Managing CNV With OCTA
Monitoring of exudative AMD at its best.
Optical coherence tomography angiography (OCTA) is an emerging imaging technique that provides a clear visualization of blood flow both in retinal and choroidal tissue. This technology is able to obtain depth resolved images of a given retinal or choroidal tissue and provide a layer-by-layer visualization of the entire choroidal neovascularization (CNV). Today, I would like to discuss diagnosis and follow-up of CNV with Triton Swept Source Optical Coherence Tomography – Angiography (Topcon). Swept source-OCT (SS-OCT) dye-free angiography is a transformative approach to imaging ocular vessels based on flow, as opposed to simple reflectance intensity.
This innovative technology is excellent for noninvasive monitoring of the exudative age-related macular degeneration (AMD) because both functional blood flow and morphological fluid accumulation information is provided from a single scan. Such simultaneous monitoring, based both on OCTA activity criteria and structural OCT findings, may help in the diagnosis of CNV, guiding decisions for treatment, as well as in monitoring the evolution of CNV and its response to treatment.
Structural and high-resolution OCT-B is effective for identifying exudative reaction and ICG-A to have the exact total CNV extension. The hyper-flow signal corresponding to active CNV can be obtained quickly and easily and without dye; the type of CNV can be detected and analyzed on different segmentations.
Multimodal imaging of type II CNV shows leakage on fluorescein angiography (FA), and indocyanine green angiography (ICGA) eliminates retinal angiomatous proliferation (RAP) or polypoidal choroidal vasculopathy (PVC). Structural OCT-B shows pigment epithelial detachment (PED) and subretinal hyper-reflective exudation (SHE) on high resolution. Topcon OCTA gives a wonderful hyper signal in a few seconds with good tracking.
Active CNV Criteria
OCTA activity criteria of CNV were described by Professor Gabriel Coscas, MD, and colleagues with Heidelberg technology 2 years ago.1
Shape: A well-defined CNV lesion (tortuous lacy-wheel shaped).
Branching pattern: Numerous tiny capillaries.
Anastomoses: Presence of anastomoses and loops.
Morphology of the vessel termini: Presence of a peripheral arcade.
Perilesional Halo: Presence of a perilesional hypo-intense halo, considered as regions of choriocapillaris alteration.
These criteria provide a basis for analyzation and evaluation of CNV activity and the degree of CNV proliferation, persistence and/or recurrence; conversely, they provide for the stabilization and healing with vessels that become mature or quiescent.
Furthermore, last year we evaluated split-spectrum amplitude-decorrelation angiography (SSADA) technology with COFT-1 and found that the sensitivity and the specificity were excellent. We found the same parameters with Topcon instruments using the full spectrum algorithm with analysis ratio. OCTA criteria for active CNV are lacy wheel shaped with multiple anastomoses and loops, dense branching, peripheral arcade, and hyper-intense perilesional halo on Bruch segmentation. The presence of anastomoses and loops, numerous branching and tiny capillaries, and the presence of a peripheral arcade are easily detectable at diagnosis and during follow-up.
This technology enables us to recognize type II CNV based on the appearance of dense branching and numerous tiny capillaries with a complete peripheral vascular arcade. Hemorrhages are detectable on color images, fluid is visible on the OCT-B scan, and leakage is visible on the fluorescein angiograph (FA). The imaging modalities are all included in the complete version of Topcon’s SS-OCT angiography. OCTA allows complete description of the CNV activity and CNV type.
When initially diagnosing CNV, we have these criteria of activity: sea-fan shape, multiple anastomoses and loops, branching, peripheral arcade, and perilesional halo. After injection, we have these criteria of quiescence: absence of a defined shape, no branching, only large and voluminous mature vessels without anastomoses, no loops, no arcade, and no peri-lesional halo.
DRI OCT Triton SS OCTA fosters effective follow-up and treatment with a point-by-point post-processing tracker. For example, after a loading dose of anti-VEGF, we might observe dramatic decrease in hyper signal, hyper flow, and PED. We may continue to inject until visual acuity is stable. In another instance, if after 3 months we observe persistence of partial peripheral arcade, we would continue to inject, and then if after 4- and 6-month follow-ups we observe regression of loops, branching, and vessel termini, we would adapt the rhythm of injection to those findings.
In routine practice, when patients ask if a treated lesion is still active, we can respond by checking the criteria. If we have, for instance, a well-defined shape, few anastomoses, and partial peripheral arcade, the CNV is still active with three of five essential criteria corresponding to fluid persistence on OCT-B scan. A closer look at the still active hyper-signal on the OCT-B scan indicates no colorized flow, indicating that it is an inactive lesion. CNV activity offers diagnosis guidance, but OCTA enables a customized follow-up approach. We can adapt the rhythm of injections with more qualitative information (Figure). When improvement is seen at each follow-up visit, we can choose to treat and extend for longer periods. Evaluation of the findings in those types of cases provide a solid foundation for the decision to treat or not to treat.
That is not always the case. There are instances where OCTA will show an evolution toward extensive atrophy or an evolution toward an extensive scarring process with an increase of fibrosis. We know that an active hyper-signal on OCTA corresponds to CNV, but cases such as those that evolve toward extensive atrophy, scarring, and increased fibrosis need more than injections. Comprehensive multimodal imaging provides diagnostic information and specific treatment about these inflammatory CNV cases, which are distinctly different from those of AMD at diagnosis. These CNV are more fibrous and are associated with dilated choroidal vessels. Imaging shows voluminous hyper-signal, less branching, and less vessel termini.
SS-OCT and OCTA: Game Changers
Two game-changing benefits of SS-OCT and OCTA are no dye injection and no side effects. We have to perform, however, a careful segmentation to identify the presence and the type of hyper-signal on OCTA and to recognize all artifacts, such as back-shadowing on OCT-B scans, and other artifacts to avoid potential diagnostic pitfalls.
In conclusion, I find that OCTA provides a complete description of type and activity of CNV and active versus quiescent versus scarring. Triton OCTA achieves a customized follow-up adapting rhythm of injections. SS-OCT angiography is a useful tool in clinical practice, and we are waiting for quantification of flow.
1. Coscas GJ, Lupidi M, Coscas F, et al. Optical coherence tomography angiography versus traditional multimodal imaging in assessing the activity of exudative age-related macular degeneration: a new diagnostic challenge. Retina. 2015;35(11):2219-2228.
Florence Coscas, MD
• Centre Ophtalmologique de l’Odéon, Paris VI - UPEC Creteil, Paris XII
• financial disclosures: Allergan; Bayer; Heidelberg (FA, ICG and structural OCT); Novartis; Roche; Santen; and Topcon