Photo: John Cook, RLE)

The new imaging system is based on optical coherence tomography (OCT), which uses light to obtain high-resolution, cross-sectional images of the eye to visualize subtle changes that occur in retinal disease. OCT was developed in the early 1990s by MIT professor James Fujimoto, Eric Swanson at MIT Lincoln Laboratory and collaborators; Fujimoto is an author of the report to be presented next week.

"Within the last few years optical coherence tomography has become a standard diagnostic for ophthalmology. New techniques are now enabling dramatic increases in image acquisition speeds. These advances promise to enable new and powerful three-dimensional visualization methods which could improve early diagnosis of disease and treatment monitoring," said Fujimoto, who holds appointments in MIT's Department of Electrical Engineering and Computer Science and the Research Laboratory of Electronics.

Conventional OCT imaging typically yields a series of two-dimensional cross-sectional images of the retina, which can be combined to form a 3-D image of its volume. The system works by scanning light back and forth across the eye, measuring the echo time delay of reflected light along micrometer-scale lines that, row by row, build up high-resolution images.

Commercial OCT systems scan the eye at rates ranging from several hundred to several thousand lines per second. But a typical patient can only keep the eye still for about one second, limiting the amount of 3-D data that can be acquired.

3-D cut-away view of a human retina in vivo obtained with the new high-speed scanning technique.

Now, using the new laser, researchers in Fujimoto's group report retinal scans at record speeds of up to 236,000 lines per second, a factor of 10 improvement over current OCT technology. Future clinical studies, as well as further development, may someday enable ophthalmologists to routinely obtain 3-D "OCT snapshots" of the eye, containing comprehensive volumetric information about the microstructure of the retina. Such snapshots could potentially improve diagnoses of retinal diseases such as diabetic retinopathy, glaucoma and age-related macular degeneration.

Fujimoto's colleagues on the work are Robert Huber, a visiting scientist at MIT now at the Ludwig-Maximilians University in Germany, Desmond C. Adler and Vivek Srinivasan. Adler and Srinivasan are both graduate students in EECS.

The current research was sponsored by the National Science Foundation, the National Institutes of Health and the Air Force Office of Scientific Research.

The paper, "Fourier Domain Mode Locking (FDML) in the Non-Zero Dispersion Regime: A Laser for Ultrahigh-Speed Retinal OCT Imaging at 236kHz Line Rate," Huber et al., will be presented at CLEO/QELS on Thursday, May 10, at 3:45 p.m.

For more information, visit: www.mit.edu