In the first episode of Clinical Conversations in Retina, Carolyn Majcher, OD, FAAO, and Daniel Epshtein, OD, FAAO, discuss which diseases they use optical coherence tomography angiography (OCTA) for most often and how they incorporate OCTA in clinical practice on a day to day basis.
Clinical applications for OCT angiography
To start, Dr. Majcher highlighted that she most often uses OCTA to evaluate patients with diabetic retinopathy (DR) and age-related macular degeneration (AMD), as it aids in detecting neovascularization as early as possible. This is valuable because the earlier that neovascularization is caught, the better the visual outcome might be for the patient, added Dr. Epshtein.
For diabetic patients, Dr. Majcher explained that she starts looking for early proliferation on OCTA in patients that have been clinically staged as severe nonproliferative DR (NPDR), and at that point, she initiates a montage OCTA, which covers a 14 x 14mm area. This allows her to visualize the arcades and a little outside in the midperipheral space, as that is where she most often finds neovascularization on the border between perfused and nonperfused retinas.
Additionally, she uses a 3 x 3mm OCTA scan of the macula to look for macular ischemia. While this can occur at any stage of DR, she sees it most often in more severe stages. If a patient does report a decrease in vision that she cannot explain and there is no presence of macular edema, she will likely perform a 3 x 3mm scan of the foveal avascular zone (FAZ).
Dr. Epshtein remarked that clinicians are lucky to have the montage feature on OCTA now because when OCTA first came out, in order to get a comprehensive scan, it was necessary to perform multiple scans and then mentally stitch them together to get a broad view of the posterior pole.
Visualizing pre-clinical NPDR on OCTA
In terms of clinical efficiency, Dr. Majcher noted that she doesn’t tend to perform OCTA on diabetic patients unless she sees clinical signs of DR, but OCTA can be very helpful for these patients as an educational resource.
For example, if a patient’s hemoglobin A1C (HbA1c) levels are at 12% and there haven’t been significant clinical signs of diabetic retinopathy, using OCTA to detect early changes may show the patient how the disease functionally and structurally impacts their vision and eye which can be a powerful educational tool.
Dr. Epshtein agreed, saying that even for patients who are not high-risk clinically but have had chronically high HbA1c levels, OCTA aids in demonstrating the damage done to the retina that DR is causing and how it may progress over time, which could eventually affect their functional vision in the long-term.
Evaluating proliferative DR patients with OCTA
For patients with suspected early proliferative DR (PDR), Dr. Majcher prefers to use the vitreoretinal interface slab on OCTA because it shows the blood flow anterior to the retina. Consequently, this is where she focuses her attention on diseases that would be at risk of preretinal neovascularization, including retinal vein occlusion (RVO) and DR.
Dr. Epshtein added that when he looks at the foveal avascular zone in diabetic patients, he uses the retina slab, but when he is looking for neovascularization in PDR and RVO patients, he prefers to use the vitreoretinal slab. He finds the vitreoretinal slab to be particularly helpful because, in a normal patient, the slab should appear completely black, so if anything does show up in the scan at all, that is a clear sign to the clinician that there is some neovascular issue.
Assessing AMD patients with OCTA
Once a patient reaches the intermediate stage of nonexudative AMD, Dr. Majcher remarked that she will initiate a battery of imaging, including OCT, OCTA, color fundus photography, and fundus autofluorescence (FAF). She added that her scan protocol for OCTA depends on how many risk factors have been identified for the AMD patient during the clinical examination.
If there is any retinal pigment epithelium (RPE) detachment that she can visualize on structural OCT, she trains her focus toward the OCTA scan in that area to see if there is a sub-RPE type 1 neovascular membrane under the RPE detachment. As such, for Dr. Majcher, the location of OCTA scans tends to be influenced by the patient’s clinical presentation and any findings from structural OCT, whether it is 3mm, 6mm, or both.
Dr. Epshtein validated this, explaining that often it can be tempting to create a protocol to simplify the process, but ultimately, every patient has individual needs, so using the patient’s anatomy to guide the process is key to providing the best patient care.
