SYMPOSIUM RECAP

Evaluating the Spectral Domain Advantage

Learn how the Cirrus HD-OCT can improve the way we evaluate, track and treat retinal disease.

By Ursula Schmidt-Erfurth, M.D.

With the introduction of spectral domain OCT, we draw ever closer to technology that provides in vivo histology. Here, I'll discuss the advantages of spectral domain technology and how they can be applied to improve treatment outcomes in retinal disease.

Key Clinical Tool

The Cirrus HD-OCT offers several advantages in clinical practice. First and foremost — it's fast, and because of its speed, we're able to obtain more data. With earlier technology, we were pleased with simply identifying the retina. With spectral domain technology, we're able to see the finer details of the retinal layers. The fine retinal and subretinal details make a significant difference if there's destruction within the retinal layers, for example, as we see with cysts or cystic degeneration, or if subretinal fluid is underlying an otherwise normal retinal anatomy. This new technology will be instrumental in monitoring patients, because it will provide more detailed information about the treatment benefit to patients.

Precise Images

The Cirrus HD-OCT provides precise images and measurements. Time domain OCT captures six lines of data and requires extrapolation. Spectral domain technology scans the area of interest with a series of parallel lines and provides a cube of complete data. No extrapolation is required.

The high definition, high resolution OCT images from Cirrus HD-OCT reveal fine details of the retinal layers that may not have been appreciated before. In one lesion, for example, we may have both subretinal fluid and RPE fluid, reminding us that we aren't dealing with homogeneous lesions.

With the cube scan, we can obtain a retinal thickness map that resembles a topographic relief map. The internal limiting membrane (ILM) layer is segmented and displayed in the ILM layer map on the Cirrus. This ILM layer map shows an ophthalmoscopic view, as if we were looking at the ILM layer en face.

We also can segment the retinal pigment epithelium (RPE), which allows us to look beneath the retina. The RPE map is essentially a 3-D topography of the RPE. This is very important for diseases that originate from the RPE or the choriocapillaris, such as central serous retinopathy or age-related macular degeneration (AMD).

With occult lesions, for example, we may be able to identify a contour of the choroidal neovascularization (CNV). This is important when we treat with antiangiogenic therapy because we want to eliminate the fluid in the retina, and we also want the lesion to become flatter and atrophic and eventually disappear.

In the future, Cirrus HD-OCT will allow volumetric detection of RPE abnormalities, so we'll be able to measure the height of the lesion as well as the extension and area, allowing us to quantify what happens at each of the different layers.

Figure 1. The Cirrus HD-OCT provides an integrated image, called the OCT fundus image, which comprises the B-scan images of the cube scan, offering precise orientation and exact registration.

The Cirrus also provides an integrated image, called the OCT fundus image (Figure 1), which comprises the B-scan images of the cube scan, offering precise orientation and exact registration. The direct correlation between the B-scan and the OCT fundus image is what really sets this technology apart from the rest.

The 3-D retinal thickness map (Figure 2) shows the topography of retinal thickness — the distance between the ILM and the RPE. The topography of the retinal thickness provides a very precise measurement of the thickness at all locations. The appearance of holes is actually a prominence of the RPE — not holes in the retinal surface. A prominence occurs, for example, when there's a retinal detachment with subretinal fluid.

Applying Spectral Domain Technology

The following cases demonstrate the utility of spectral domain OCT. In a case with multiple drusen, the Cirrus HD-OCT segmented RPE pathology from RPE physiology so we could document all of the drusen as they represent focal RPE attachments. In addition, we can uncover the RPE layer, examine it and measure the number of drusen. Further, we can measure the total drusen load, which is important in prevention studies.

With RPE detachment, we can look at the RPE disease and see where the pigment epithelium detachments are located and how high they are or how flat they become during treatment.

In occult CNV, we usually combine angiography and Stratus OCT (Carl Zeiss Meditec, Dublin, Calif.) to determine if a membrane is underlying the RPE deviation. However, with the improved resolution offered with the Cirrus HD-OCT, we may be able to see the split of the RPE membrane. We already see in very early cases when the CNV is entering the subretinal space. This is an important feature that will improve the likelihood of early detection and help us better understand occult CNV.

Cirrus HD-OCT also is instrumental in differential diagnosis as the next case illustrates. In this case, I treated a patient with retinal thickening and RPE disease. On closer examination, we could see the epiretinal membrane on the 2-D scan and the single scan, along with retinal thickening. We could see the precise configuration of the retinal thickening and retinal deformation, as well as soft drusen underlying the retinal pathology. This topography provided a 3-D look at the disease process, clearly showing radial folds and the extent of epiretinal traction. We could see that it was retinal edema or thickening resulting from traction, which wasn't related to the RPE changes we observed. We identified two different diseases in this patient — vitreomacular traction in the ILM and early AMD with large focal drusen. The technology also will be useful with other abnormalities, such as macular holes, so that we can explain to patients if surgery will improve visual acuity as opposed to simply demonstrating anatomic success.

Figure 2. The 3-D retinal thickness map shows the topography of retinal thickness — the distance between the ILM and the RPE.

OCT Technology Advances

Cirrus HD-OCT, with advanced algorithms for layer segmentation, will have a significant impact on how we treat patients clinically. Carl Zeiss Meditec is committed to the ongoing development of this technology. The company is refining the software so we'll be able to fully utilize spectral domain technology to perform measurements and segmentations more accurately.

Ursula Schmidt-Erfurth, M.D., is professor and chairman of the Department of Ophthalmology, Medical University of Vienna, Vienna, Austria.