Advances in spectral domain 3-D high-resolution OCT

Spectral domain optical coherence tomography (SD-OCT), the latest generation of the technology, is a breakthrough because it has dramatically cut the time required to obtain images by eliminating the moving mirror that was a component of standard OCT, according to Cynthia Toth, MD.

In addition to being 50 times faster than conventional OCT, SD-OCT has improved resolution because of improved processing. Another benefit is decreased patient movement artifact, especially in pediatric patients.

"In age-related macular degeneration, there is often motion artifact. It is difficult to sort out drusen and differentiate them from patient motion that could be either or a pigment epithelial defect or normal retinal pigment epithelium (RPE) choroid. Using SD OCT it is easier to isolate drusen from the underlying baseline RPE and to define whether pigment epithelial detachments or RPE abnormalities are present," Dr. Toth stated. She is professor of ophthalmology, Duke University Medical Center, Durham, NC.

The SD-OCT data can be integrated with the information obtained from angiography and fundus examinations, which allows identification of the location of an abnormality found on OCT. "One benefit of SD-OCT is the creation of the summed voxel projection (SVP), which is helpful for orientation of individual OCT scans. One can collapse 3-D OCT volumes along the depth axis to form a 2-D plane, summing pixels to calculate one representative pixel intensity along each line in the projection," she explained. As a result of prominent shadowing from the retinal vasculature, the SVP image is similar to a fundus photograph and this image can be used to orient the SD-OCT image to a fundus image.

Drawbacks of the technology include large datasets, the need to integrate data with conventional imaging, and normative data are required for the new systems, there are a number of systems from which to choose. An advantage is the availability of portable systems.

"Three-dimensional SD-OCT offers the potential to identify biomarkers and measure changes in disease over time. For clinical and research use, improved methods are needed to export, analyze, summarize, and manage data. These are on the way," Dr. Toth concluded.