Imaging the retinal vasculature

Dye-based angiography techniques still holding their value

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Although fluorescein angiography (FA) and indocyanine green angiography (ICGA) have been the gold standard techniques for imaging retinal and choroidal vessels, their place as tools for diagnosis and management is being challenged subsequent to the advances occurring in optical coherence tomography (OCT) imaging. Nevertheless, despite their limitations and downsides, at least for now the dye-based techniques still have a role to play in clinical care, according to speakers who discussed this topic at WOC 2016 in Guadalajara, Mexico. Caio Regatieri MD, PhD compared and contrasted findings from imaging performed using FA and OCT angiography (OCTA) for a variety of diseases. He noted that FA is more time-consuming than OCTA and is not only invasive, but also carries risk for systemic side effects from the intravenous contrast injection. OCTA imaging is fast, non-invasive, and stands alone for providing blood flow and volumetric data. Yet, there are also situations where FA provides unique information. “I believe we still need to use FA in some cases. However, OCTA is revolutionary technology. We still have a lot to learn, and its development is continuing,” said Dr Regatieri, of Tufts University, Boston, USA, and Federal University of São Paolo, Brazil. EVALUATING ISCHEMIA In his presentation, Dr Regatieri showed how FA easily identifies retinal angiomatous proliferation lesions and choroidal serous retinopathy. In addition, he highlighted the utility of FA for diagnosing and guiding treatment decisions in eyes with diffuse or focal macular oedema. FA is also useful for evaluating ischaemia, and in a comparative study of patients with diabetes, FA and OCTA provided comparable information about the macular area of ischaemia, Dr Regatieri said. He noted that both FA and OCTA can be used to evaluate microaneurysms, although OCTA may miss these lesions if the blood flow velocity is slow. In another example, Dr Regatieri showed how the vessels of diffuse vasculitis in an eye with posterior uveitis were visible by FA staining, but difficult to identify on OCTA because of capillary dropout and the absence of blood flow. As another limitation, OCTA can currently only be used to evaluate vessels in the macula, whereas peripheral vessels can be imaged using ultra-widefield FA technology. “Now, however, we also have ultra-widefield swept-source OCT that can evaluate 100° of the retina, and it will help us with the identification of vessels in the periphery,” Dr Regatieri said. Daniela Ferrara MD, PhD reviewed the utility of ICGA, en face OCT, and OCTA in a series of cases representing the pachychoroid spectrum diseases of the macula. She acknowledged that ICGA is invasive and time-consuming. In addition, the bi-dimensional nature of the exam represents a fundamental limitation as it precludes the ability to identify certain changes and to determine their exact location in the chorioretinal tissue. However, relative to OCTA, ICGA is much less prone to blockage, motion or projection artefacts and segmentation errors. In addition, the performance of OCTA depends on the velocity of vascular blood flow, which must exceed a certain threshold in order to be documented by the current algorithms. “There are potential solutions for all of the critical limitations of OCTA, and they are currently being developed. While we are in the transition phase towards a reliable and fully non-invasive clinical assessment, however, ICGA can be especially useful in the investigation of challenging choroidal and retinal diseases, and it can definitely assist in the interpretation of en face OCT and OCTA,” said Dr Ferrara, of Tufts University, Boston, USA. Cases presented by Dr Ferrara included eyes with central serous chorioretinopathy where she showed ICGA was useful for differential diagnosis, but unlike structural en face OCT, was unable to identify individual vessels in the inner and outer choroid. BETTER TECHNOLOGIES She also showed images from eyes with polypoidal choroidal vasculopathy where ICGA proved superior to OCTA for identifying some of the polyps. In one case where there was an accumulation of lipid, blood, and dense subretinal and sub-RPE fibrinoid material, Dr Ferrara explained that the OCT signal was likely absent underneath the RPE due to image artefact. She said the issue in another polypoidal case, which featured a mature neovascular complex, was that the blood flow within the vascular network was below the velocity range captured by OCT. “ICGA was not only instrumental in documenting the polyps in these eyes, but it showed the branch vascular network and the full extension of the neovascular complex that also could not be readily appreciated with OCTA alone. These challenges with OCTA, however, may be overcome in the future with better technologies,” she concluded. Caio Regatieri: caiore@gmail.com Daniela Ferrara: daniela@ferrara.md Back to Previous
Tags: fluorescein angiography, indocanine green angiography