Guest Editorial

The OCT-A Revolution

By SriniVas R. Sadda, MD

If one uses the number of OCT angiography presentations and posters at scientific meetings, or the number of new OCT-A publications in peer-reviewed journals as benchmark metrics, OCT-A is clearly one of the hottest topics in ophthalmology. But why? Is it ready for prime time, and do all ophthalmologists need it to practice? These are key questions we should all be asking.

But first, what is OCT-A? This is a technology or approach by which OCT images are obtained and processed such that motion within the images can be detected. This is primarily achieved by repeatedly and rapidly scanning the same fundus location and comparing the signal between the B-scans to identify regions of the image which are changing over time with regards to brightness or phase or both. These changes are presumably due to motion, and, if one can exclude eye motion by tracking or image processing, much of the residual motion will be due to flow within blood vessels. What this means is that blood vessels, like those in the retina, can be seen in tremendous detail with a quick scan acquisition and without invasive dye. Also, these scans are obtainable via OCT devices often already in our clinics, are comfortable for patients to comply with and easy for our operators to obtain.

OCT-A also provides better vascular detail (e.g. the radial peripapillary capillary network is visible), is depth-resolved (we can separately study the superficial and deep retinal capillaries and choriocapillaris), and because of its high contrast, it lends itself to automatic, quantitative analysis (e.g. capillary density). With these advantages, it is not surprising that palpable excitement exists about OCT-A, and that there has been an explosion of articles that use OCT-A to study normal vascular morphology/physiology as well as abnormalities in various diseases. The proposed disease applications range from glaucoma and other optic nerve disorders to retinal vascular diseases to choroidal vascular disorders (e.g. choroidal neovascularization, inflammatory and degenerative diseases).

OCT-A holds great promise, but balance this optimism with recognition of the following important limitations. First, the technology and processing algorithms are evolving, so results today may be different tomorrow. Second, though the vascular detail is remarkable, only vascular structures that have flow within the velocity range of the OCT instrument and processing method will be seen; flow that is too fast or too slow will not be detected, so structures such as some microaneurysms, retinal angiomatous proliferative lesions and vascular polyps may not always be seen. Also, OCT-A does not provide significant information regarding velocity of flow, nor is leakage from vessels visualized. And, various artifacts including segmentation, projection and signal attenuation artifact can confound accurate interpretation. Finally, and perhaps most importantly, randomized prospective clinical trial data are not available to guide us on how to best use OCT-A information, if at all, in managing patients. So, while OCT-A has great potential, do not throw away your fluorescein angiography cameras just yet! OM

OM’S GUEST EDITOR FOR NOVEMBER:

SriniVas R. Sadda, MD, is the president and chief scientific officer of the Doheny Eye Institute, the Stephen J. Ryan – Arnold and Mabel Beckman endowed presidential chair and professor of ophthalmology at the University of California – Los Angeles (UCLA) Geffen School of Medicine. Dr. Sadda was the principal investigator on more than 30 trials, including phase III studies of ranibizumab, preservative-free triamcinolone acetonide and a dexamethasone posterior segment drug delivery system.