Spectral-domain optical coherence tomography has practical applications in the diagnosis, management of retinal disease

February 1, 2009
Ilya Petrou, MD

Spectral-domain optical coherence tomography is becoming an invaluable diagnostic tool and greatly helps ophthalmologists better manage their patients' conditions, according to one expert. This improved management of conditions, he said, can be realized not only in the medical arena but also in the surgical arena as well.

Key Points

According to Dr. Heier, a vitreoretinal surgeon at Ophthalmic Consultants of Boston, specific spectral-domain optical coherence tomography (SD-OCT) technology (Spectralis, Heidelberg Engineering) is leading the way in this retinal revolution, redefining not only how ophthalmologists diagnose diseases but also how they manage them.

"As we become more familiar with SD-OCT and increasingly aware of the capabilities of this imaging technique, I think that we are learning more about disease states, which, in turn, allows us to become better diagnosticians," he said. "This cutting-edge technology is helping us both to diagnose and manage disease better."

In the past, barring obvious disease, it was not uncommon for ophthalmologists to be challenged in finding minute pathology when examining a patient who presented with central vision complaints, Dr. Heier said. Changes in the retinal pigment epithelium (RPE) or photoreceptors may have been noticed if grossly abnormal, but otherwise, subtle pathology often would go unnoticed.

Now, however, ophthalmologists can observe small changes in the photoreceptor layer or very subtle abnormalities in the RPE, which, before the advent of the SD-OCT, were poorly or infrequently detected. Moreover, these subtle changes are reproducible.

The aforementioned SD-OCT technology not only clearly demonstrates these subtle nuances of pathology but also allows them to be closely monitored, he said. Novel eye-tracking and reference line features integrated into the device allow the clinician to be sure that the same exact area is being examined at every visit, regardless of the underlying pathology, Dr. Heier added.

SD-OCT slowly is becoming irreplaceable technology in the management of age-related macular degeneration, he said, because ophthalmologists now have the unprecedented ability to return to an area with confidence that it is the same area first examined. This close monitoring of a patient's disease is likely to increase the ability of the clinician to manage patients' conditions better and can play a crucial role in reaching decisions regarding the commencement of therapy, Dr. Heier said. Although this ability has yet to be demonstrated-or studied-in a large trial, most specialists believe it will lead to better outcomes, he added.

Secondary tissue loss

With new software, these subtle changes in pathology also may include the assessment of the retinal nerve fiber layer and its loss, allowing evaluation of tissue loss secondary to diseases such as glaucoma and vascular disease.

"When we talk about managing macular degeneration, many of us, if not most of us, are managing the disease after the initial diagnosis with the use of OCT, and we are managing it by the presence or absence of fluid," Dr. Heier said. "We can now do volume scans and are able to assess larger areas with a great degree of confidence that we are not missing new areas of pathology."

Prior to the advent of this SD-OCT device, older technology such as time-domain OCT (TD-OCT) was considered the gold standard, he said. TD-OCT, however, often was unreliable in detecting pathology, because the device only scanned limited points in the retina, Dr. Heier said. Today, continued visual complaints by the patient would lead to a volume scan with SD-OCT technology, often resulting in the detection of subtle pathology, he added.

Although increasingly practices are investing in the newer SD-OCT devices, TD-OCT is not obsolete, Dr. Heier said. Practices involved in clinical trials still must have TD-OCT technology, because there is no current standardization for SD-OCT devices.

Studies show that the various SD-OCT devices yield different baseline retinal thickness measurements because they each measure the thickness of the retina at different points, he said.

All of the devices start at the inner aspect of the retina in a relatively standardized manner, but they each measure the other layers differently, either starting from the internal face, middle, or external face of the RPE, resulting in differences in the measured retinal thickness based on the particular OCT device used.

"A consensus regarding standardization is important, and OCT reading centers are currently in collaboration trying to establish standardization," Dr. Heier said. "From the point of the individual clinician, however, the important issue is essentially to have reproducibility within your own clinic. If you are using quantitative measurements to help you guide your decisions, you have to look at your own OCT and understand what those measurements represent and at the same time be willing to ensure that those measurements are being taken from similar regions."

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