Spectral-domain optical coherence tomography represents step forward

April 30, 2008

Spectral domain, three-dimensional (3-D), high-resolution optical coherence tomography (OCT) represents a step forward in OCT technology, with precise registration, complete data set acquisition, and improved coverage of the retina being the major advantages.

Key Points

New Orleans-Spectral domain, three-dimensional (3-D), high-resolution optical coherence tomography (OCT) represents a step forward in OCT technology, with precise registration, complete data set acquisition, and improved coverage of the retina being the major advantages, according to Jay S. Duker, MD.

"Given how important OCT is to modern clinical practice, it is interesting that the history of the technology began only slightly more than 15 years ago, with the first images obtained from a patient in 1993," recounted Dr. Duker, who described the technology at the American Academy of Ophthalmology annual meeting. He is professor and chairman, New England Eye Center, Tufts University School of Medicine, Boston.

By 1996, he said, the technology had been transferred to a company (Carl Zeiss Meditec) and commercialized. By 2002, a time-domain system (Stratus OCT, Carl Zeiss Meditec), became commercially available and soon was the international standard, Dr. Duker added. Two years later, spectral-domain OCT was reported in the literature, and many systems became commercially available.

Differences exist in the features available among the various commercially available systems, he said. For example, one system (Spectral OCT/SLO, Opko/OTI) has scanning laser ophthalmoscope microperimetry; another system (3D OCT-1000, Topcon Medical Systems) has built-in color fundus photography capability; and a third system (Spectralis, Heidelberg) provides color fundus photography, angiography, and fundus autofluorescence. All of these systems, he said, provide a rendered fundus image from the 3-D data set and eventually will allow importation of color photographs as overlays to the OCT image.

Disadvantages

A major disadvantage to this technology is cost, Dr. Duker said.

"These 3-D, high-resolution systems are more expensive than time-domain systems-by anywhere from 25% to 150% more expensive," he said.

A second challenge to overcome, he said, involves the size of the data sets; they are very large, making sequential analysis of all the B scans impractical. In addition, Dr. Duker said, storage of large data sets is problematic. Also, the quality of the images may decrease in the presence of a patient with small pupils or media opacities, he added.

Multicenter clinical trials conducted with differing OCT systems also may be problematic, Dr. Duker said. Although only one trial was involved with the time-domain OCT system, he said, now, numerous companies are involved in manufacturing high-resolution spectral-domain OCT systems (3D SDOCT, Bioptigen; Cirrus HD-OCT, Carl Zeiss Meditec; Spectralis HRA+OCT, Heidelberg Engineering; Spectral OCT/SLO, Opko/OTI; Copernicus, Optopol; RTVue-100, Optovue; and 3D OCT-1000, Topcon).

"The hardware in these systems cannot be patented," Dr. Duker said. "However, the software can make or break each of these systems. When testing systems for your practice, each system should be evaluated and the software tested to determine which works best in an individual practice."

All of these systems can perform 3-D OCT, and all can produce cube scans ranging from 4 × 4 mm to 6 × 6 mm, he said. Dr. Duker added that all systems can create the rendered fundus image that is similar to a red-free photograph and allows precise registration of a B scan to the exact point in the fundus. A full 3-D OCT image can be captured in 2 to 3 seconds, Dr. Duker said.

The future

"We are now used to looking at the posterior segment structures, such as the optic nerve and the macula, in two dimensions. Very soon, we will be used to looking at the macula in three dimensions," he said.

Clinically, 3-D, high-resolution [OCT] offers some real advantages, the first of which is that clinicians can view more than six B scans to avoid overlooking important pathologies, Dr. Duker stated. Second, he added, volumetric data analysis of the full-thickness retina, as well as the pathologies such as subretinal fluid, for example, can be performed. Also, Dr. Duker said, 3-D topographic maps of thickness of the total retina and the thickness of the inner retinal surface can be viewed. Diagnosis and planning of surgeries should be improved by the topographic evaluation, he said.

"3-D scanning facilitates precise registration with no skip areas. Volumetric evaluation of macular disease is now possible. Precise registration is possible through a rendered fundus image. Surgical interventions can be planned on a 3-D view, and these devices are now commercially available," Dr. Duker concluded.