OCT Angiography

January 16, 2016
OCT Angiography

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. 

color superficial
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.
Macleod_Billy__187013_19870603_Male_Angiography 6x6 mm_20160107081517_OD_20160107132429 - Retina.AngiographyEnface  Macleod_Billy__187013_19870603_Male_Angiography 6x6 mm_20160107081551_OD_20160107132414 - Superficial.AngiographyEnface
      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:

Kelly_Richard__brvo- Deep.AngiographyEnface   Macleod_Billy__187013_19870603_Male_Angiography 6x6 mm_20160107081419_OD_20160107132327 - Retina Depth Encoded.AngiographyEnface
          BRVO at the deep retina level            NVD on color depth encoding

Weber_William__rap - Retina Depth Encoded.AngiographyEnface   Burns_Chad__187610_19690410_Male_Angiography 3x3 mm_20160113094325_OD_20160114154915 - Retina Depth Encoded.AngiographyEnface
                                              CNV on color depth encoding

Webster_Daniel__187587_19490309_Male_Angiography 3x3 mm_20160111092102_OS_20160111164528 - Superficial.AngiographyEnface  Webster_Daniel__187587_19490309_Male_Angiography 3x3 mm_20160111092102_OS_20160111164534 - Deep.AngiographyEnface   Webster_Daniel__187587_19490309_Male_Angiography 3x3 mm_20160111092102_OS_20160111131548 - Retina Depth Encoded.AngiographyEnface
CNV on superficial retina, choriocapillaris and color depth encoding