OCT evolution provides improving resolution, speed, and clinical applications

Optical coherence tomography (OCT) continues to evolve and improve, offering clinicians more detailed information on the status of patients' eyes. Joel Shuman, MD, University of Pennsylvania Medical Center Eye Center, University of Pittsburgh School of Medicine, and a co-inventor of OCT, reviewed the technology and contrasted the first-generation technology with spectral domain technology.

"With spectral domain OCT, we can get much faster acquisition rates at about 16,000 to 40,000 A-scans per second and high resolution by broadening the bandwidth at about 5 or 6 µm or higher at about 3 to 5 µm," Dr. Shuman said. "High-speed OCT allows us to acquire the A-scans simultaneously and to collect more information at the same time."

As one of numerous examples of advanced OCT instrumentation's capabilities, Dr. Shuman reviewed a case of glaucoma in which imaging was obtained with standard OCT and contrasted the details obtained with spectral imaging.

Abnormalities not seen on Stratus OCT (Carl Zeiss Meditec), such as a small retinal nerve fiber layer defect extending from the optic nerve head, were well-defined on spectral domain OCT. Minute structural changes, such as photoreceptors hanging into the subretinal fluid space are now visible. In age-related macular degeneration, drusen can be seen deforming the retinal pigment epithelium. Anterior segment imaging also is possible, with the area of intrastromal corneal implants (Intacs, Addition Technology) and the resultant surrounding stress lines visible, as well as epithelial ingrowth after LASIK.

Another variation of OCT is swept-source OCT that captures data by using a laser to sweep through a series of wavelengths, rather than a spectrometer. This technology is limited in resolution, but is ten times faster than spectral domain OCT and 500 times faster than Stratus OCT, according to Dr. Shuman.

He also showed development of zebrafish embryos at 24, 48, 72, and 120 hours after fertilization, at which points increasingly detailed images were available. The beating heart of the animal was seen without blood flow at about 24 hours and compared with the 120-hour image of the beating heart in which the bulbous arteriosus was visible.

"The improvements in OCT may lead to better reproducibility, sensitivity, and specificity," Dr. Shuman said. "The development of the technology has been difficult, and each time the resolution improves the step is challenging and requires great effort.

"The advances allow visualization of structures not previously available and segmentation of the retinal and intraretinal layers," Dr. Shuman concluded. "OCT is a robust technology that continues to evolve. It is a useful tool for diagnosing and managing of disease and may be a cost-effective diagnostic tool for basic and clinical studies of disease."