Perspective
Spectral-Domain Optical Coherence Tomography: A Comparison of Modern High-Resolution Retinal Imaging Systems

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Purpose

To provide a review of commercially available spectral-domain optical coherence tomography (SD OCT) systems in clinical ophthalmology.

Design

Perspective.

Methods

Review of current manufacturer information, selected articles from the literature, and the authors' clinical experience.

Results

Because the premise of SD OCT technology is the nonproprietary mathematical formula of Fourier transformation, 9 different SD OCT systems currently are or soon will be commercially available. Also demonstrated are Cirrus en face C-scan visualization of photoreceptor attenuation resulting from acute zonal occult outer retinopathy and Spectral OCT/scanning laser ophthalmoscopy microperimetric analysis of a macular caldera lesion resulting from North Carolina macular dystrophy.

Conclusions

Advances in high-resolution imaging of the anterior and posterior segment have revealed new in vivo details of anatomic, physiologic, and pathologic data for the practice of ophthalmology. Compared with time-domain OCT, SD OCT tends to derive increased retinal thickness and decreased nerve fiber layer thickness measurements. This is likely because of increased depth of resolution and greater volume of data acquired with each scan. Interdevice comparison is not practical because of differences in individual segment boundary algorithms. Improvements in photoreceptor inner segment–outer segment layer visualization should aid our understanding of visual dysfunction in a variety of retinal pathologic features. As the technology develops, SD OCT will continue to provide new insights about ocular structure and disease.

Section snippets

Cirrus HD-OCT and Visante

Cirrus OCT (Carl Zeiss Meditec) is an SD OCT platform that has a 5-μm axial resolution and scans at 27 000 A-scans per second. The system combines a small hardware footprint with advanced optics and a nonmydriatic camera. Device operation is facilitated by an on-screen iris viewer that allows mouse-driven alignment without the need for joystick control or much hardware movement, as is the case with its predecessor, the Stratus OCT. On-screen targeting software enables the operator to move the

Spectralis

Spectralis (Heidelberg Engineering, Vista, California, USA) combines a scanning laser ophthalmoscope (SLO) with OCT to produce tracking laser tomography that has a 7-μm axial resolution and scans at 40 000 A-scans per second. One beam constantly images and tracks the fundus and acts as a reference, guiding the second beam of light precisely to position the cross-sectional OCT scan. This real-time eye tracking enables a highly repeatable alignment of OCT and fundus images that can be displayed

RTVue-100

RTVue-100 (Optovue, Fremont, California, USA) has a 5-μm axial resolution and scans at 26 000 A-scans per second. It allows the option of a 5 × 5-line raster scan, sampled 5 times each for noise reduction, a 6 × 6-mm grid scan, or en face 3D scanning capability, all of which are automatically registered to an Early Treatment Diabetic Retinopathy chart. Users also can generate single 12-mm long scans, which can be patched together to make a high-resolution map of the posterior pole. Current

3D-OCT 1000

3D-OCT 1000 (Topcon, Paramus, New Jersey, USA) has a 6-μm axial resolution and scans at 18 000 A-scans per second. Posterior segment acquisition options include a 6 × 6-mm, 4.5 × 4.5-mm, or 3 × 3-mm volume cube scans, as well as a 3D rendering mode.

The integration of a 3.15-megapixel nonmydriatic camera is a unique aspect of the system that allows color fundus photographs as well as OCT images to be acquired for both retinal thickness and glaucoma analysis (Figure 4). Specialized software

Spectral OCT and SLO

Similar to the Spectralis, the Spectral OCT/SLO (OPKO/OTI, Miami, Florida, USA) is a combination OCT and confocal SLO designed to image vitreous, retinal, and choroidal structures for accurate, point-to-point registration and orientation. It has a 5-μm axial resolution and scans at 27 000 A-scans per second. The tomography map is produced from a sequence of B-scans, and the macular analysis is viewed as 5 × 5 or 8 × 8 square grids over 6 × 6 mm. Retinal maps can be viewed as a 3D volume cube,

SOCT Copernicus and SOCT Copernicus HR/SPOCT

The SOCT Copernicus (Optopol, Zawiercie, Poland) has a 6-μm axial resolution and scans at 25 000 A-scans per second (Figure 6). It has a 10-mm B-scan width and allows single or customizable 6-line radial scans, as well as 3D volume cube rendering. Anterior segment analysis of cornea, iris, and lens also is available. The device incorporates a retinal tracking system, and posterior segment analysis includes retinal thickness and RPE mapping, 3D cross-section animation software, NFL thickness

Bioptigen SDOCT

The Bioptigen SDOCT (Bioptigen, Durham, North Carolina, USA) system uses high-throughput spectral interferometry to produce real-time images of ocular tissue microstructure with 4-μm axial resolution to scan at 20 000 A-scans per second. For adult and pediatric patients, up to a 10 × 10-mm retinal area of each eye can be acquired in fewer than 6 seconds, with oversampling along the lateral axis and no more than 80-μm spacing between B-scans. It is FDA approved to acquire, process, display, and

Retinascan RS-3000

Nidek (Gamagori, Japan) has initiated a European launch of its SD OCT device, expected to be demonstrated at the Seventeenth Congress of the European Society of Ophthalmology in June 2009. According to a premeeting advertisement, the device features real-time SLO imagining with up to 53 000 A-scans per second obtained over 1.6 seconds. One intriguing aspect of the device is the ability to provide segmentation and visualization of the retina into 6 distinct layers, including the internal

Discussion

OCT has become a critical tool for ophthalmologic clinical and surgical decision making. For example, the application of OCT as a diagnostic adjuvant to clinical examination of vitreoretinal interface pathologic features, including macular hole, vitreomacular traction, and epiretinal membrane, has been well documented for time-domain OCT.45 In our experience, and according to other reports,33, 38, 43, 46 SD OCT provides even more detailed information about the vitreoretinal interface in such

Conclusions: The Future of Optical Coherence Tomography

The advent of SD technology has allowed extensive amounts of new anatomic, physiologic, and pathologic data to become available routinely for the practice of ophthalmology. Although the current literature is still relatively sparse regarding how these data can improve patient care directly compared with time-domain technology, it is clear that large amounts of in vivo information can be acquired without invasive intervention, effectively allowing a virtual biopsy, as originally envisioned by

Daniel F. Kiernan, MD, is a vitreoretinal fellow at the Illinois Eye and Ear Infirmary, University of Illinois at Chicago and completed his ophthalmology residency at the University of Chicago, Pritzker School of Medicine. He received his undergraduate education at the University of Chicago and his medical degree from the Chicago Medical School. His research interests include ophthalmic imaging, age-related macular degeneration and hereditary macular diseases.

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  • Cited by (0)

    Daniel F. Kiernan, MD, is a vitreoretinal fellow at the Illinois Eye and Ear Infirmary, University of Illinois at Chicago and completed his ophthalmology residency at the University of Chicago, Pritzker School of Medicine. He received his undergraduate education at the University of Chicago and his medical degree from the Chicago Medical School. His research interests include ophthalmic imaging, age-related macular degeneration and hereditary macular diseases.

    Seenu M. Hariprasad, MD, is Associate Professor of Ophthalmology at the University of Chicago, Pritzker School of Medicine, where he serves as Chief of the Vitreoretinal Service, Director of the Surgical Retina Fellowship Program and Director of Clinical Research. He has been involved in national clinical trials evaluating new drugs, devices, and surgical innovations for diseases of the retina. In 2007, the Consumer Research Council of America selected him as one of “America's Top Ophthalmologists.”

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