Occasionally, when Dr. Epshtein sees neovascular AMD (nAMD) patients or high-risk intermediate AMD patients, he runs an OCTA scan that first focuses on the fovea, and then if there are any concerning findings, he moves the scan locus; using this method he has found peri-macular damage in nAMD patients.
Imaging nonexudative nAMD with OCTA
Nonexudative neovascularization has become a hot topic in AMD circles. It goes by several different names, such as dormant choroidal neovascularization (CNV), quiescent CNV, and nonexudative CNV, which is the term that Dr. Majcher tends to use. Interestingly, clinicians did not know that this entity existed until OCTA imaging was available because it directly visualizes the membrane itself, rather than simply the secondary exudative side effects, such as fluid or blood, seen in clinical examination.
Consequently, OCTA has opened the door for clinicians to understand that it is possible for patients to have nAMD that is nonexudative. This condition poses a high-risk that the patient may become exudative in the future, though it may not warrant anti-vascular endothelial growth factor (VEGF) treatment at that moment.
She monitors these patients closely, with follow-ups at least every 3 months when she sees the presence of nonexudative CNV. During these follow-up visits, Dr. Majcher performs both structural OCT and OCT-A to understand whether the data is repeatable or if progression might be noted on those scans.
Monitoring nonexudative nAMD patients with OCTA
For patients that she has seen convert to an exudative form of the disease, the membrane changes in morphology, which is why she performs extra OCTA scans to help train herself to identify what active neovascularization looks like on OCTA versus inactive neovascularization.
Dr. Epshtein added that for these nonexudative neovascular patients, he has found it can be common to miss this diagnosis on clinical examination, and because these patients are at high risk for converting to exudative neovascularization, it’s imperative to perform these scans on a regular basis based on case presentation.
“To treat these patients, Dr. Epshtein follows up frequently, as often as 6 weeks initially, especially if the fellow eye has marked neovascularization.”
He has noticed that these membranes can possibly grow wider and larger in size before they begin to leak, which makes this one of the signs that he specifically looks out for in OCTA scans. Dr. Majcher added that she tends to see lacy, looping capillaries on the margin or fringe of the membrane that look similar to leaves on a tree.
Dr. Epshtein highlighted that he is often surprised to see where the fluid accumulates. While clinicians might think that it would accumulate in the area with the highest amount of neovascular vessels, in fact, based on his clinical experience, it might be more random in its presentation, likely due to compromised retinal integrity and not that of the neovascular membrane vessels.
Using OCTA to visualize pachychoroid conditions
Pachychoroid conditions is an umbrella term to describe central serous chorioretinopathy (CSCR) and similar diseases. Dr. Majcher highlighted that she has been shocked to see patients with clear neovascular membranes that she would have otherwise not noticed. Similarly, Dr. Epshtein has been equally surprised to see how many of these patients have areas of neovascularization, and simultaneously seeing how either slowly the neovascularization grows or that it doesn’t grow at all.
Another disease where OCTA is very valuable is macular telangiectasia type 2 (MacTel), added Dr. Majcher. OCTA helps to delineate the vessel structure so that the clinician doesn’t have to only rely using the areas of atrophy or inner retinal cysts to identify the disease.
Therefore, OCTA has helped Dr. Majcher make the diagnosis on many occasions, even in early-stage patients where the vision is slightly reduced with minor photoreceptor loss on structural OCT. When performing the OCTA, it becomes easier to identify that the FAZ is enlarged toward the temporal aspect of the fovea, and the presence of dilated telangiectatic vessels, to better understand why the patient’s vision may be reduced.
There was also an instance where she caught subretinal neovascularization as a result, which she then referred to an ophthalmologist for anti-VEGF therapy. Dr. Epshtein added that he has noticed that the temporal vasculature becomes “scrunched” together in MacTel, so it is possible to see that there is not only FAZ enlargement but a change in the morphology as well.
Conclusion
OCT angiography is a valuable and useful tool for eyecare practitioners (ECPs) to visualize and monitor a broad range of diseases, such as diabetic retinopathy, AMD, the spectrum of pachychoroid conditions, and MacTel.
As OCTA technology continues to evolve, it has become a crucial addition to the ECP’s armamentarium, allowing for early detection of retinal diseases to provide patients with the highest level of care.
