The technology of retinal imaging has advanced rapidly in recent years with the introduction of instruments that measure data points at increasingly greater densities. Optical coherence tomography (OCT), introduced in the 1990s,1 has already undergone several iterations. Most notably, spectraldomain OCT technology, introduced in the middle years of this decade,2,3 produces higher-resolution images than the earlier time-domain OCT technology, and its higher acquisition speed has allowed the creation of high-quality 3-D retinal reconstructions.

The pairing of OCT with scanning laser ophthalmoscopy (SLO) technology was first described in 2000.4 This combination allowed point-to-point correspondence of OCT slices with retinal landmarks and made serial OCT imaging possible. Opko (formerly OTI; Miami, FL) was one of the companies that pioneered the combination of these imaging modalities with its OCT/SLO, and recently with its Spectral OCT/SLO System.

The combination of these technologies has now taken another leap forward with the introduction by Opko of variable-field SLO and ultra high-speed OCT. This instrument brings the capabilities of these technologies to a whole new level.

The integrated OCT/SLO imaging system is capable of adjusting from a scanning field of 15 mm down to less than 300 µm. The optical system has been modified to allow high-resolution confocal microscopy of the retina. An ultrafast OCT spectrometer is capable of capturing 100,000 to 200,000 A-scans per second, which equates to highspeed, high-resolution imaging at 100 to 200 frames per second. Amazingly, all of this additional capability still fits in the same compact clinical footprint as Opko's Spectral OCT/SLO.

The system allows nonmydriatic widefield confocal retinal imaging. During real-time widefield scanning, the system's software allows the user to select any point of interest for closer viewing by placing a red square around the area. With the device's SLO optical zoom capability, the area of interest defined by the square is then rescanned and presented at greater magnification (Figure 1). The confocal SLO is capable of zooming in to an area as small as 280 by 280 µm (Figure 2).

The instrument can also perform quantitative analysis in a selected field, for instance counting the number of cells in a microscanned area (Figure 3). The software allows analysis, measurement, cell counting, and comparison of cellular structures.

The C-scan mode allows the user to view slices at various depths in the retinal tissue, to examine structures including the larger retinal vessels in the retinal nerve fiber layer (Figure 4), the superficial and deep capillary beds at mid-retinal depth (Figure 5), and the retinal pigment epithelium and choriocapillaris deeper in the retina (Figure 6). These C-scans can also be zoomed to show greater detail (Figure 7).

There are some limitations to the technology. Patient movement due to fixation loss can disrupt acquisition of the smallfield SLO scans. Variations in the tear film can lead to variability of focus in the smallfield scans. In addition, the dataset for the tomographic images is very large, and the device requires a skilled operator.

Despite these limitations, the technology represents a significant step forward in clinical imaging power. The ability to zoom in on small lesions gives the clinician an unprecedented histologic view of the retina in vivo. The C-scan tomographic OCT capability allows “dissection” of the retina to different depths in a clinically familiar format. And the ability to count and analyze cellular density offers the promise of earlier detection of pathology, before clinical signs are present.

Richard B. Rosen, MD, is Vice Chair and Surgeon Director and Director of Ophthalmology Research at the New York Eye and Ear Infirmary and a Professor of Ophthalmology at New York Medical College. Dr. Rosen states that he is a member of the scientific advisory board of Opko/OTI. He can be reached via e-mail at rrosen@nyee.edu.

  1. Izatt JA, Hee MR, Swanson EA, et al. Micrometer-scale resolution imaging of the anterior eye in vivo with optical coherence tomography. Arch Ophthalmol. 1994;112(12):1584–1589.
  2. Wojtkowski M, Srinivasan V, Ko T, Fujimoto J, Kowalczyk A, Duker J. Ultrahigh-resolution, high-speed, Fourier domain optical coherence tomography and methods for dispersion compensation. Opt Express. 2004 31;12(11):2404–2422.
  3. Cense B, Nassif N, Chen T, et al. Ultrahigh-resolution high-speed retinal imaging using spectral-domain optical coherence tomography. Opt Express. 2004;12(11):2435–2447.
  4. Podoleanu A, Rogers J, Jackson D, Dunne S. Three dimensional OCT images from retina and skin. Opt Express. 2000;7(9):292–298.