BLOG: Should I use OCT angiography?
It’s mid-October as I write this, and I’m at home watching this year’s online American Academy of Optometry sessions.
I’ve noticed that there are several OCT angiography (OCTA) lectures this year, and, in fact, each year there seem to be more talks about this new technology.
I just watched Julie Rodman, OD, MS, FAAO, from Nova Southeastern University, give an excellent OCTA lecture where I learned a lot of new information, and I wanted to revisit this topic as my uses of this technology have evolved over the years. I first wrote about OCTA in these pages in 2016, before our hospital even had the technology, and since then we’ve acquired a device and we’ve been using it more and more. In adapting this technology, I’ve been reminded of our profession’s adaptation to time domain OCT and then spectral domain OCT.
With both of those rollouts, some doctors are quick to test the technology and incorporate the new data into their patient management. There were also doctors who (at first) politely declined using the new tech, preferring their time-tested clinical acumen and observation skills vs. a new machine with some flaws.
To my eyes, the difference between these types of doctors did not follow age, gender or disease-specialty factions; the difference was more related to personality — who was more likely to think outside their box. I see OCTA as the next manifestation of technology our profession will eventually widely embrace.
When I first heard the description of how this technology works, I thought of photography. I first bought an SLR camera around a dozen years ago, and I’ve been photographing landscapes and birds ever since. In photography (to simplify a complex subject), there are many differences between shutter speed (or time) priority and aperture priority in the camera settings. To summarize aperture priority: the camera will allow the user to set the aperture of the camera (essentially the depth of the image) and automatically choose the best shutter speed to capture the image without motion blur. To summarize shutter speed priority: the user chooses how dramatically to freeze the movement and allows the camera to choose the depth. The example I think of is a hummingbird’s wings. A fast shutter speed will capture the wings in perfect, crisp stillness; a slow shutter speed will create an artistic blur of the wings.
OCTA is essentially shooting a picture of a fundus using a fast shutter speed. The technology tracks the fundus, ensuring the image “stays still” so that the only thing in motion is red blood cells moving through the vessels. Then it renders an image of just the things moving over the series, ie, red blood cells in vessels. This movement occurs in the larger arterioles but also in the much smaller capillaries. So, conditions like capillary non-perfusion (like in diabetes or vascular occlusion) will show up as dark (or no movement), and conditions like choroidal neovascular membranes (CNVMs) will show up with more color than usual (signifying too much blood flow). OCTA also does a great job segmenting the layers of the retina, allowing the clinician to pinpoint the problem. While this can be accomplished in fundus fluorescein angiography, it can be difficult with some diseases to see in which layer lies the anomaly.
I’ll wrap up this discussion by writing about two clinical pearls I’ve learned about OCTA. First, enlargement of the foveal avascular zone (FAZ) in patients with diabetes is much more common than I previously thought. Sometimes a clinical exam seems normal, and then the OCTA reveals some mild FAZ expansion. This is best seen as changes over time, as opposed to a snapshot in time (pardon the photography pun). If you see a patient with diabetes who is not correctable to 20/20, and the OCT shows no macular edema, then looking for FAZ enlargement with OCTA would be warranted.
The second pearl I’ve learned is that mild CNVMs are much more common than I previously thought. There have been times when I’ve noticed some retinal pigment epithelium thickening/changes in my age-related macular degeneration patients, and I thought it was just some drusenoid pigment epithelial detachment. But an OCTA reveals some irregularly high blood flow in small choroidal vessels, indicating the start of a CNVM.
So, if you are lucky enough to have an OCTA in your practice, use it! Be like the first clinician I wrote about: embrace and explore the new technology. You might be the one who discovers a new imaging finding that indicates a disease process. Then name it after yourself and be famous! Over the coming years, someone will uncover new signs, and it might as well be you.