January 16, 2016
In my 27 years in ophthalmology, there have been a few watershed moments that stand out. In the early nineties, it was the transition to digital imaging, followed quickly by ICG angiography. In the late nineties, I was fortunate to witness the early advent of OCT, and was in the room when the results of the Marina and Anchor studies, which brought anti-VEGF therapy into the office, was announced.
At the American Academy of Ophthalmology Annual Meeting in Chicago in 2014, you would be hard pressed to find much information on OCT angiography (OCTA). At the meeting in Las Vegas this past Fall, OCTA was the topic of most conversations. At the time of this writing, the only FDA approved OCTA is the Zeiss Angioplex. I have used the Zeiss Angioplex system in clinic since the beginning of this year, and wanted to share some of my preliminary thoughts.
First, I have to keep reminding myself that we are in the pioneering stage of OCTA, and therefore rules have yet to be established. There are no set protocols for scanning; it will take some time to create those, and will vary by practice. Second, because we are in the pioneering stage, we don’t really know what we are seeing. As was the case in the early days of OCT, pathology presents itself differently than what we’ve become used to. We have to not only identify what is normal, but also come up with accepted nomenclature for everything we see on the images.
Using en-face visualization of the layers in the retina, the OCTA detects flow in the retinal vessels, to the capillary level, by identifying movement in the posterior pole. The algorithm assigns white color to movement and black to non-movement, which gives the image the appearance of a fluorescein angiogram. The Angioplex system allows for the option of color depth encoding, which assigns color to the vessels according to their depth in the retinal or sub retinal layers. The easiest way to describe OCTA is this:
Standard OCT displays anatomy, OCTA displays function.
Normal retina. The color depth encoding image assigns color according to the depth of the vessels. Using en-face imaging, you can visualize vessels at the superficial, deep, avascular, choriocapillaris and choroidal level
Angioplex is built on the foundation of the Zeiss Cirrus OCT, which also allows for visualization of the en-face images of the retina. Coupled with their spectral domain OCT, I am able to produce line scans, raster scans, volumetric OCT, etc, along with the accompanying OCTA images. The movie mode displays each layer of the en-face scan IN OCTA mode, so I can find subtle changes in the angiogram and correlate it with the OCT scan.
There are some restrictions to the technology at this point. OCTA can not detect staining or pooling of fluid. For instance, if a patient presents with sub retinal fluid secondary to AMD or CSCR, but there is no active leakage, the OCTA may present as normal. The other major restriction is the lack of wide angle imaging. Presently, the Angioplex system allows for 3mmx3mm or 6mmx6mm, although future applications may include 8×8 and 12×12.
6 x 6 scan of non perfusion same patient, scanned with 3 x 3
The downside to being “ahead of the curve” is that the network of users is limited. The advantage is that you can be a part of establishing protocol for new technology; protocols that become standard across the country.
As I become more familiar with the technology, I will continue to post blogs updating my progress. Here are some images from the past week:
BRVO at the deep retina level NVD on color depth encoding
CNV on color depth encoding
CNV on superficial retina, choriocapillaris and color depth encoding